File:  [LON-CAPA] / loncom / interface / loncoursedata.pm
Revision 1.182: download - view: text, annotated - select for diffs
Wed May 2 01:33:48 2007 UTC (16 years, 11 months ago) by albertel
Branches: MAIN
CVS tags: version_2_5_X, version_2_5_2, version_2_5_1, version_2_5_0, version_2_4_X, version_2_4_99_0, version_2_4_2, version_2_4_1, version_2_4_0, version_2_3_99_0, HEAD
- switch Store to Save

# The LearningOnline Network with CAPA
#
# $Id: loncoursedata.pm,v 1.182 2007/05/02 01:33:48 albertel Exp $
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# /home/httpd/html/adm/gpl.txt
#
# http://www.lon-capa.org/
#
###

=pod

=head1 NAME

loncoursedata

=head1 SYNOPSIS

Set of functions that download and process student and course information.

=head1 PACKAGES USED

  Apache::lonnet
  Apache::longroup
  Time::HiRes
  Apache::lonmysql
  LONCAPA
  Digest::MD5
 
=cut

package Apache::loncoursedata;

use strict;
use Apache::lonnet;
use Apache::longroup();
use Time::HiRes();
use Apache::lonmysql();
use LONCAPA;
use Digest::MD5();

=pod

=head1 DOWNLOAD INFORMATION

This section contains all the functions that get data from other servers 
and/or itself.

=cut

################################################
################################################

=pod

=item &make_into_hash($values);

Returns a reference to a hash as described by $values.  $values is
assumed to be the result of 
    join(':',map {&escape($_)} %orighash);

This is a helper function for get_current_state.

=cut

################################################
################################################
sub make_into_hash {
    my $values = shift;
    my %tmp = map { &unescape($_); } split(':',$values);
    return \%tmp;
}


################################################
################################################

=pod

=head1 LOCAL DATA CACHING SUBROUTINES

The local caching is done using MySQL.  There is no fall-back implementation
if MySQL is not running.

The programmers interface is to call &get_current_state() or some other
primary interface subroutine (described below).  The internals of this 
storage system are documented here.

There are six tables used to store student performance data (the results of
a dumpcurrent).  Each of these tables is created in MySQL with a name of
$courseid_*****, where ***** is 'symb', 'part', or whatever is appropriate 
for the table.  The tables and their purposes are described below.

Some notes before we get started.

Each table must have a PRIMARY KEY, which is a column or set of columns which
will serve to uniquely identify a row of data.  NULL is not allowed!

INDEXes work best on integer data.

JOIN is used to combine data from many tables into one output.

lonmysql.pm is used for some of the interface, specifically the table creation
calls.  The inserts are done in bulk by directly calling the database handler.
The SELECT ... JOIN statement used to retrieve the data does not have an
interface in lonmysql.pm and I shudder at the thought of writing one.

=head3 Table Descriptions

=over 4

=item Tables used to store meta information

The following tables hold data required to keep track of the current status
of a students data in the tables or to look up the students data in the tables.

=over 4

=item $symb_table

The symb_table has two columns.  The first is a 'symb_id' and the second
is the text name for the 'symb' (limited to 64k).  The 'symb_id' is generated
automatically by MySQL so inserts should be done on this table with an
empty first element.  This table has its PRIMARY KEY on the 'symb_id'.

=item $part_table

The part_table has two columns.  The first is a 'part_id' and the second
is the text name for the 'part' (limited to 100 characters).  The 'part_id' is
generated automatically by MySQL so inserts should be done on this table with
an empty first element.  This table has its PRIMARY KEY on the 'part' (100
characters) and a KEY on 'part_id'.

=item $student_table

The student_table has 7 columns.  The first is a 'student_id' assigned by 
MySQL.  The second is 'student' which is username:domain.  The third through
fifth are 'section', 'status' (enrollment status), and 'classification' 
(to be used in the future).  The sixth and seventh ('updatetime' and 
'fullupdatetime') contain the time of last update and full update of student
data.  This table has its PRIMARY KEY on the 'student_id' column and is indexed
on 'student', 'section', and 'status'.

=item $groupnames_table

The groupnames_table has 2 columns.  The first is a 'group_id' assigned by 
MySQL.  The second is 'groupname' which is the name of the group in the course.

=item $students_groups_table

The students_groups_table has 2 columns.  The first is the 'student_id', and the 
second is the 'group_id'. These two columns comprise the PRIMARY KEY for this 
table, as an individual student may be affiliated with more than one group at
any time. This table is indexed on both student_id and group_id.

=back 

=item Tables used to store current status data

The following tables store data only about the students current status on 
a problem, meaning only the data related to the last attempt on a problem.

=over 4

=item $performance_table

The performance_table has 9 columns.  The first three are 'symb_id', 
'student_id', and 'part_id'.  These comprise the PRIMARY KEY for this table
and are directly related to the $symb_table, $student_table, and $part_table
described above.  MySQL does better indexing on numeric items than text,
so we use these three "index tables".  The remaining columns are
'solved', 'tries', 'awarded', 'award', 'awarddetail', and 'timestamp'.
These are either the MySQL type TINYTEXT or various integers ('tries' and 
'timestamp').  This table has KEYs of 'student_id' and 'symb_id'.
For use of this table, see the functions described below.

=item $parameters_table

The parameters_table holds the data that does not fit neatly into the
performance_table.  The parameters table has four columns: 'symb_id',
'student_id', 'parameter', and 'value'.  'symb_id', 'student_id', and
'parameter' comprise the PRIMARY KEY for this table.  'parameter' is 
limited to 255 characters.  'value' is limited to 64k characters.

=back

=item Tables used for storing historic data

The following tables are used to store almost all of the transactions a student
has made on a homework problem.  See loncapa/docs/homework/datastorage for 
specific information about each of the parameters stored.  

=over 4

=item $fulldump_response_table

The response table holds data (documented in loncapa/docs/homework/datastorage)
associated with a particular response id which is stored when a student 
attempts a problem.  The following are the columns of the table, in order:
'symb_id','part_id','response_id','student_id','transaction','tries',
'awarddetail', 'response_specific', 'response_specific_value',
'response_specific_2', 'response_specific_value_2', and 'submission
(the text of the students submission).  The primary key is based on the
first five columns listed above.

=item $fulldump_part_table

The part table holds data (documented in loncapa/docs/homework/datastorage)
associated with a particular part id which is stored when a student attempts
a problem.  The following are the columns of the table, in order:
'symb_id','part_id','student_id','transaction','tries','award','awarded',
and 'previous'.  The primary key is based on the first five columns listed 
above.

=item $fulldump_timestamp_table

The timestamp table holds the timestamps of the transactions which are
stored in $fulldump_response_table and $fulldump_part_table.  This data is
about both the response and part data.  Columns: 'symb_id','student_id',
'transaction', and 'timestamp'.  
The primary key is based on the first 3 columns.

=item $weight_table

The weight table holds the weight for the problems used in the class.
Whereas the weight of a problem can vary by section and student the data
here is applied to the class as a whole.
Columns: 'symb_id','part_id','response_id','weight'.

=back

=back

=head3 Important Subroutines

Here is a brief overview of the subroutines which are likely to be of 
interest:

=over 4

=item &get_current_state(): programmers interface.

=item &init_dbs(): table creation

=item &update_student_data(): data storage calls

=item &get_student_data_from_performance_cache(): data retrieval

=back

=head3 Main Documentation

=over 4

=cut

################################################
################################################

################################################
################################################
{ # Begin scope of table identifiers

my $current_course ='';
my $symb_table;
my $part_table;
my $student_table;
my $groupnames_table;
my $students_groups_table;
my $performance_table;
my $parameters_table;
my $fulldump_response_table;
my $fulldump_part_table;
my $fulldump_timestamp_table;
my $weight_table;

my @Tables;
################################################
################################################

=pod

=item &init_dbs()

Input: course id

Output: 0 on success, positive integer on error

This routine issues the calls to lonmysql to create the tables used to
store student data.

=cut

################################################
################################################
sub init_dbs {
    my ($courseid,$drop) = @_;
    &setup_table_names($courseid);
    #
    # Drop any of the existing tables
    if ($drop) {
        foreach my $table (@Tables) {
            &Apache::lonmysql::drop_table($table);
        }
    }
    #
    # Note - changes to this table must be reflected in the code that 
    # stores the data (calls &Apache::lonmysql::store_row with this table
    # id
    my $symb_table_def = {
        id => $symb_table,
        permanent => 'no',
        columns => [{ name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL',
                      auto_inc     => 'yes', },
                    { name => 'symb',
                      type => 'MEDIUMTEXT',
                      restrictions => 'NOT NULL'},
                    ],
        'PRIMARY KEY' => ['symb_id'],
    };
    #
    my $part_table_def = {
        id => $part_table,
        permanent => 'no',
        columns => [{ name => 'part_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL',
                      auto_inc     => 'yes', },
                    { name => 'part',
                      type => 'VARCHAR(100) BINARY',
                      restrictions => 'NOT NULL'},
                    ],
        'PRIMARY KEY' => ['part (100)'],
        'KEY' => [{ columns => ['part_id']},],
    };
    #
    my $student_table_def = {
        id => $student_table,
        permanent => 'no',
        columns => [{ name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL',
                      auto_inc     => 'yes', },
                    { name => 'student',
                      type => 'VARCHAR(100) BINARY',
                      restrictions => 'NOT NULL UNIQUE'},
                    { name => 'section',
                      type => 'VARCHAR(100) BINARY',
                      restrictions => 'NOT NULL'},
                    { name => 'start',
                      type => 'INT',
                      restrictions => 'NOT NULL'},
                    { name => 'end',
                      type => 'INT',
                      restrictions => 'NOT NULL'},
                    { name => 'classification',
                      type => 'VARCHAR(100) BINARY', },
                    { name => 'updatetime',
                      type => 'INT UNSIGNED'},
                    { name => 'fullupdatetime',
                      type => 'INT UNSIGNED'},
                    ],
        'PRIMARY KEY' => ['student_id'],
        'KEY' => [{ columns => ['student (100)',
                                'section (100)',
                                'start',
				'end']},],
    };
    #
    my $groupnames_table_def = {
        id => $groupnames_table,
        permanent => 'no',
        columns => [{ name => 'group_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL',
                      auto_inc => 'yes', },
                    { name => 'groupname',
                      type => 'VARCHAR(100) BINARY',
                      restrictions => 'NOT NULL UNIQUE'},
                   ],
        'PRIMARY KEY' => ['group_id'],
        'KEY' => [{ columns => ['groupname (100)',]},],
    };
    #
    my $students_groups_table_def = {
        id => $students_groups_table,
        permanent => 'no',
        columns => [{ name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL', },
                    { name => 'group_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL', },
                   ],
        'PRIMARY KEY' => ['student_id','group_id'],
        'KEY' => [{ columns => ['student_id'] },
                  { columns => ['group_id'] },],
    };
    #
    my $performance_table_def = {
        id => $performance_table,
        permanent => 'no',
        columns => [{ name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'part_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'part',
                      type => 'VARCHAR(100) BINARY',
                      restrictions => 'NOT NULL'},                    
                    { name => 'solved',
                      type => 'TINYTEXT' },
                    { name => 'tries',
                      type => 'SMALLINT UNSIGNED' },
                    { name => 'awarded',
                      type => 'REAL' },
                    { name => 'award',
                      type => 'TINYTEXT' },
                    { name => 'awarddetail',
                      type => 'TINYTEXT' },
                    { name => 'timestamp',
                      type => 'INT UNSIGNED'},
                    ],
        'PRIMARY KEY' => ['symb_id','student_id','part_id'],
        'KEY' => [{ columns=>['student_id'] },
                  { columns=>['symb_id'] },],
    };
    #
    my $fulldump_part_table_def = {
        id => $fulldump_part_table,
        permanent => 'no',
        columns => [
                    { name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'part_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'transaction',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'tries',
                      type => 'SMALLINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'award',
                      type => 'TINYTEXT' },
                    { name => 'awarded',
                      type => 'REAL' },
                    { name => 'previous',
                      type => 'SMALLINT UNSIGNED' },
#                    { name => 'regrader',
#                      type => 'TINYTEXT' },
#                    { name => 'afterduedate',
#                      type => 'TINYTEXT' },
                    ],
        'PRIMARY KEY' => ['symb_id','part_id','student_id','transaction'],
        'KEY' => [
                  { columns=>['symb_id'] },
                  { columns=>['part_id'] },
                  { columns=>['student_id'] },
                  ],
    };
    #
    my $fulldump_response_table_def = {
        id => $fulldump_response_table,
        permanent => 'no',
        columns => [
                    { name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'part_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'response_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'transaction',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'awarddetail',
                      type => 'TINYTEXT' },
#                    { name => 'message',
#                      type => 'CHAR BINARY'},
                    { name => 'response_specific',
                      type => 'TINYTEXT' },
                    { name => 'response_specific_value',
                      type => 'TINYTEXT' },
                    { name => 'response_specific_2',
                      type => 'TINYTEXT' },
                    { name => 'response_specific_value_2',
                      type => 'TINYTEXT' },
                    { name => 'submission',
                      type => 'TEXT'},
                    ],
            'PRIMARY KEY' => ['symb_id','part_id','response_id','student_id',
                              'transaction'],
            'KEY' => [
                      { columns=>['symb_id'] },
                      { columns=>['part_id','response_id'] },
                      { columns=>['student_id'] },
                      ],
    };
    my $fulldump_timestamp_table_def = {
        id => $fulldump_timestamp_table,
        permanent => 'no',
        columns => [
                    { name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'transaction',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL' },
                    { name => 'timestamp',
                      type => 'INT UNSIGNED'},
                    ],
        'PRIMARY KEY' => ['symb_id','student_id','transaction'],
        'KEY' => [
                  { columns=>['symb_id'] },
                  { columns=>['student_id'] },
                  { columns=>['transaction'] },
                  ],
    };
    #
    my $parameters_table_def = {
        id => $parameters_table,
        permanent => 'no',
        columns => [{ name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'student_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'parameter',
                      type => 'TINYTEXT',
                      restrictions => 'NOT NULL'  },
                    { name => 'value',
                      type => 'MEDIUMTEXT' },
                    ],
        'PRIMARY KEY' => ['symb_id','student_id','parameter (255)'],
    };
    #
    my $weight_table_def = {
        id => $weight_table,
        permanent => 'no',
        columns => [{ name => 'symb_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'part_id',
                      type => 'MEDIUMINT UNSIGNED',
                      restrictions => 'NOT NULL'  },
                    { name => 'weight',
                      type => 'REAL',
                      restrictions => 'NOT NULL'  },
                    ],
        'PRIMARY KEY' => ['symb_id','part_id'],
    };
    #
    # Create the tables
    my $tableid;
    $tableid = &Apache::lonmysql::create_table($symb_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating symb_table: ".
                                 &Apache::lonmysql::get_error());
        return 1;
    }
    #
    $tableid = &Apache::lonmysql::create_table($part_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating part_table: ".
                                 &Apache::lonmysql::get_error());
        return 2;
    }
    #
    $tableid = &Apache::lonmysql::create_table($student_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating student_table: ".
                                 &Apache::lonmysql::get_error());
        return 3;
    }
    #
    $tableid = &Apache::lonmysql::create_table($performance_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating preformance_table: ".
                                 &Apache::lonmysql::get_error());
        return 5;
    }
    #
    $tableid = &Apache::lonmysql::create_table($parameters_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating parameters_table: ".
                                 &Apache::lonmysql::get_error());
        return 6;
    }
    #
    $tableid = &Apache::lonmysql::create_table($fulldump_part_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating fulldump_part_table: ".
                                 &Apache::lonmysql::get_error());
        return 7;
    }
    #
    $tableid = &Apache::lonmysql::create_table($fulldump_response_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating fulldump_response_table: ".
                                 &Apache::lonmysql::get_error());
        return 8;
    }
    $tableid = &Apache::lonmysql::create_table($fulldump_timestamp_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating fulldump_timestamp_table: ".
                                 &Apache::lonmysql::get_error());
        return 9;
    }
    $tableid = &Apache::lonmysql::create_table($weight_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating weight_table: ".
                                 &Apache::lonmysql::get_error());
        return 10;
    }
    $tableid = &Apache::lonmysql::create_table($groupnames_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating groupnames_table: ".
                                 &Apache::lonmysql::get_error());
        return 11;
    }
    $tableid = &Apache::lonmysql::create_table($students_groups_table_def);
    if (! defined($tableid)) {
        &Apache::lonnet::logthis("error creating student_groups_table: ".
                                 &Apache::lonmysql::get_error());
        return 12;
    }
    return 0;
}

