Aggregate(3pm)

NAME
Lire::Aggregate - Base class for all operators that compute values from a group of DLF records

SYNOPSIS
    use Lire::Aggregate;

    use base qw/ Lire::Aggregate /;

DESCRIPTION
The Lire::Aggregate is the base class of all operators that computes values from a group of DLF records. These are the operators that are used inside aggregators.

This package also defines most of the classes that represents the group operators available in Lire report specification.

METHODS FOR SUBCLASSES OF Aggregate

  init( %params )
Two supplemental parameters are needed for Aggregates:

parent
    The Lire::Aggregator which contain this Aggregate.

name
    The identifier that can be used to find this operator in the report specification. It will be returned by the name() method.

  print( $fh, $prefix)
This methods implements the print() method required by Lire::ReportOperator. It prints an empty XML element named after op(). It also takes care of writing the name and label attributes. Other attributes can be added to the XML element by overriding the xml_attrs() method.

  xml_attrs()
This method can be used to write additional XML attributes. The returned string will be output in the XML element.

  set_name( $name )
Changes this operator's name.

  create_numerical_info( $group_info )
Subclass must implement this method.

The $group_info parameter is a Lire::Report::GroupInfo object to which the operator implementation should add the appropriate ColumnInfo object to represent the data generated by the aggregate.

  build_query( $query )
FIXME.

Provides a default implementation of build_query

  set_missing_cases_aggr_expr( $query )
Adds the aggregate expression to compute the number of missing cases based on the required fields returned by the sql_required_fields() method.

The method set_missing_cases_value() can be used to set the value from the returned DLF row.

  set_missing_cases_value( $row, $value )
Sets the missing-cases value in $value to the value computed by the expression sets using set_missing_cases_aggr_expr().

  sql_aggr_expr()
Method used by the default implementation of build_query(). It should return the SQL agregate expression that should be associated to this Aggregate's name. For example, a simple Count implementation could have returned 'count(*)' here.

  sql_required_fields()
Method used by the set_missing_cases_aggr_expr() to sets an aggregate expression that will return the number of missing cases for this aggregate. It should returns a list of fields that will create a missing case when a value is NULL.

  create_value( $parent_group, $row )
Method that is used by Aggregator when building the report table. The report should return an hash reference with the appropriate keys set. Consult Lire::Report::Entry(3pm) for details.

The $parent_group parameter is the Lire::Report::Group to which the value is added. This will be the table or containing group for values added to Entries, and it will be the Group's parent when creating a summary value.

The $row parameter is an hash ref containing the DlfResult row for which the value should be created.

Implementation should use the set_missing_cases_value() method to set the value's 'missing_cases' attribute.

SEE ALSO
Lire::ReportSpec(3pm), Lire::ReportOperator(3pm), Lire::Aggregator(3pm).

AUTHORS
  Francis J. Lacoste <flacoste@logreport.org>
  Wolfgang Sourdeau <wolfgang@logreport.org>

VERSION
$Id: Aggregate.pm,v 1.16 2006/07/23 13:16:27 vanbaal Exp $

COPYRIGHT
Copyright (C) 2001-2003 Stichting LogReport Foundation LogReport@LogReport.org

This file is part of Lire.

Lire 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.

This program 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 this program (see COPYING); if not, check with http://www.gnu.org/copyleft/gpl.html.