Aaron James Trevena > Class-DBI-Relationship-IsA > Class::DBI::Relationship::IsA

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NAME ^

Class::DBI::Relationship::IsA - A Class::DBI module for 'Is A' relationships

DESCRIPTION ^

Class::DBI::Relationship::IsA Provides an Is A relationship between Class::DBI classes/tables.

By using this module you can emulate some features of inheritance both within your database and classes through the Class::DBI API.

NOTE: This module is still experimental, several very nasty bugs have been found (and fixed) others may still be lurking - see CAVEATS AND BUGS below.

Warning Will Robinson!

SYNOPSIS ^

In your database (assuming mysql):

 create table person (
   personid int primary key auto_increment,
   firstname varchar(32),
   initials varchar(16),
   surname varchar(64),
   date_of_birth datetime
 );

 create table artist (
   artistid int primary key auto_increment,
   alias varchar(128),
   person int
 );

In your classes:

 package Music::DBI;
 use base 'Class::DBI';

 Music::DBI->connection('dbi:mysql:dbname', 'username', 'password');
 __PACKAGE__->add_relationship_type(is_a => 'Class::DBI::Relationship::IsA');

Superclass:

 package Music::Person;
 use base 'Music::DBI';

 Music::Person->table('person');
 Music::Person->columns(All => qw/personid firstname initials surname date_of_birth/);
 Music::Person->columns(Primary => qw/personid/); # Good practice, less likely to break IsA

Child class:

 package Music::Artist;
 use base 'Music::DBI';
 use Music::Person; # required for access to Music::Person methods

 Music::Artist->table('artist');
 Music::Artist->columns(All => qw/artistid alias/);
 Music::Person->columns(Primary => qw/personid/); # Good practice, less likely to break IsA
 Music::Artist->has_many(cds => 'Music::CD');
 Music::Artist->is_a(person => 'Person'); # Music::Artist inherits accessors from Music::Person

... elsewhere ...

 use Music::Artist;
 my $artist = Music::Artist->create( {firstname=>'Sarah', surname=>'Geller', alias=>'Buffy'});
 $artist->initials('M');
 $artist->update();

BUGS AND CAVEATS ^

* Multiple inheritance is not supported, this is unlikely to change for the forseable future

* is_a must be called after all other cdbi relationship methods otherwise inherited methods and accessors may be over-ridden or clash unexpectedly

* non Class::DBI attributes and methods are not inherited via this module

* The update method is called on the inherited object when the inhertiting object has update called

* Always specify the primary key using columns(Primary => qw/../) if you don't bad things could happen, think of the movies 'Tremors', 'Poltergeist' and 'Evil Dead' all rolled into one but without any heros.

* Very Bad Things can and may occur when using this module even if you use good practice and are cautious -- this includes but is not limited to infinite loops, memory leaks and data corruption.

DEPENDANCIES ^

Class::DBI::AbstractSearch

SEE ALSO ^

perl

Class::DBI

Class::DBI::Relationship

AUTHOR ^

Richard Hundt, <richard@webtk.org.uk>

MAINTAINER ^

Aaron Trevena <aaron.trevena@droogs.org>

COPYRIGHT ^

Licensed for use, modification and distribution under the Artistic and GNU GPL licenses.

Copyright (C) 2004 by Richard Hundt and Aaron Trevena

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.1 or, at your option, any later version of Perl 5 you may have available.

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