################################################
################################################

=pod

=item &delete_caches()

This routine drops all the tables associated with a course from the 
MySQL database.

Input: course id (optional, determined by environment if omitted) 

Returns: nothing

=cut

################################################
################################################
sub delete_caches {
    my $courseid = shift;
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    #
    &setup_table_names($courseid);
    #
    my $dbh = &Apache::lonmysql::get_dbh();
    foreach my $table (@Tables) {
        my $command = 'DROP TABLE '.$table.';';
        $dbh->do($command);
        if ($dbh->err) {
            &Apache::lonnet::logthis($command.' resulted in error: '.$dbh->errstr);
        }
    }
    return;
}

################################################
################################################

=pod

=item &get_part_id()

Get the MySQL id of a problem part string.

Input: $part

Output: undef on error, integer $part_id on success.

=item &get_part()

Get the string describing a part from the MySQL id of the problem part.

Input: $part_id

Output: undef on error, $part string on success.

=cut

################################################
################################################

my $have_read_part_table = 0;
my %ids_by_part;
my %parts_by_id;

sub get_part_id {
    my ($part) = @_;
    $part = 0 if (! defined($part));
    if (! $have_read_part_table) {
        my @Result = &Apache::lonmysql::get_rows($part_table);
        foreach (@Result) {
            $ids_by_part{$_->[1]}=$_->[0];
        }
        $have_read_part_table = 1;
    }
    if (! exists($ids_by_part{$part})) {
        &Apache::lonmysql::store_row($part_table,[undef,$part]);
        undef(%ids_by_part);
        my @Result = &Apache::lonmysql::get_rows($part_table);
        foreach (@Result) {
            $ids_by_part{$_->[1]}=$_->[0];
        }
    }
    return $ids_by_part{$part} if (exists($ids_by_part{$part}));
    return undef; # error
}

sub get_part {
    my ($part_id) = @_;
    if (! exists($parts_by_id{$part_id})  || 
        ! defined($parts_by_id{$part_id}) ||
        $parts_by_id{$part_id} eq '') {
        my @Result = &Apache::lonmysql::get_rows($part_table);
        foreach (@Result) {
            $parts_by_id{$_->[0]}=$_->[1];
        }
    }
    return $parts_by_id{$part_id} if(exists($parts_by_id{$part_id}));
    return undef; # error
}

################################################
################################################

=pod

=item &get_symb_id()

Get the MySQL id of a symb.

Input: $symb

Output: undef on error, integer $symb_id on success.

=item &get_symb()

Get the symb associated with a MySQL symb_id.

Input: $symb_id

Output: undef on error, $symb on success.

=cut

################################################
################################################

my $have_read_symb_table = 0;
my %ids_by_symb;
my %symbs_by_id;

sub get_symb_id {
    my ($symb) = @_;
    if (! $have_read_symb_table) {
        my @Result = &Apache::lonmysql::get_rows($symb_table);
        foreach (@Result) {
            $ids_by_symb{$_->[1]}=$_->[0];
        }
        $have_read_symb_table = 1;
    }
    if (! exists($ids_by_symb{$symb})) {
        &Apache::lonmysql::store_row($symb_table,[undef,$symb]);
        undef(%ids_by_symb);
        my @Result = &Apache::lonmysql::get_rows($symb_table);
        foreach (@Result) {
            $ids_by_symb{$_->[1]}=$_->[0];
        }
    }
    return $ids_by_symb{$symb} if(exists( $ids_by_symb{$symb}));
    return undef; # error
}

sub get_symb {
    my ($symb_id) = @_;
    if (! exists($symbs_by_id{$symb_id})  || 
        ! defined($symbs_by_id{$symb_id}) ||
        $symbs_by_id{$symb_id} eq '') {
        my @Result = &Apache::lonmysql::get_rows($symb_table);
        foreach (@Result) {
            $symbs_by_id{$_->[0]}=$_->[1];
        }
    }
    return $symbs_by_id{$symb_id} if(exists( $symbs_by_id{$symb_id}));
    return undef; # error
}

################################################
################################################

=pod

=item &get_student_id()

Get the MySQL id of a student.

Input: $sname, $dom

Output: undef on error, integer $student_id on success.

=item &get_student()

Get student username:domain associated with the MySQL student_id.

Input: $student_id

Output: undef on error, string $student (username:domain) on success.

=cut

################################################
################################################

my $have_read_student_table = 0;
my %ids_by_student;
my %students_by_id;

sub get_student_id {
    my ($sname,$sdom) = @_;
    my $student = $sname.':'.$sdom;
    if (! $have_read_student_table) {
        my @Result = &Apache::lonmysql::get_rows($student_table);
        foreach (@Result) {
            $ids_by_student{$_->[1]}=$_->[0];
        }
        $have_read_student_table = 1;
    }
    if (! exists($ids_by_student{$student})) {
        &populate_student_table();
        undef(%ids_by_student);
        undef(%students_by_id);
        my @Result = &Apache::lonmysql::get_rows($student_table);
        foreach (@Result) {
            $ids_by_student{$_->[1]}=$_->[0];
        }
    }
    return $ids_by_student{$student} if(exists( $ids_by_student{$student}));
    return undef; # error
}

sub get_student {
    my ($student_id) = @_;
    if (! exists($students_by_id{$student_id})  || 
        ! defined($students_by_id{$student_id}) ||
        $students_by_id{$student_id} eq '') {
        my @Result = &Apache::lonmysql::get_rows($student_table);
        foreach (@Result) {
            $students_by_id{$_->[0]}=$_->[1];
        }
    }
    return $students_by_id{$student_id} if(exists($students_by_id{$student_id}));
    return undef; # error
}

sub populate_student_table {
    my ($courseid) = @_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    &setup_table_names($courseid);
    &init_dbs($courseid,0);
    my $dbh = &Apache::lonmysql::get_dbh();
    my $request = 'INSERT IGNORE INTO '.$student_table.
        "(student,section,start,end) VALUES ";
    my $cdom = $env{'course.'.$courseid.'.domain'};
    my $cnum = $env{'course.'.$courseid.'.num'};
    my $classlist = &get_classlist($cdom,$cnum);
    my $student_count=0;
    while (my ($student,$data) = each %$classlist) {
        my ($section,$start,$end) = ($data->[&CL_SECTION()],
				     $data->[&CL_START()],
				     $data->[&CL_END()]);
        if ($section eq '' || $section =~ /^\s*$/) {
            $section = 'none';
        }
	if (!defined($start)) { $start = 0; }
	if (!defined($end))   { $end   = 0; }
        $request .= "('".$student."','".$section."','".$start."','".$end."'),";
        $student_count++;
    }
    return if ($student_count == 0);
    chop($request);
    $dbh->do($request);
    if ($dbh->err()) {
        &Apache::lonnet::logthis("error ".$dbh->errstr().
                                 " occured executing \n".
                                 $request);
    }
    return;
}

my $have_read_groupnames_table = 0;
my %ids_by_groupname;

sub get_group_id {
    my ($groupname) = @_;
    if (! $have_read_groupnames_table) {
        my @Result = &Apache::lonmysql::get_rows($groupnames_table);
        foreach (@Result) {
            $ids_by_groupname{$_->[1]}=$_->[0];
        }
        $have_read_groupnames_table = 1;
    }
    if (! exists($ids_by_groupname{$groupname})) {
        &populate_groupnames_table();
        undef(%ids_by_groupname);
        my @Result = &Apache::lonmysql::get_rows($groupnames_table);
        foreach (@Result) {
            $ids_by_groupname{$_->[1]}=$_->[0];
        }
    }
    if (exists($ids_by_groupname{$groupname})) {
        return $ids_by_groupname{$groupname};
    }
    return undef; # error
}

sub populate_groupnames_table {
    my ($courseid) = @_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    &setup_table_names($courseid);
    &init_dbs($courseid,0);
    my $dbh = &Apache::lonmysql::get_dbh();
    my $cdom = $env{'course.'.$courseid.'.domain'};
    my $cnum = $env{'course.'.$courseid.'.num'};
    my %curr_groups = &Apache::longroup::coursegroups($cdom,$cnum);
    return if (!%curr_groups);
    my $request = 'INSERT IGNORE INTO '.$groupnames_table.
                  '(groupname) VALUES ';
    foreach my $groupname (sort(keys(%curr_groups)),'none') {
        $request .= "('".$groupname."'),";
    }
    chop($request);
    $dbh->do($request);
    if ($dbh->err()) {
        &Apache::lonnet::logthis("error ".$dbh->errstr().
                                 " occured executing \n".
                                 $request);
    }
    return;
}

my $have_read_studentsgroups_table = 0;
my %groupids_by_studentid;

sub get_students_groupids {
    my ($student_id) = @_;
    if (! $have_read_studentsgroups_table) {
        my @Result = &Apache::lonmysql::get_rows($students_groups_table);
        foreach (@Result) {
            push(@{$groupids_by_studentid{$_->[0]}},$_->[1]);
        }
        $have_read_studentsgroups_table = 1;
    }
    if (! exists($groupids_by_studentid{$student_id})) {
        &populate_students_groups_table();
        undef(%groupids_by_studentid);
        my @Result = &Apache::lonmysql::get_rows($students_groups_table);
        foreach (@Result) {
            push(@{$groupids_by_studentid{$_->[0]}},$_->[1]);
        }
    }
    if (exists($groupids_by_studentid{$student_id})) {
        if (ref($groupids_by_studentid{$student_id}) eq 'ARRAY') {
            return @{$groupids_by_studentid{$student_id}};
        }
    }
    return undef; # error
}


sub populate_students_groups_table {
    my ($courseid) = @_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    &setup_table_names($courseid);
    &init_dbs($courseid,0);
    my $dbh = &Apache::lonmysql::get_dbh();
    my $request = 'INSERT IGNORE INTO '.$students_groups_table.
        "(student_id,group_id) VALUES ";
    my $cdom = $env{'course.'.$courseid.'.domain'};
    my $cnum = $env{'course.'.$courseid.'.num'};
    my ($classlist,$keylist) = &get_classlist($cdom,$cnum);
    my ($classgroups,$studentgroups) = &get_group_memberships($classlist,
                                                              $keylist,
                                                              $cdom,$cnum);
    my $record_count = 0;
    foreach my $student (sort(keys(%{$classgroups}))) {
        my $student_id = &get_student_id(split(':',$student));
        my @studentsgroups = &get_students_groups($student,'Active',$classgroups);
        if (@studentsgroups < 1) {
            @studentsgroups = ('none');
        }
        foreach my $groupname (@studentsgroups) {
            my $group_id = &get_group_id($groupname);
            $request .= "('".$student_id."','".$group_id."'),";
            $record_count++;
        }
    }
    return if ($record_count == 0);
    chop($request);
    $dbh->do($request);
    if ($dbh->err()) {
        &Apache::lonnet::logthis("error ".$dbh->errstr().
                                 " occured executing \n".
                                 $request);
    }
    return;
}

################################################
################################################

=pod

=item &clear_internal_caches()

Causes the internal caches used in get_student_id, get_student,
get_symb_id, get_symb, get_part_id, and get_part to be undef'd.

Needs to be called before the first operation with the MySQL database
for a given Apache request.

=cut

################################################
################################################
sub clear_internal_caches {
    $have_read_part_table = 0;
    undef(%ids_by_part);
    undef(%parts_by_id);
    $have_read_symb_table = 0;
    undef(%ids_by_symb);
    undef(%symbs_by_id);
    $have_read_student_table = 0;
    undef(%ids_by_student);
    undef(%students_by_id);
    $have_read_groupnames_table = 0;
    undef(%ids_by_groupname);
}


################################################
################################################

sub symb_is_for_task {
    my ($symb) = @_;
    return ($symb =~ /\.task$/);
}

################################################
################################################

=pod

=item &update_full_student_data($sname,$sdom,$courseid)

Does a lonnet::dump on a student to populate the courses tables.

Input: $sname, $sdom, $courseid

Output: $returnstatus

$returnstatus is a string describing any errors that occured.  'okay' is the
default.

This subroutine loads a students data using lonnet::dump and inserts
it into the MySQL database.  The inserts are done on three tables, 
$fulldump_response_table, $fulldump_part_table, and $fulldump_timestamp_table.
The INSERT calls are made directly by this subroutine, not through lonmysql 
because we do a 'bulk'insert which takes advantage of MySQLs non-SQL 
compliant INSERT command to insert multiple rows at a time.  
If anything has gone wrong during this process, $returnstatus is updated with 
a description of the error.

Once the "fulldump" tables are updated, the tables used for chart and
spreadsheet (which hold only the current state of the student on their
homework, not historical data) are updated.  If all updates have occured 
successfully, $student_table is updated to reflect the time of the update.

Notice we do not insert the data and immediately query it.  This means it
is possible for there to be data returned this first time that is not 
available the second time.  CYA.

=cut

################################################
################################################
sub update_full_student_data {
    my ($sname,$sdom,$courseid) = @_;
    #
    # Set up database names
    &setup_table_names($courseid);
    #
    my $student_id = &get_student_id($sname,$sdom);
    my $student = $sname.':'.$sdom;
    #
    my $returnstatus = 'okay';
    #
    # Download students data
    my $time_of_retrieval = time;
    my @tmp = &Apache::lonnet::dumpstore($courseid,$sdom,$sname);
    if (@tmp && $tmp[0] =~ /^error/) {
        $returnstatus = 'error retrieving full student data';
        return $returnstatus;
    } elsif (! @tmp) {
        $returnstatus = 'okay: no student data';
        return $returnstatus;
    }
    my %studentdata = @tmp;
    #
    # Get database handle and clean out the tables 
    my $dbh = &Apache::lonmysql::get_dbh();
    $dbh->do('DELETE FROM '.$fulldump_response_table.' WHERE student_id='.
             $student_id);
    $dbh->do('DELETE FROM '.$fulldump_part_table.' WHERE student_id='.
             $student_id);
    $dbh->do('DELETE FROM '.$fulldump_timestamp_table.' WHERE student_id='.
             $student_id);
    #
    # Parse and store the data into a form we can handle
    my $partdata;
    my $respdata;
    while (my ($key,$value) = each(%studentdata)) {
        next if ($key =~ /^(\d+):(resource$|subnum$|keys:)/);
        my ($transaction,$symb,$parameter) = split(':',$key);
	$symb = &unescape($symb);
	$parameter = &unescape($parameter);
        my $symb_id = &get_symb_id($symb);
        if ($parameter eq 'timestamp') {
            # We can deal with 'timestamp' right away
            my @timestamp_storage = ($symb_id,$student_id,
                                     $transaction,$value);
            my $store_command = 'INSERT IGNORE INTO '.$fulldump_timestamp_table.
                " VALUES ('".join("','",@timestamp_storage)."');";
            $dbh->do($store_command);
            if ($dbh->err()) {
                &Apache::lonnet::logthis('unable to execute '.$store_command);
                &Apache::lonnet::logthis($dbh->errstr());
            }
            next;
        } elsif ($parameter eq 'version') {
            next;
	} elsif (&symb_is_for_task($symb)) {
	    next if ($parameter !~ /^resource\.(.*)\.(award|
						      awarded|
						      solved|
						      submission|
						      portfiles|
						      status|
						      version|
						      regrader)\s*$/x);
	    my ($version_and_part_id, $field) = ($1,$2);

	    next if ($version_and_part_id !~ /\./ 
		     && $field ne 'regrader' && $field ne 'version');

	    my ($version, $part, $instance) = 
		split(/\./,$version_and_part_id);

	    #skip and instance dimension or criteria specific data
	    next if (defined($instance) 
		     && $instance ne $field
		     && $instance ne 'bridgetask');
	    
	    if (!defined($part)) {
		$part = $version;
	    }
	    my $resp_id = &get_part_id('0');
	    my $part_id = &get_part_id($part);
	    
	    if ($field eq 'version') {
		# for tasks each version is an attempt at it thus
		#     version -> tries
		$partdata->{$symb_id}{$part_id}{$transaction}{'tries'}=
		    $value;
		# at new version time the record gets reset thus adding a
		# virtual response awarddetail of 'new_version'
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'response_specific'}='status';
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'response_specific_value'}='new_version';

	    } elsif ($field eq 'award' || $field eq 'awarded' 
		     || $field eq 'solved') {
		$partdata->{$symb_id}{$part_id}{$transaction}{$field}=
		    $value;
	    } elsif ($field eq 'portfiles') {
		# tasks only accepts portfolio submissions
		$value = $dbh->quote($value);
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'submission'}=$value;
	    } elsif ($field eq 'status') {
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'response_specific'}=$field;
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'response_specific_value'}=$value;
	    } elsif ($field eq 'regrader') {
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'response_specific_2'}=$field;
		$respdata->{$symb_id}{$part_id}{$resp_id}{$transaction}{'response_specific_value_2'}=$value;
	    }
	} elsif ($parameter =~ /^resource\.(.*)\.(tries|
                                                  award|
                                                  awarded|
                                                  previous|
                                                  solved|
                                                  awarddetail|
                                                  submission|
                                                  submissiongrading|
                                                  molecule)\s*$/x){
            # we do not have enough information to store an 
            # entire row, so we save it up until later.
            my ($part_and_resp_id,$field) = ($1,$2);
            my ($part,$part_id,$resp,$resp_id);
            if ($part_and_resp_id =~ /\./) {
                ($part,$resp) = split(/\./,$part_and_resp_id);
                $part_id = &get_part_id($part);
                $resp_id = &get_part_id($resp);
            } else {
                $part_id = &get_part_id($part_and_resp_id);
            }
            # Deal with part specific data
            if ($field =~ /^(tries|award|awarded|previous)$/) {
                $partdata->{$symb_id}->{$part_id}->{$transaction}->{$field}=$value;
            }
            # deal with response specific data
            if (defined($resp_id) &&
                $field =~ /^(awarddetail|
                             submission|
                             submissiongrading|
                             molecule)$/x) {
                if ($field eq 'submission') {
                    # We have to be careful with user supplied input.
                    # most of the time we are okay because it is escaped.
                    # However, there is one wrinkle: submissions which end in
                    # and odd number of '\' cause insert errors to occur.  
                    # Best trap this somehow...
                    $value = $dbh->quote($value);
                }
                if ($field eq 'submissiongrading' || 
                    $field eq 'molecule') {
                    $respdata->{$symb_id}->{$part_id}->{$resp_id}->{$transaction}->{'response_specific'}=$field;
                    $respdata->{$symb_id}->{$part_id}->{$resp_id}->{$transaction}->{'response_specific_value'}=$value;
                } else {
                    $respdata->{$symb_id}->{$part_id}->{$resp_id}->{$transaction}->{$field}=$value;
                }
            }
        }
    }
    ##
    ## Store the part data
    my $store_command = 'INSERT IGNORE INTO '.$fulldump_part_table.
        ' VALUES '."\n";
    my $store_rows = 0;
    while (my ($symb_id,$hash1) = each (%$partdata)) {
        while (my ($part_id,$hash2) = each (%$hash1)) {
            while (my ($transaction,$data) = each (%$hash2)) {
                $store_command .= "('".join("','",$symb_id,$part_id,
                                            $student_id,
                                            $transaction,
                                            $data->{'tries'},
                                            $data->{'award'},
                                            $data->{'awarded'},
                                            $data->{'previous'})."'),";
                $store_rows++;
            }
        }
    }
    if ($store_rows) {
        chop($store_command);
        $dbh->do($store_command);
        if ($dbh->err) {
            $returnstatus = 'error saving part data';
            &Apache::lonnet::logthis('insert error '.$dbh->errstr());
            &Apache::lonnet::logthis("While attempting\n".$store_command);
        }
    }
    ##
    ## Store the response data
    $store_command = 'INSERT IGNORE INTO '.$fulldump_response_table.
        ' VALUES '."\n";
    $store_rows = 0;
    while (my ($symb_id,$hash1) = each (%$respdata)) {
        while (my ($part_id,$hash2) = each (%$hash1)) {
            while (my ($resp_id,$hash3) = each (%$hash2)) {
                while (my ($transaction,$data) = each (%$hash3)) {
                    my $submission = $data->{'submission'};
                    # We have to be careful with user supplied input.
                    # most of the time we are okay because it is escaped.
                    # However, there is one wrinkle: submissions which end in
                    # and odd number of '\' cause insert errors to occur.  
                    # Best trap this somehow...
                    $submission = $dbh->quote($submission);
                    $store_command .= "('".
                        join("','",$symb_id,$part_id,
                             $resp_id,$student_id,
                             $transaction,
                             $data->{'awarddetail'},
                             $data->{'response_specific'},
                             $data->{'response_specific_value'},
                             $data->{'response_specific_2'},
                             $data->{'response_specific_value_2'}).
                             "',".$submission."),";
                    $store_rows++;
                }
            }
        }
    }
    if ($store_rows) {
        chop($store_command);
        $dbh->do($store_command);
        if ($dbh->err) {
            $returnstatus = 'error saving response data';
            &Apache::lonnet::logthis('insert error '.$dbh->errstr());
            &Apache::lonnet::logthis("While attempting\n".$store_command);
        }
    }
    ##
    ## Update the students "current" data in the performance 
    ## and parameters tables.
    my ($status,undef) = &store_student_data
        ($sname,$sdom,$courseid,
         &Apache::lonnet::convert_dump_to_currentdump(\%studentdata));
    if ($returnstatus eq 'okay' && $status ne 'okay') {
        $returnstatus = 'error saving current data:'.$status;
    } elsif ($status ne 'okay') {
        $returnstatus .= ' error saving current data:'.$status;
    }        
    ##
    ## Update the students time......
    if ($returnstatus eq 'okay') {
        &store_updatetime($student_id,$time_of_retrieval,$time_of_retrieval);
        if ($dbh->err) {
            if ($returnstatus eq 'okay') {
                $returnstatus = 'error updating student time';
            } else {
                $returnstatus = 'error updating student time';
            }
        }
    }
    return $returnstatus;
}

################################################
################################################

=pod

=item &update_student_data()

Input: $sname, $sdom, $courseid

Output: $returnstatus, \%student_data

$returnstatus is a string describing any errors that occured.  'okay' is the
default.
\%student_data is the data returned by a call to lonnet::currentdump.

This subroutine loads a students data using lonnet::currentdump and inserts
it into the MySQL database.  The inserts are done on two tables, 
$performance_table and $parameters_table.  $parameters_table holds the data 
that is not included in $performance_table.  See the description of 
$performance_table elsewhere in this file.  The INSERT calls are made
directly by this subroutine, not through lonmysql because we do a 'bulk'
insert which takes advantage of MySQLs non-SQL compliant INSERT command to 
insert multiple rows at a time.  If anything has gone wrong during this
process, $returnstatus is updated with a description of the error and
\%student_data is returned.  

Notice we do not insert the data and immediately query it.  This means it
is possible for there to be data returned this first time that is not 
available the second time.  CYA.

=cut

################################################
################################################
sub update_student_data {
    my ($sname,$sdom,$courseid) = @_;
    #
    # Set up database names
    &setup_table_names($courseid);
    #
    my $student_id = &get_student_id($sname,$sdom);
    my $student = $sname.':'.$sdom;
    #
    my $returnstatus = 'okay';
    #
    # Download students data
    my $time_of_retrieval = time;
    my %student_data = &Apache::lonnet::currentdump($courseid,$sdom,$sname);
    if (&Apache::lonnet::error(%student_data)) {
        &Apache::lonnet::logthis('error getting data for '.
                                 $sname.':'.$sdom.' in course '.$courseid.
                                 ':'.(%student_data)[0]);
        $returnstatus =(%student_data)[0] ;
        return ($returnstatus,undef);
    }
    if (scalar(keys(%student_data)) < 1) {
        return ('no data',undef);
    }
    my @Results = &store_student_data($sname,$sdom,$courseid,\%student_data);
    #
    # Set the students update time
    if ($Results[0] eq 'okay') {
        &store_updatetime($student_id,$time_of_retrieval);
    }
    #
    return @Results;
}

sub store_updatetime {
    my ($student_id,$updatetime,$fullupdatetime)=@_;
    my $values = '';
    if (defined($updatetime)) {
        $values = 'updatetime='.$updatetime.' ';
    }
    if (defined($fullupdatetime)) {
        if ($values ne '') {
            $values .= ',';
        }
        $values .= 'fullupdatetime='.$fullupdatetime.' ';
    }
    return if ($values eq '');
    my $dbh = &Apache::lonmysql::get_dbh();
    my $request = 'UPDATE '.$student_table.' SET '.$values.
        ' WHERE student_id='.$student_id.' LIMIT 1';
    $dbh->do($request);
}

sub store_student_data {
    my ($sname,$sdom,$courseid,$student_data) = @_;
    #
    my $student_id = &get_student_id($sname,$sdom);
    my $student = $sname.':'.$sdom;
    #
    my $returnstatus = 'okay';
    #
    # Remove all of the students data from the table
    my $dbh = &Apache::lonmysql::get_dbh();
    $dbh->do('DELETE FROM '.$performance_table.' WHERE student_id='.
             $student_id);
    $dbh->do('DELETE FROM '.$parameters_table.' WHERE student_id='.
             $student_id);
    #
    # Store away the data
    #
    my $starttime = Time::HiRes::time;
    my $elapsed = 0;
    my $rows_stored;
    my $store_parameters_command  = 'INSERT IGNORE INTO '.$parameters_table.
        ' VALUES '."\n";
    my $num_parameters = 0;
    my $store_performance_command = 'INSERT IGNORE INTO '.$performance_table.
        ' VALUES '."\n";
    return ('error',undef) if (! defined($dbh));
    while (my ($current_symb,$param_hash) = each(%{$student_data})) {
        #
        # make sure the symb is set up properly
        my $symb_id = &get_symb_id($current_symb);
        #
        # Parameters
        while (my ($parameter,$value) = each(%$param_hash)) {
            if ($parameter !~ /(timestamp|resource\.(.*)\.(solved|tries|awarded|award|awarddetail|previous))/) {
                my $sql_parameter = "('".join("','",
                                              $symb_id,$student_id,
                                              $parameter)."',".
                                                  $dbh->quote($value)."),\n";
                $num_parameters ++;
                if ($sql_parameter !~ /''/) {
                    $store_parameters_command .= $sql_parameter;
                    #$rows_stored++;
                }
            }
        }
        # Performance
        my %stored;
        while (my ($parameter,$value) = each(%$param_hash)) {
            next if ($parameter !~ /^resource\.(.*)\.(solved|awarded)$/);
            my $part  = $1;
	    my $which = $2;
	    next if ($part =~ /\./);
            next if (exists($stored{$part}));
            $stored{$part}++;
            #
            my $part_id = &get_part_id($part);
            next if (!defined($part_id));
	    
            my ($solved,$awarded);
	    if ($which eq 'solved') {
		$solved  = $value;
		$awarded = $param_hash->{'resource.'.$part.'.awarded'};
	    } else {
		$solved  = $param_hash->{'resource.'.$part.'.solved'};
		$awarded = $value;
	    }
            my $award   = $param_hash->{'resource.'.$part.'.award'};
            my $awarddetail = $param_hash->{'resource.'.$part.'.awarddetail'};
            my $timestamp = $param_hash->{'timestamp'};
	    my $tries   = $param_hash->{'resource.'.$part.'.tries'};
	    if (&symb_is_for_task($current_symb)) {
		$tries   = $param_hash->{'resource.'.$part.'.version'};
	    }
            #
            $solved      = '' if (! defined($solved));
            $tries       = '' if (! defined($tries));
            $awarded     = '' if (! defined($awarded));
            $award       = '' if (! defined($award));
            $awarddetail = '' if (! defined($awarddetail));
            my $sql_performance = 
                "('".join("','",$symb_id,$student_id,$part_id,$part,
                                $solved,$tries,$awarded,$award,
                                $awarddetail,$timestamp)."'),\n";
            $store_performance_command .= $sql_performance;
            $rows_stored++;
        }
    }
    if (! $rows_stored) { return ($returnstatus, undef); }
    $store_parameters_command =~ s|,\n$||;
    $store_performance_command =~ s|,\n$||;
    my $start = Time::HiRes::time;
    $dbh->do($store_performance_command);
    if ($dbh->err()) {
        &Apache::lonnet::logthis('performance bigass insert error:'.
                                 $dbh->errstr());
        &Apache::lonnet::logthis('command = '.$/.$store_performance_command);
        $returnstatus = 'error: unable to insert performance into database';
        return ($returnstatus,$student_data);
    }
    $dbh->do($store_parameters_command) if ($num_parameters>0);
    if ($dbh->err()) {
        &Apache::lonnet::logthis('parameters bigass insert error:'.
                                 $dbh->errstr());
        &Apache::lonnet::logthis('command = '.$/.$store_parameters_command);
        &Apache::lonnet::logthis('rows_stored = '.$rows_stored);
        &Apache::lonnet::logthis('student_id = '.$student_id);
        $returnstatus = 'error: unable to insert parameters into database';
        return ($returnstatus,$student_data);
    }
    $elapsed += Time::HiRes::time - $start;
    return ($returnstatus,$student_data);
}

######################################
######################################

=pod

=item &ensure_tables_are_set_up($courseid)

Checks to be sure the MySQL tables for the given class are set up.
If $courseid is omitted it will be obtained from the environment.

Returns nothing on success and 'error' on failure

=cut

######################################
######################################
sub ensure_tables_are_set_up {
    my ($courseid) = @_;
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    # 
    # Clean out package variables
    &setup_table_names($courseid);
    #
    # if the tables do not exist, make them
    my @CurrentTable = &Apache::lonmysql::tables_in_db();
    my ($found_symb,$found_student,$found_groups,$found_groupnames,$found_part,
        $found_performance,$found_parameters,$found_fulldump_part,
        $found_fulldump_response,$found_fulldump_timestamp,
        $found_weight);
    foreach (@CurrentTable) {
        $found_symb        = 1 if ($_ eq $symb_table);
        $found_student     = 1 if ($_ eq $student_table);
        $found_groups      = 1 if ($_ eq $students_groups_table);
        $found_groupnames  = 1 if ($_ eq $groupnames_table);
        $found_part        = 1 if ($_ eq $part_table);
        $found_performance = 1 if ($_ eq $performance_table);
        $found_parameters  = 1 if ($_ eq $parameters_table);
        $found_fulldump_part      = 1 if ($_ eq $fulldump_part_table);
        $found_fulldump_response  = 1 if ($_ eq $fulldump_response_table);
        $found_fulldump_timestamp = 1 if ($_ eq $fulldump_timestamp_table);
        $found_weight      = 1 if ($_ eq $weight_table);
    }
    if (!$found_symb          || 
        !$found_student       || !$found_part              ||
        !$found_performance   || !$found_parameters        ||
        !$found_fulldump_part || !$found_fulldump_response ||
        !$found_fulldump_timestamp || !$found_weight ) {
        if (&init_dbs($courseid,1)) {
            return 'error';
        }
    }
}

################################################
################################################

=pod

=item &ensure_current_data()

Input: $sname, $sdom, $courseid

Output: $status, $data

This routine ensures the data for a given student is up to date.
The $student_table is queried to determine the time of the last update.  
If the students data is out of date, &update_student_data() is called.  
The return values from the call to &update_student_data() are returned.

=cut

################################################
################################################
sub ensure_current_data {
    my ($sname,$sdom,$courseid) = @_;
    my $status = 'okay';   # return value
    #
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    &ensure_tables_are_set_up($courseid);
    #
    # Get the update time for the user
    my $updatetime = 0;
    my $modifiedtime = &Apache::lonnet::GetFileTimestamp
        ($sdom,$sname,$courseid.'.db',
         $Apache::lonnet::perlvar{'lonUsersDir'});
    #
    if ($modifiedtime == -1) {
	return ('no data',undef);
    }

    my $student_id = &get_student_id($sname,$sdom);
    my @Result = &Apache::lonmysql::get_rows($student_table,
                                             "student_id ='$student_id'");
    my $data = undef;
    if (@Result) {
        $updatetime = $Result[0]->[6];  # Ack!  This is dumb!
    }
    if ($modifiedtime > $updatetime) {
        ($status,$data) = &update_student_data($sname,$sdom,$courseid);
    }
    return ($status,$data);
}

################################################
################################################

=pod

=item &ensure_current_full_data($sname,$sdom,$courseid)

Input: $sname, $sdom, $courseid

Output: $status

This routine ensures the fulldata (the data from a lonnet::dump, not a
lonnet::currentdump) for a given student is up to date.
The $student_table is queried to determine the time of the last update.  
If the students fulldata is out of date, &update_full_student_data() is
called.  

The return value from the call to &update_full_student_data() is returned.

=cut

################################################
################################################
sub ensure_current_full_data {
    my ($sname,$sdom,$courseid) = @_;
    my $status = 'okay';   # return value
    #
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    &ensure_tables_are_set_up($courseid);
    #
    # Get the update time for the user
    my $modifiedtime = &Apache::lonnet::GetFileTimestamp
        ($sdom,$sname,$courseid.'.db',
         $Apache::lonnet::perlvar{'lonUsersDir'});
    #
    my $student_id = &get_student_id($sname,$sdom);
    my @Result = &Apache::lonmysql::get_rows($student_table,
                                             "student_id ='$student_id'");
    my $updatetime;
    if (@Result && ref($Result[0]) eq 'ARRAY') {
        $updatetime = $Result[0]->[7];
    }
    if (! defined($updatetime) || $modifiedtime > $updatetime) {
        $status = &update_full_student_data($sname,$sdom,$courseid);
    }
    return $status;
}

################################################
################################################

=pod

=item &get_student_data_from_performance_cache()

Input: $sname, $sdom, $symb, $courseid

Output: hash reference containing the data for the given student.
If $symb is undef, all the students data is returned.

This routine is the heart of the local caching system.  See the description
of $performance_table, $symb_table, $student_table, and $part_table.  The
main task is building the MySQL request.  The tables appear in the request
in the order in which they should be parsed by MySQL.  When searching
on a student the $student_table is used to locate the 'student_id'.  All
rows in $performance_table which have a matching 'student_id' are returned,
with data from $part_table and $symb_table which match the entries in
$performance_table, 'part_id' and 'symb_id'.  When searching on a symb,
the $symb_table is processed first, with matching rows grabbed from 
$performance_table and filled in from $part_table and $student_table in
that order.  

Running 'EXPLAIN ' on the 'SELECT' statements generated can be quite 
interesting, especially if you play with the order the tables are listed.  

=cut

################################################
################################################
sub get_student_data_from_performance_cache {
    my ($sname,$sdom,$symb,$courseid)=@_;
    my $student = $sname.':'.$sdom if (defined($sname) && defined($sdom));
    &setup_table_names($courseid);
    #
    # Return hash
    my $studentdata;
    #
    my $dbh = &Apache::lonmysql::get_dbh();
    my $request = "SELECT ".
        "d.symb,a.part,a.solved,a.tries,a.awarded,a.award,a.awarddetail,".
            "a.timestamp ";
    if (defined($student)) {
        $request .= "FROM $student_table AS b ".
            "LEFT JOIN $performance_table AS a ON b.student_id=a.student_id ".
#            "LEFT JOIN $part_table AS c ON c.part_id = a.part_id ".
            "LEFT JOIN $symb_table AS d ON d.symb_id = a.symb_id ".
                "WHERE student='$student'";
        if (defined($symb) && $symb ne '') {
            $request .= " AND d.symb=".$dbh->quote($symb);
        }
    } elsif (defined($symb) && $symb ne '') {
        $request .= "FROM $symb_table as d ".
            "LEFT JOIN $performance_table AS a ON d.symb_id=a.symb_id ".
#            "LEFT JOIN $part_table    AS c ON c.part_id = a.part_id ".
            "LEFT JOIN $student_table AS b ON b.student_id = a.student_id ".
                "WHERE symb='".$dbh->quote($symb)."'";
    }
    my $starttime = Time::HiRes::time;
    my $rows_retrieved = 0;
    my $sth = $dbh->prepare($request);
    $sth->execute();
    if ($sth->err()) {
        &Apache::lonnet::logthis("Unable to execute MySQL request:");
        &Apache::lonnet::logthis("\n".$request."\n");
        &Apache::lonnet::logthis("error is:".$sth->errstr());
        return undef;
    }
    foreach my $row (@{$sth->fetchall_arrayref}) {
        $rows_retrieved++;
        my ($symb,$part,$solved,$tries,$awarded,$award,$awarddetail,$time) = 
            (@$row);
        my $base = 'resource.'.$part;
        $studentdata->{$symb}->{$base.'.solved'}  = $solved;
        $studentdata->{$symb}->{$base.'.tries'}   = $tries;
        $studentdata->{$symb}->{$base.'.awarded'} = $awarded;
        $studentdata->{$symb}->{$base.'.award'}   = $award;
        $studentdata->{$symb}->{$base.'.awarddetail'} = $awarddetail;
        $studentdata->{$symb}->{'timestamp'} = $time if (defined($time) && $time ne '');
    }
    ## Get misc parameters
    $request = 'SELECT c.symb,a.parameter,a.value '.
        "FROM $student_table AS b ".
        "LEFT JOIN $parameters_table AS a ON b.student_id=a.student_id ".
        "LEFT JOIN $symb_table AS c ON c.symb_id = a.symb_id ".
        "WHERE student='$student'";
    if (defined($symb) && $symb ne '') {
        $request .= " AND c.symb=".$dbh->quote($symb);
    }
    $sth = $dbh->prepare($request);
    $sth->execute();
    if ($sth->err()) {
        &Apache::lonnet::logthis("Unable to execute MySQL request:");
        &Apache::lonnet::logthis("\n".$request."\n");
        &Apache::lonnet::logthis("error is:".$sth->errstr());
        if (defined($symb) && $symb ne '') {
            $studentdata = $studentdata->{$symb};
        }
        return $studentdata;
    }
    #
    foreach my $row (@{$sth->fetchall_arrayref}) {
        $rows_retrieved++;
        my ($symb,$parameter,$value) = (@$row);
        $studentdata->{$symb}->{$parameter}  = $value;
    }
    #
    if (defined($symb) && $symb ne '') {
        $studentdata = $studentdata->{$symb};
    }
    return $studentdata;
}

################################################
################################################

=pod

=item &get_current_state()

Input: $sname,$sdom,$symb,$courseid

Output: Described below

Retrieve the current status of a students performance.  $sname and
$sdom are the only required parameters.  If $symb is undef the results
of an &Apache::lonnet::currentdump() will be returned.  
If $courseid is undef it will be retrieved from the environment.

The return structure is based on &Apache::lonnet::currentdump.  If
$symb is unspecified, all the students data is returned in a hash of
the form:
( 
  symb1 => { param1 => value1, param2 => value2 ... },
  symb2 => { param1 => value1, param2 => value2 ... },
)

If $symb is specified, a hash of 
(
  param1 => value1, 
  param2 => value2,
)
is returned.

If no data is found for $symb, or if the student has no performance data,
an empty list is returned.

=cut

################################################
################################################
sub get_current_state {
    my ($sname,$sdom,$symb,$courseid,$forcedownload)=@_;
    #
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    #
    return () if (! defined($sname) || ! defined($sdom));
    #
    my ($status,$data) = &ensure_current_data($sname,$sdom,$courseid);
#    &Apache::lonnet::logthis
#        ('sname = '.$sname.
#         ' domain = '.$sdom.
#         ' status = '.$status.
#         ' data is '.(defined($data)?'defined':'undefined'));
#    while (my ($symb,$hash) = each(%$data)) {
#        &Apache::lonnet::logthis($symb."\n----------------------------------");
#        while (my ($key,$value) = each (%$hash)) {
#            &Apache::lonnet::logthis("   ".$key." = ".$value);
#        }
#    }
    #
    if (defined($data) && defined($symb) && ref($data->{$symb})) {
        return %{$data->{$symb}};
    } elsif (defined($data) && ! defined($symb) && ref($data)) {
        return %$data;
    } 
    if ($status eq 'no data') {
        return ();
    } else {
        if ($status ne 'okay' && $status ne '') {
            &Apache::lonnet::logthis('status = '.$status);
            return ('error: '.$status,undef);
        }
        my $returnhash = &get_student_data_from_performance_cache($sname,$sdom,
                                                      $symb,$courseid);
        return %$returnhash if (defined($returnhash));
    }
    return ();
}

################################################
################################################

=pod

=item &get_problem_statistics()

Gather data on a given problem.  The database is assumed to be 
populated and all local caching variables are assumed to be set
properly.  This means you need to call &ensure_current_data for
the students you are concerned with prior to calling this routine.

Inputs: $Sections, Groups, $status, $symb, $part, $courseid, $starttime,
        $endtime

=over 4

=item $Sections Array ref containing section names for students.  
'all' is allowed to be the first (and only) item in the array.

=item $Groups Array ref containing group names for students.
'all' is allowed to be the first (and only) item in the array.

=item $status String describing the status of students

=item $symb is the symb for the problem.

=item $part is the part id you need statistics for

=item $courseid is the course id, of course!

=item $starttime and $endtime are unix times which to use to limit
the statistical data.

=back

Outputs: See the code for up to date information.  A hash reference is
returned.  The hash has the following keys defined:

=over 4

=item num_students The number of students attempting the problem
      
=item tries The total number of tries for the students
      
=item max_tries The maximum number of tries taken
      
=item mean_tries The average number of tries
      
=item num_solved The number of students able to solve the problem
      
=item num_override The number of students whose answer is 'correct_by_override'
      
=item deg_of_diff The degree of difficulty of the problem
      
=item std_tries The standard deviation of the number of tries
      
=item skew_tries The skew of the number of tries

=item per_wrong The number of students attempting the problem who were not
able to answer it correctly.

=back

=cut

################################################
################################################
sub get_problem_statistics {
    my ($Sections,$Groups,$status,$symb,$part,$courseid,$starttime,$endtime) = @_;
    return if (! defined($symb) || ! defined($part));
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    #
    &setup_table_names($courseid);
    my $symb_id = &get_symb_id($symb);
    my $part_id = &get_part_id($part);
    my $stats_table = &temp_table_name($courseid,'problem_stats');
    #
    my $dbh = &Apache::lonmysql::get_dbh();
    return undef if (! defined($dbh));
    #
    # Clean out the table
    $dbh->do('DROP TABLE '.$stats_table);  # May return an error
    my $request = 
        'CREATE TEMPORARY TABLE '.$stats_table.' '.
        'SELECT a.student_id,a.solved,a.award,a.awarded,a.tries '.
        'FROM '.$performance_table.' AS a ';
    #
    # See if we need to include some requirements on the students
    if ((defined($Sections) && lc($Sections->[0]) ne 'all') || 
        (defined($status)   && lc($status)        ne 'any')) {
        $request .= 'NATURAL LEFT JOIN '.$student_table.' AS b ';
    }
    my ($groups_join,$group_limits) = &limit_by_group($Groups,'b','c','d');
    if (defined($groups_join)) {
        $request .= $groups_join;
    }
    $request .= ' WHERE a.symb_id='.$symb_id.' AND a.part_id='.$part_id;
    #
    # Limit the students included to those specified
    my ($section_limits,$enrollment_limits)=
        &limit_by_section_and_status($Sections,$status,'b');
    #
    # Limit by starttime and endtime
    my $time_requirements = undef;
    if (defined($starttime)) {
        $time_requirements .= 'a.timestamp>='.$starttime;
        if (defined($endtime)) {
            $time_requirements .= ' AND a.timestamp<='.$endtime;
        }
    } elsif (defined($endtime)) {
        $time_requirements .= 'a.timestamp<='.$endtime;
    }
    if (defined($time_requirements)) {
        $request .= ' AND '.$time_requirements;
    }
    if (defined($section_limits)) {
        $request .= ' AND '.$section_limits;
    }
    if (defined($enrollment_limits)) {
        $request .= ' AND '.$enrollment_limits;
    }
    # Limit by group, as required
    if (defined($group_limits)) {
        $request .= ' AND '.$group_limits;
    }
    #
    # Finally, execute the request to create the temporary table
    $dbh->do($request);
    #
    # Collect the first suite of statistics
    $request = 'SELECT COUNT(*),SUM(tries),'.
        'AVG(tries),STD(tries) '.
        'FROM '.$stats_table;
    my ($num,$tries,$mean,$STD) = &execute_SQL_request
        ($dbh,$request);
    #
    $request = 'SELECT MAX(tries),MIN(tries) FROM '.$stats_table.
        ' WHERE awarded>0';
    if (defined($time_requirements)) {
        $request .= ' AND '.$time_requirements;
    }
    my ($max,$min) = &execute_SQL_request($dbh,$request);
    #
    $request = 'SELECT SUM(awarded) FROM '.$stats_table;
    if (defined($time_requirements)) {
        $request .= ' AND '.$time_requirements;
    }
    my ($Solved) = &execute_SQL_request($dbh,$request);
    #
    $request = 'SELECT SUM(awarded) FROM '.$stats_table.
        " WHERE solved='correct_by_override'";
    if (defined($time_requirements)) {
        $request .= ' AND '.$time_requirements;
    }
    my ($solved) = &execute_SQL_request($dbh,$request);
    #
    $Solved -= $solved;
    #
    $num    = 0 if (! defined($num));
    $tries  = 0 if (! defined($tries));
    $max    = 0 if (! defined($max));
    $min    = 0 if (! defined($min));
    $STD    = 0 if (! defined($STD));
    $Solved = 0 if (! defined($Solved) || $Solved < 0);
    $solved = 0 if (! defined($solved));
    #
    # Compute the more complicated statistics
    my $DegOfDiff = 'nan';
    $DegOfDiff = 1-($Solved)/$tries if ($tries>0);
    #
    my $SKEW = 'nan';
    my $wrongpercent = 0;
    my $numwrong = 'nan';
    if ($num > 0) {
        ($SKEW) = &execute_SQL_request($dbh,'SELECT SQRT(SUM('.
                                     'POWER(tries - '.$STD.',3)'.
                                     '))/'.$num.' FROM '.$stats_table);
        $numwrong = $num-$Solved;
        $wrongpercent=int(10*100*$numwrong/$num)/10;
    }
    #
    # Drop the temporary table
    $dbh->do('DROP TABLE '.$stats_table);  # May return an error
    #
    # Return result
    return { num_students => $num,
             tries        => $tries,
             max_tries    => $max,
             min_tries    => $min,
             mean_tries   => $mean,
             std_tries    => $STD,
             skew_tries   => $SKEW,
             num_solved   => $Solved,
             num_override => $solved,
             num_wrong    => $numwrong,
             per_wrong    => $wrongpercent,
             deg_of_diff  => $DegOfDiff };
}

##
## This is a helper for get_statistics
sub execute_SQL_request {
    my ($dbh,$request)=@_;
#    &Apache::lonnet::logthis($request);
    my $sth = $dbh->prepare($request);
    if (!$sth) {
	die($dbh->errstr . " SQL: $request");
    }
    $sth->execute();
    my $row = $sth->fetchrow_arrayref();
    if (ref($row) eq 'ARRAY' && scalar(@$row)>0) {
        return @$row;
    }
    return ();
}

######################################################
######################################################

=pod

=item &populate_weight_table

=cut

######################################################
######################################################
sub populate_weight_table {
    my ($courseid) = @_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    &setup_table_names($courseid);
    my $navmap = Apache::lonnavmaps::navmap->new();
    if (!defined($navmap)) {
        &Apache::lonnet::logthis('loncoursedata::populate_weight_table:'.$/.
                                 '  unable to get navmaps resource'.$/.
                                 '  '.join(' ',(caller)));
        return;
    }
    my @sequences = $navmap->retrieveResources(undef,
                                               sub { shift->is_map(); },1,0,1);
    my @resources;
    foreach my $seq (@sequences) {
        push(@resources,$navmap->retrieveResources($seq,
                                                   sub {shift->is_problem();},
                                                   0,0,0));
    }
    if (! scalar(@resources)) {
        &Apache::lonnet::logthis('loncoursedata::populate_weight_table:'.$/.
                                 ' no resources returned for '.$courseid);
        return;
    }
    #       Since we use lonnet::EXT to retrieve problem weights,
    #       to ensure current data we must clear the caches out.
    &Apache::lonnet::clear_EXT_cache_status();
    my $dbh = &Apache::lonmysql::get_dbh();
    my $request = 'INSERT IGNORE INTO '.$weight_table.
        "(symb_id,part_id,weight) VALUES ";
    my $weight;
    foreach my $res (@resources) {
        my $symb_id = &get_symb_id($res->symb);
        foreach my $part (@{$res->parts}) {
            my $part_id = &get_part_id($part);
            $weight = &Apache::lonnet::EXT('resource.'.$part.'.weight',
                                           $res->symb,
                                           undef,undef,undef);
            if (!defined($weight) || ($weight eq '')) { 
                $weight=1;
            }
            $request .= "('".$symb_id."','".$part_id."','".$weight."'),";
        }
    }
    $request =~ s/(,)$//;
#    &Apache::lonnet::logthis('request = '.$/.$request);
    $dbh->do($request);
    if ($dbh->err()) {
        &Apache::lonnet::logthis("error ".$dbh->errstr().
                                 " occured executing \n".
                                 $request);
    }
    return;
}

##########################################################
##########################################################

=pod

=item &limit_by_start_end_times

Build SQL WHERE condition which limits the data collected by the start
and end times provided

Inputs: $starttime, $endtime, $table

Returns: $time_limits

=cut

##########################################################
##########################################################
sub limit_by_start_end_time {
    my ($starttime,$endtime,$table) = @_;
    my $time_requirements = undef;
    if (defined($starttime)) {
        $time_requirements .= $table.".timestamp>='".$starttime."'";
        if (defined($endtime)) {
            $time_requirements .= " AND ".$table.".timestamp<='".$endtime."'";
        }
    } elsif (defined($endtime)) {
        $time_requirements .= $table.".timestamp<='".$endtime."'";
    }
    return $time_requirements;
}

##########################################################
##########################################################

=pod

=item &limit_by_section_and_status

Build SQL WHERE condition which limits the data collected by section and
student status.

Inputs: $Sections (array ref)
    $enrollment (string: 'any', 'expired', 'active')
    $tablename The name of the table that holds the student data

Returns: $student_requirements,$enrollment_requirements

=cut

##########################################################
##########################################################
sub limit_by_section_and_status {
    my ($Sections,$enrollment,$tablename) = @_;
    my $student_requirements = undef;
    if ( (defined($Sections) && $Sections->[0] ne 'all')) {
        $student_requirements = '('.
            join(' OR ', map { $tablename.".section='".$_."'" } @$Sections
                 ).')';
    }
    my $enrollment_requirements=undef;
    if (defined($enrollment) && $enrollment ne 'Any') {
	my $now = time();
	if ( $enrollment eq 'Future' ) {
	    $enrollment_requirements = 
		"( $tablename.start > $now AND ".
		"( $tablename.end = 0 OR $tablename.end > $now))";
	} elsif ( $enrollment eq 'Active' ) {
	    $enrollment_requirements = 
		"(( $tablename.start = 0 OR $tablename.start < $now )  AND ".
		" ( $tablename.end   = 0 OR $tablename.end   > $now ))";
	} elsif ( $enrollment eq 'Expired' ) {
	    $enrollment_requirements = 
		"(( $tablename.start < $now )  AND ".
		" ( $tablename.end   < $now ))";
	}
    }
    return ($student_requirements,$enrollment_requirements);
}

######################################################
######################################################
                                                                               
=pod
                                                                               
=item &limit_by_group
                                                                               
Build SQL LEFT JOIN statement to include students_groups and groupnames tables and SQL WHERE condition which limits the data collected by group.
                                                                               
Inputs: $Groups (array ref)
    $stutable   The name of the table which holds the student data.
    $grptable   The name of the table which maps group_id to groupname.
    $stugrptab  The name of the table which holds student group affiliations.   
Returns: $groups_join,$group_limits
   $groups_join  JOIN part of SQL statement (to include group related tables) 
   $group_limits SQL WHERE condition limiting to requested groups
=cut

sub limit_by_group {
    my ($Groups,$stutable,$grptable,$stugrptab) = @_;
    my $groups_join = undef;
    my $group_limits = undef;
    if ( (defined($Groups) && $Groups->[0] ne 'all')) {
        $groups_join =
          ' LEFT JOIN '.$students_groups_table.
                     ' AS '.$stugrptab.' ON '.
                     $stugrptab.'.student_id = '.$stutable.'.student_id'.
          ' LEFT JOIN '.$groupnames_table.
                     ' AS '.$grptable.' ON '.
                     $stugrptab.'.group_id = '.$grptable.'.group_id ';
        $group_limits =
          ' ('.
             join(' OR ', map {  "$grptable.groupname='".$_."'" } @$Groups
           ).')';
    }
    return ($groups_join,$group_limits);
}

=pod

=item rank_students_by_scores_on_resources

Inputs: 
    $resources: array ref of hash ref.  Each hash ref needs key 'symb'.
    $Sections: array ref of sections to include,
    $Groups: array ref of groups to include.
    $enrollment: string,
    $courseid (may be omitted)
    $starttime (may be omitted)
    $endtime (may be omitted)
    $has_award_for (may be omitted)

Returns; An array of arrays.  The sub arrays contain a student name and
their score on the resources. $starttime and $endtime constrain the
list to awards obtained during the given time limits. $has_score_on
constrains the list to those students who at least attempted the
resource identified by the given symb, which is used to filter out
such students for statistics that would be adversely affected by such
students. 

=cut

######################################################
######################################################
sub RNK_student { return 0; };
sub RNK_score   { return 1; };

sub rank_students_by_scores_on_resources {
    my ($resources,$Sections,$Groups,$enrollment,$courseid,$starttime,$endtime,
        $has_award_for) = @_;
    return if (! defined($resources) || ! ref($resources) eq 'ARRAY');
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    &setup_table_names($courseid);
    my $dbh = &Apache::lonmysql::get_dbh();
    my ($section_limits,$enrollment_limits)=
        &limit_by_section_and_status($Sections,$enrollment,'b');
    my ($groups_join,$group_limits) = &limit_by_group($Groups,'b','c','d');
    my $symb_limits = '('.join(' OR ',map {'a.symb_id='.&get_symb_id($_);
                                       } @$resources
                               ).')';
    my ($award_col, $award_join, $award_clause) = ('', '', '');
    if ($has_award_for) {
        my $resource_id = &get_symb_id($has_award_for);
        $award_col = ", perf.awarded";
        $award_join = "LEFT JOIN $performance_table AS perf ON perf.symb_id"
            ." = $resource_id AND perf.student_id = b.student_id ";
        $award_clause = "AND perf.awarded IS NOT NULL";
    }
    my $time_limits = &limit_by_start_end_time($starttime,$endtime,'a');
    my $request = "SELECT b.student,SUM(a.awarded*w.weight) AS score "
        ."$award_col FROM $performance_table AS a ".
        "NATURAL LEFT JOIN $weight_table AS w ".
        "LEFT JOIN $student_table AS b ON a.student_id=b.student_id ".
        "$award_join $groups_join "; 
    my $limits;
    if (defined($section_limits)) {
        $limits .= $section_limits.' AND ';
    }
    if (defined($enrollment_limits)) {
        $limits .= $enrollment_limits.' AND ';
    }
    if (defined($time_limits)) {
        $limits .= $time_limits.' AND ';
    }
    if ($symb_limits ne '()') {
        $limits .= $symb_limits.' AND ';
    }
    if (defined($group_limits)) {
        $limits .= $group_limits.' AND ';
    }
    if ($limits) {
        $limits =~ s/( AND )$//;   # Remove extra conjunction
        $request .= "WHERE $limits";
    } 
    $request .= " $award_clause GROUP BY a.student_id ORDER BY score";
    #&Apache::lonnet::logthis('request = '.$/.$request);
    my $sth = $dbh->prepare($request) or die "Can't prepare $request";
    $sth->execute();
    my $rows = $sth->fetchall_arrayref();
    return ($rows);
}

########################################################
########################################################

=pod

=item &get_sum_of_scores

Inputs: $resource (hash ref, needs {'symb'} key),
$part, (the part id),
$students (array ref, contents of array are scalars holding 'sname:sdom'),
$courseid

Returns: the sum of the score on the problem part over the students and the
   maximum possible value for the sum (taken from the weight table).

=cut

########################################################
########################################################
sub get_sum_of_scores {
    my ($symb,$part,$students,$courseid,$starttime,$endtime) = @_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    if (defined($students) && 
        ((@$students == 0) ||
         (@$students == 1 && (! defined($students->[0]) || 
                              $students->[0] eq ''))
         )
        ){
        undef($students);
    }
    #
    &setup_table_names($courseid);
    my $dbh = &Apache::lonmysql::get_dbh();
    my $time_limits = &limit_by_start_end_time($starttime,$endtime,'a');
    my $request = 'SELECT SUM(a.awarded*w.weight),SUM(w.weight) FROM '.
        $performance_table.' AS a '.
        'NATURAL LEFT JOIN '.$weight_table.' AS w ';
    $request .= 'WHERE a.symb_id='.&get_symb_id($symb).
        ' AND a.part_id='.&get_part_id($part);
    if (defined($time_limits)) {
        $request .= ' AND '.$time_limits;
    }
    if (defined($students)) {
        $request .= ' AND ('.
            join(' OR ',map {'a.student_id='.&get_student_id(split(':',$_));
                         } @$students).
                             ')';
    }
    my $sth = $dbh->prepare($request);
    $sth->execute();
    my $rows = $sth->fetchrow_arrayref();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 1 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed, fetchrow_arrayrefed'.
                                 $/.$request);
        return (undef,undef);
    }
    return ($rows->[0],$rows->[1]);
}

########################################################
########################################################

=pod

=item &score_stats

Inputs: $Sections, $enrollment, $symbs, $starttime,
        $endtime, $courseid

$Sections, $enrollment, $starttime, $endtime, and $courseid are the same as 
elsewhere in this module.  
$symbs is an array ref of symbs

Returns: minimum, maximum, mean, s.d., number of students, and maximum
  possible of student scores on the given resources

=cut

########################################################
########################################################
sub score_stats {
    my ($Sections,$Groups,$enrollment,$symbs,$starttime,$endtime,$courseid)=@_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    &setup_table_names($courseid);
    my $dbh = &Apache::lonmysql::get_dbh();
    #
    my ($section_limits,$enrollment_limits)=
        &limit_by_section_and_status($Sections,$enrollment,'b');
    my ($groups_join,$group_limits) = &limit_by_group($Groups,'b','c','d');
    my $time_limits = &limit_by_start_end_time($starttime,$endtime,'a');
    my @Symbids = map { &get_symb_id($_); } @{$symbs};
    #
    my $stats_table = &temp_table_name($courseid,'problem_stats');
    my $symb_restriction = join(' OR ',map {'a.symb_id='.$_;} @Symbids);
    my $request = 'DROP TABLE '.$stats_table;
    $dbh->do($request);
    $request = 
        'CREATE TEMPORARY TABLE '.$stats_table.' '.
        'SELECT a.student_id,'.
        'SUM(a.awarded*w.weight) AS score FROM '.
        $performance_table.' AS a '.
        'NATURAL LEFT JOIN '.$weight_table.' AS w '.
        'LEFT JOIN '.$student_table.' AS b ON a.student_id=b.student_id '.
        $groups_join;
    my $limit = ' WHERE ('.$symb_restriction.')';
    if ($time_limits) {
        $limit .= ' AND '.$time_limits;
    }
    if ($section_limits) {
        $limit .= ' AND '.$section_limits;
    }
    if ($enrollment_limits) {
        $limit .= ' AND '.$enrollment_limits;
    }
    if ($group_limits) {
        $limit .= ' AND '.$group_limits;
    }
    $request .= $limit.' GROUP BY a.student_id';
#    &Apache::lonnet::logthis('request = '.$/.$request);
    my $sth = $dbh->prepare($request);
    $sth->execute();
    $request = 
        'SELECT AVG(score),STD(score),MAX(score),MIN(score),COUNT(score) '.
        'FROM '.$stats_table;
    my ($ave,$std,$max,$min,$count) = &execute_SQL_request($dbh,$request);
#    &Apache::lonnet::logthis('request = '.$/.$request);
    
    $request = 'SELECT SUM(weight) FROM '.$weight_table.
        ' AS a WHERE ('.$symb_restriction.')';
    my ($max_possible) = &execute_SQL_request($dbh,$request);
    # &Apache::lonnet::logthis('request = '.$/.$request);
    return($min,$max,$ave,$std,$count,$max_possible);
}


########################################################
########################################################

=pod

=item &count_stats

Inputs: $Sections, $Groups, $enrollment, $symbs, $starttime,
        $endtime, $courseid

$Sections, $Groups $enrollment, $starttime, $endtime, and $courseid are the 
same as elsewhere in this module.  
$symbs is an array ref of symbs

Returns: minimum, maximum, mean, s.d., and number of students
  of the number of items correct on the given resources

=cut

########################################################
########################################################
sub count_stats {
    my ($Sections,$Groups,$enrollment,$symbs,$starttime,$endtime,$courseid)=@_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    &setup_table_names($courseid);
    my $dbh = &Apache::lonmysql::get_dbh();
    #
    my ($section_limits,$enrollment_limits)=
        &limit_by_section_and_status($Sections,$enrollment,'b');
    my ($groups_join,$group_limits) = &limit_by_group($Groups,'b','c','d');
    my $time_limits = &limit_by_start_end_time($starttime,$endtime,'a');
    my @Symbids = map { &get_symb_id($_); } @{$symbs};
    #
    my $stats_table = &temp_table_name($courseid,'problem_stats');
    my $symb_restriction = join(' OR ',map {'a.symb_id='.$_;} @Symbids);
    my $request = 'DROP TABLE '.$stats_table;
    $dbh->do($request);
    $request = 
        'CREATE TEMPORARY TABLE '.$stats_table.' '.
        'SELECT a.student_id,'.
        'SUM(a.awarded) AS count FROM '.
        $performance_table.' AS a '.
        'LEFT JOIN '.$student_table.' AS b ON a.student_id=b.student_id '.
        $groups_join;
    my $limit =  ' WHERE ('.$symb_restriction.')';
    if ($time_limits) {
        $limit .= ' AND '.$time_limits;
    }
    if ($section_limits) {
        $limit .= ' AND '.$section_limits;
    }
    if ($enrollment_limits) {
        $limit .= ' AND '.$enrollment_limits;
    }
    if ($group_limits) {
        $limit .= ' AND '.$group_limits;
    }
    $request .= $limit.' GROUP BY a.student_id';
#    &Apache::lonnet::logthis('request = '.$/.$request);
    my $sth = $dbh->prepare($request);
    $sth->execute();
    $request = 
        'SELECT AVG(count),STD(count),MAX(count),MIN(count),COUNT(count) '.
        'FROM '.$stats_table;
    my ($ave,$std,$max,$min,$count) = &execute_SQL_request($dbh,$request);
#    &Apache::lonnet::logthis('request = '.$/.$request);
    return($min,$max,$ave,$std,$count);
}

######################################################
######################################################

=pod

=item get_student_data

=cut

######################################################
######################################################
sub get_student_data {
    my ($students,$courseid) = @_;
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    &setup_table_names($courseid);
    my $dbh = &Apache::lonmysql::get_dbh();
    return undef if (! defined($dbh));
    my $request = 'SELECT '.
        'student_id, student '.
        'FROM '.$student_table;
    if (defined($students)) {
        $request .= ' WHERE ('.
            join(' OR ', map {'student_id='.
                                  &get_student_id($_->{'username'},
                                                  $_->{'domain'})
                              } @$students
                 ).')';
    }
    $request.= ' ORDER BY student_id';
    my $sth = $dbh->prepare($request);
    $sth->execute();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 2 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed '.$/.$request);
        return undef;
    }
    my $dataset = $sth->fetchall_arrayref();
    if (ref($dataset) eq 'ARRAY' && scalar(@$dataset)>0) {
        return $dataset;
    }
}

sub RD_student_id      { return 0; }
sub RD_awarddetail     { return 1; }
sub RD_response_eval   { return 2; }
sub RD_response_eval_2 { return 3; }
sub RD_submission      { return 4; }
sub RD_timestamp       { return 5; }
sub RD_tries           { return 6; }
sub RD_sname           { return 7; }

sub get_response_data {
    my ($Sections,$Groups,$enrollment,$symb,$response,$courseid) = @_;
    return undef if (! defined($symb) || 
               ! defined($response));
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    #
    &setup_table_names($courseid);
    my $symb_id = &get_symb_id($symb);
    if (! defined($symb_id)) {
        &Apache::lonnet::logthis('Unable to find symb for '.$symb.' in '.$courseid);
        return undef;
    }
    my $response_id = &get_part_id($response);
    if (! defined($response_id)) {
        &Apache::lonnet::logthis('Unable to find id for '.$response.' in '.$courseid);
        return undef;
    }
    #
    my $dbh = &Apache::lonmysql::get_dbh();
    return undef if (! defined($dbh));
    #
    my ($student_requirements,$enrollment_requirements) = 
        &limit_by_section_and_status($Sections,$enrollment,'d');
    my ($groups_join,$group_limits) = &limit_by_group($Groups,'d','e','f');
    my $request = 'SELECT '.
        'a.student_id, a.awarddetail, a.response_specific_value, '.
        'a.response_specific_value_2, a.submission, b.timestamp, '.
	'c.tries, d.student '.
        'FROM '.$fulldump_response_table.' AS a '.
        'LEFT JOIN '.$fulldump_timestamp_table.' AS b '.
        'ON a.symb_id=b.symb_id AND a.student_id=b.student_id AND '.
        'a.transaction = b.transaction '.
        'LEFT JOIN '.$fulldump_part_table.' AS c '.
        'ON a.symb_id=c.symb_id AND a.student_id=c.student_id AND '.        
        'a.part_id=c.part_id AND a.transaction = c.transaction '.
        'LEFT JOIN '.$student_table.' AS d '.
        'ON a.student_id=d.student_id '.
        $groups_join;
    my $limit = ' WHERE '.
        'a.symb_id='.$symb_id.' AND a.response_id='.$response_id;
    if (defined($student_requirements)) {
        $limit .= ' AND '.$student_requirements;
    }
    if (defined($enrollment_requirements)) {
        $limit .= ' AND '.$enrollment_requirements;
    }
    if (defined($group_limits)) {
        $limit .= ' AND '.$group_limits;
    }
    $request .= $limit.' ORDER BY b.timestamp';
#    &Apache::lonnet::logthis("request =\n".$request);
    my $sth = $dbh->prepare($request);
    $sth->execute();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 3 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed '.$/.$request);
        return undef;
    }
    my $dataset = $sth->fetchall_arrayref();
    if (ref($dataset) eq 'ARRAY' && scalar(@$dataset)>0) {
        # Clear the \'s from around the submission
        for (my $i =0;$i<scalar(@$dataset);$i++) {
            $dataset->[$i]->[&RD_submission()] =~ s/(\'$|^\')//g;
        }
        return $dataset;
    }
}


sub RDs_awarddetail     { return 3; }
sub RDs_submission      { return 2; }
sub RDs_timestamp       { return 1; }
sub RDs_tries           { return 0; }
sub RDs_awarded         { return 4; }
sub RDs_response_eval   { return 5; }
sub RDs_response_eval_2 { return 6; }
sub RDs_part_award      { return 7; }

sub get_response_data_by_student {
    my ($student,$symb,$response,$courseid) = @_;
    return undef if (! defined($symb) || 
                     ! defined($response));
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    #
    &setup_table_names($courseid);
    my $symb_id = &get_symb_id($symb);
    my $response_id = &get_part_id($response);
    #
    my $student_id = &get_student_id($student->{'username'},
                                     $student->{'domain'});
    #
    my $dbh = &Apache::lonmysql::get_dbh();
    return undef if (! defined($dbh));
    my $request = 'SELECT '.
        'c.tries, b.timestamp, a.submission, a.awarddetail, c.awarded, '.
	'a.response_specific_value, a.response_specific_value_2, c.award '.
        'FROM '.$fulldump_response_table.' AS a '.
        'LEFT JOIN '.$fulldump_timestamp_table.' AS b '.
        'ON a.symb_id=b.symb_id AND a.student_id=b.student_id AND '.
        'a.transaction = b.transaction '.
        'LEFT JOIN '.$fulldump_part_table.' AS c '.
        'ON a.symb_id=c.symb_id AND a.student_id=c.student_id AND '.        
        'a.part_id=c.part_id AND a.transaction = c.transaction '.
        'LEFT JOIN '.$student_table.' AS d '.
        'ON a.student_id=d.student_id '.
        'LEFT JOIN '.$performance_table.' AS e '.
        'ON a.symb_id=e.symb_id AND a.part_id=e.part_id AND '.
        'a.student_id=e.student_id AND c.tries=e.tries '.
        'WHERE '.
        'a.symb_id='.$symb_id.' AND a.response_id='.$response_id.
        ' AND a.student_id='.$student_id.' ORDER BY b.timestamp';
#    &Apache::lonnet::logthis("request =\n".$request);
    my $sth = $dbh->prepare($request);
    $sth->execute();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 4 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed '.$/.$request);
        return undef;
    }
    my $dataset = $sth->fetchall_arrayref();
    if (ref($dataset) eq 'ARRAY' && scalar(@$dataset)>0) {
        # Clear the \'s from around the submission
        for (my $i =0;$i<scalar(@$dataset);$i++) {
            $dataset->[$i]->[&RDs_submission] =~ s/(\'$|^\')//g;
        }
        return $dataset;
    }
    return undef; # error occurred
}

sub RT_student_id { return 0; }
sub RT_awarded    { return 1; }
sub RT_tries      { return 2; }
sub RT_timestamp  { return 3; }

sub get_response_time_data {
    my ($sections,$groups,$enrollment,$symb,$part,$courseid) = @_;
    return undef if (! defined($symb) || 
                     ! defined($part));
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    #
    &setup_table_names($courseid);
    my $symb_id = &get_symb_id($symb);
    if (! defined($symb_id)) {
        &Apache::lonnet::logthis('Unable to find symb for '.$symb.' in '.$courseid);
        return undef;
    }
    my $part_id = &get_part_id($part);
    if (! defined($part_id)) {
        &Apache::lonnet::logthis('Unable to find id for '.$part.' in '.$courseid);
        return undef;
    }
    #
    my $dbh = &Apache::lonmysql::get_dbh();
    return undef if (! defined($dbh));
    my ($student_requirements,$enrollment_requirements) = 
        &limit_by_section_and_status($sections,$enrollment,'d');
    my ($groups_join,$group_limits) = &limit_by_group($groups,'d','e','f');
    my $request = 'SELECT '.
        'a.student_id, a.awarded, a.tries, b.timestamp '.
        'FROM '.$fulldump_part_table.' AS a '.
        'LEFT JOIN '.$fulldump_timestamp_table.' AS b '.
        'ON a.symb_id=b.symb_id AND a.student_id=b.student_id AND '.
        'a.transaction = b.transaction '.
        'LEFT JOIN '.$student_table.' as d '.
        'ON a.student_id=d.student_id '.
        $groups_join;
    my $limit = ' WHERE '.
        'a.symb_id='.$symb_id.' AND a.part_id='.$part_id;
    if (defined($student_requirements)) {
        $limit .= ' AND '.$student_requirements;
    }
    if (defined($enrollment_requirements)) {
        $limit .= ' AND '.$enrollment_requirements;
    }
    if (defined($group_limits)) {
        $limit .= ' AND '.$group_limits;  
    }
    $request .= $limit.' ORDER BY b.timestamp';
#    &Apache::lonnet::logthis("request =\n".$request);
    my $sth = $dbh->prepare($request);
    $sth->execute();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 5 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed '.$/.$request);
        return undef;
    }
    my $dataset = $sth->fetchall_arrayref();
    if (ref($dataset) eq 'ARRAY' && scalar(@$dataset)>0) {
        return $dataset;
    }

}

################################################
################################################

=pod

=item &get_student_scores($Sections,$Groups,$Symbs,$enrollment,$courseid)

=cut

################################################
################################################
sub get_student_scores {
    my ($sections,$groups,$Symbs,$enrollment,$courseid,$starttime,$endtime) = @_;
    $courseid = $env{'request.course.id'} if (! defined($courseid));
    &setup_table_names($courseid);
    my $dbh = &Apache::lonmysql::get_dbh();
    return (undef) if (! defined($dbh));
    my $tmptable = &temp_table_name($courseid,'temp_'.time);
    my $request = 'DROP TABLE IF EXISTS '.$tmptable;
#    &Apache::lonnet::logthis('request = '.$/.$request);
    $dbh->do($request);
    #
    my $symb_requirements;
    if (defined($Symbs)  && @$Symbs) {
        $symb_requirements = '('.
            join(' OR ', map{ "(a.symb_id='".&get_symb_id($_->{'symb'}).
                              "' AND a.part_id='".&get_part_id($_->{'part'}).
                              "')"
                              } @$Symbs).')';
    }
    #
    my ($student_requirements,$enrollment_requirements) = 
        &limit_by_section_and_status($sections,$enrollment,'b');
    #
    my ($groups_join,$group_limits) = &limit_by_group($groups,'b','d','e');
    my $time_requirements = &limit_by_start_end_time($starttime,$endtime,'a');
    ##
    $request = 'CREATE TEMPORARY TABLE IF NOT EXISTS '.$tmptable.
        ' SELECT a.student_id,SUM(a.awarded*c.weight) AS score FROM '.
        $performance_table.' AS a ';
    $request .= "LEFT JOIN ".$weight_table.' AS c ON a.symb_id=c.symb_id AND a.part_id=c.part_id ';
    if (defined($student_requirements) || defined($enrollment_requirements)) {
        $request .= ' LEFT JOIN '.$student_table.' AS b ON a.student_id=b.student_id ';
    }
    if (defined($groups_join)) {
        $request .= $groups_join;
    }
    if (defined($symb_requirements)       || 
        defined($student_requirements)    ||
        defined($enrollment_requirements) ||
        defined($group_limits) ) {
        $request .= ' WHERE ';
    }
    if (defined($symb_requirements)) {
        $request .= $symb_requirements.' AND ';
    }
    if (defined($student_requirements)) {
        $request .= $student_requirements.' AND ';
    }
    if (defined($enrollment_requirements)) {
        $request .= $enrollment_requirements.' AND ';
    }
    if (defined($time_requirements)) {
        $request .= $time_requirements.' AND ';
    }
    $request =~ s/ AND $//; # Strip of the trailing ' AND '.
    $request .= ' GROUP BY a.student_id';
#    &Apache::lonnet::logthis("request = \n".$request);
    my $sth = $dbh->prepare($request);
    $sth->execute();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 6 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed '.$/.$request);
        return undef;
    }
    $request = 'SELECT score,COUNT(*) FROM '.$tmptable.' GROUP BY score';
#    &Apache::lonnet::logthis("request = \n".$request);
    $sth = $dbh->prepare($request);
    $sth->execute();
    if ($dbh->err) {
        &Apache::lonnet::logthis('error 7 = '.$dbh->errstr());
        &Apache::lonnet::logthis('prepared then executed '.$/.$request);
        return undef;
    }
    my $dataset = $sth->fetchall_arrayref();
    return $dataset;
}

################################################
################################################

=pod

=item &setup_table_names()

input: course id

output: none

Cleans up the package variables for local caching.

=cut

################################################
################################################
sub setup_table_names {
    my ($courseid) = @_;
    if (! defined($courseid)) {
        $courseid = $env{'request.course.id'};
    }
    #
    if (! defined($current_course) || $current_course ne $courseid) {
        # Clear out variables
        $have_read_part_table = 0;
        undef(%ids_by_part);
        undef(%parts_by_id);
        $have_read_symb_table = 0;
        undef(%ids_by_symb);
        undef(%symbs_by_id);
        $have_read_student_table = 0;
        undef(%ids_by_student);
        undef(%students_by_id);
        $have_read_groupnames_table = 0;
        undef(%ids_by_groupname);
        #
        $current_course = $courseid;
    }
    #
    # Set up database names
    my $base_id = 'md5_'.&Digest::MD5::md5_hex($courseid);
    $symb_table               = $base_id.'_'.'symb';
    $part_table               = $base_id.'_'.'part';
    $student_table            = $base_id.'_'.'student';
    $groupnames_table         = $base_id.'_'.'groupnames';
    $students_groups_table    = $base_id.'_'.'studentgroups';
    $performance_table        = $base_id.'_'.'performance';
    $parameters_table         = $base_id.'_'.'parameters';
    $fulldump_part_table      = $base_id.'_'.'partdata';
    $fulldump_response_table  = $base_id.'_'.'responsedata';
    $fulldump_timestamp_table = $base_id.'_'.'timestampdata';
    $weight_table             = $base_id.'_'.'weight';
    #
    @Tables = (
               $symb_table,
               $part_table,
               $student_table,
               $groupnames_table,
               $students_groups_table,
               $performance_table,
               $parameters_table,
               $fulldump_part_table,
               $fulldump_response_table,
               $fulldump_timestamp_table,
               $weight_table,
               );
    return;
}

sub temp_table_name {
    my ($courseid,$affix) = @_;
    my $base_id = 'md5_'.&Digest::MD5::md5_hex($courseid);
    return $base_id.'_'.$affix;
}

################################################
################################################

=pod

=back

=item End of Local Data Caching Subroutines

=cut

################################################
################################################

} # End scope of table identifiers

################################################
################################################

=pod

=head3 Classlist Subroutines

=item &get_classlist();

Retrieve the classist of a given class or of the current class.  Student
information is returned from the classlist.db file and, if needed,
from the students environment.

Optional arguments are $cdom, and $cnum (course domain,
and course number, respectively).  If either is ommitted the course
will be taken from the current environment ($env{'request.course.id'},
$env{'course.'.$cid.'.domain'}, and $env{'course.'.$cid.'.num'}).

Returns a reference to a hash which contains:
 keys    '$sname:$sdom'
 values  [$sdom,$sname,$end,$start,$id,$section,$fullname,$status,$type,$lockedtype]

The constant values CL_SDOM, CL_SNAME, CL_END, etc. can be used
as indices into the returned list to future-proof clients against
changes in the list order.

=cut

################################################
################################################

sub CL_SDOM     { return 0; }
sub CL_SNAME    { return 1; }
sub CL_END      { return 2; }
sub CL_START    { return 3; }
sub CL_ID       { return 4; }
sub CL_SECTION  { return 5; }
sub CL_FULLNAME { return 6; }
sub CL_STATUS   { return 7; }
sub CL_TYPE     { return 8; }
sub CL_LOCKEDTYPE   { return 9; }

sub get_classlist {
    my ($cdom,$cnum) = @_;
    my $cid = $cdom.'_'.$cnum;
    if (!defined($cdom) || !defined($cnum)) {
	$cid =  $env{'request.course.id'};
	$cdom = $env{'course.'.$cid.'.domain'};
	$cnum = $env{'course.'.$cid.'.num'};
    }
    my $now = time;
    #
    my %classlist=&Apache::lonnet::dump('classlist',$cdom,$cnum);
    while (my ($student,$info) = each(%classlist)) {
        if ($student =~ /^(con_lost|error|no_such_host)/i) {
            &Apache::lonnet::logthis('get_classlist error for '.$cid.':'.$student);
            return undef;
        }
        my ($sname,$sdom) = split(/:/,$student);
        my @Values = split(/:/,$info);
        my ($end,$start,$id,$section,$fullname,$type,$lockedtype);
        if (@Values > 2) {
            ($end,$start,$id,$section,$fullname,$type,$lockedtype) = @Values;
        } else { # We have to get the data ourselves
            ($end,$start) = @Values;
            $section = &Apache::lonnet::getsection($sdom,$sname,$cid);
            my %info=&Apache::lonnet::get('environment',
                                          ['firstname','middlename',
                                           'lastname','generation','id'],
                                          $sdom, $sname);
            my ($tmp) = keys(%info);
            if ($tmp =~/^(con_lost|error|no_such_host)/i) {
                $fullname = 'not available';
                $id = 'not available';
                &Apache::lonnet::logthis('unable to retrieve environment '.
                                         'for '.$sname.':'.$sdom);
            } else {
                $fullname = &Apache::lonnet::format_name(@info{qw/firstname middlename lastname generation/},'lastname');
                $id = $info{'id'};
            }
            # Update the classlist with this students information
            if ($fullname ne 'not available') {
		my $enrolldata = join(':',$end,$start,$id,$section,$fullname);
		my $reply=&Apache::lonnet::cput('classlist',
                                                {$student => $enrolldata},
                                                $cdom,$cnum);
                if ($reply !~ /^(ok|delayed)/) {
                    &Apache::lonnet::logthis('Unable to update classlist for '.
                                             'student '.$sname.':'.$sdom.
                                             ' error:'.$reply);
                }
            }
        }
        my $status='Expired';
        if(((!$end) || $now < $end) && ((!$start) || ($now > $start))) {
            $status='Active';
        }
        if(($now < $start) && ((!$end) || $now < $end )) {
            $status='Future';
        }
        $classlist{$student} = 
            [$sdom,$sname,$end,$start,$id,$section,$fullname,$status,$type,$lockedtype];
    }
    if (wantarray()) {
        return (\%classlist,['domain','username','end','start','id',
                             'section','fullname','status','type','lockedtype']);
    } else {
        return \%classlist;
    }
}

sub get_group_memberships {
    my ($classlist,$keylist,$cdom,$cnum) = @_;

    return ({},{}) if (!ref($classlist) || !ref($keylist));

    my $cid = $cdom.'_'.$cnum;
    if (!defined($cdom) || !defined($cnum)) {
        $cid =  $env{'request.course.id'};
        $cdom = $env{'course.'.$cid.'.domain'};
        $cnum = $env{'course.'.$cid.'.num'};
    }
    my (%classgroups,%studentgroups);
    my $now = time;
    my $access_end = $env{'course.'.$cid.'.default_enrollment_end_date'};
    my %curr_groups =&Apache::longroup::coursegroups($cdom,$cnum);
    if (%curr_groups) {
        my $grpindex = scalar(@{$keylist});
        my %groupmemberhash = 
	    &Apache::lonnet::get_group_membership($cdom,$cnum);
        foreach my $student (keys(%{$classlist})) {
            %{$classgroups{$student}} = ();
            my $hasgroup = 0;
            foreach my $status ('previous','future','active','aftercourse') {
                %{$classgroups{$student}{$status}} = ();
            }
            foreach my $group (keys(%curr_groups)) {
                if (defined($groupmemberhash{$group.':'.$student})) {
                    my ($end,$start) = split(/:/,$groupmemberhash{$group.':'.
                                                                    $student});
                    if ($start == -1) {
                        next;
                    } else {
                        $studentgroups{$group} ++;
                        $hasgroup = 1;
                        if ($end && $end < $now) {
                            $classgroups{$student}{'previous'}{$group} =
                                         $groupmemberhash{$group.':'.$student};
                            if ($classlist->{$student}[&CL_STATUS()] eq 'Expired') {
                                if ($access_end && $access_end < $now) {
                                    if ($access_end - $end < 86400) {
                                        $classgroups{$student}{'aftercourse'}{$group} = $groupmemberhash{$group.':'.$student};
                                    }
                                }
                            }
                        } elsif ($now > $start) {
                            if (!$end || $end > $now) {
                                $classgroups{$student}{'active'}{$group} =
                                         $groupmemberhash{$group.':'.$student};
                            }
                        } else {
                            $classgroups{$student}{'future'}{$group} =
                                         $groupmemberhash{$group.':'.$student};
                        }
                    }
                }
            }
            if (!$hasgroup) {
                $studentgroups{'none'} ++;
            } else {
                $classlist->{$student}->[$grpindex] = join(',',
                              sort(keys(%{$classgroups{$student}{'active'}})));
            }
        }
    }
    return (\%classgroups,\%studentgroups);
}
                                                                                   
sub get_students_groups {
    my ($student,$enrollment_status,$classgroups) = @_;
    my @studentsgroups = ();
    if (ref($$classgroups{$student}{'active'}) eq 'HASH') {
        push(@studentsgroups,keys(%{$$classgroups{$student}{'active'}}));
    }
    if ($enrollment_status eq 'Any') {
        foreach my $status ('previous','future') {
            if (ref($$classgroups{$student}{$status}) eq 'HASH') {
                push(@studentsgroups,keys(%{$$classgroups{$student}{$status}}));
            }
        }
    } else {
        if (ref($$classgroups{$student}{'aftercourse'}) eq 'HASH') {
            push(@studentsgroups,keys(%{$$classgroups{$student}{'aftercourse'}}));
        }
    }
    return @studentsgroups;
}


# ----- END HELPER FUNCTIONS --------------------------------------------

1;
__END__


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