Describir la Aplicación

Class::DBI trabaja con un modelo una clase/una tabla. Las tablas de la base de datos deben estar previamente definidas e iniciadas.

Para describir la base de datos de manera que los objetos puedan ser construidos porClass::DBI se requieren varios pasos.

Establecer una Clase Base

Es conveniente establecer una clase base de la cual hereden las clases asociadas con las diferentes tablas. La introducción de esta clase proporciona un lugar conveniente para las sobreescrituras y extensiones que queramos hacer a Class::DBI.

$ cat -n synopsis1.pl
 1  package Music::DBI;
 2  use strict;
 3
 4  use base 'Class::DBI';
 5  Music::DBI->connection("dbi:SQLite:example.db");

Lo primero es conocer como acceder a la base de datos. Esto se hace por medio del método connection. Esto hace que todas las clases/tabla que heredan de la clase base compartan la misma conexión.

Establecer cada Clase y Declarar las Columnas

 7  package Music::Artist;
 8  use base 'Music::DBI';
 9  Music::Artist->table('artist');
10  Music::Artist->columns(All => qw/artistid name/);
11  Music::Artist->has_many(cds => 'Music::CD');
12
13  package Music::CD;
14  use base 'Music::DBI';
15  Music::CD->table('cd');
16  Music::CD->columns(All => qw/cdid artist title/);
17  Music::CD->has_many(tracks => 'Music::Track');
18  Music::CD->has_a(artist => 'Music::Artist');
19
20  package Music::Track;
21  use base 'Music::DBI';
22  Music::Track->table('track');
23  Music::Track->columns(All => qw/trackid cd title/);
24
25  my $artist = Music::Artist->insert({ name => 'U2' });
26
27  my $cd = $artist->add_to_cds({
28    title  => 'October',
29  });
30
31  $cd->update;

Ejecución:

lhp@nereida:~/Lperl/src/CLASS_DBI$ perl synopsis1.pl
lhp@nereida:~/Lperl/src/CLASS_DBI$ sqlite3 example.db
SQLite version 3.3.8
Enter ".help" for instructions
sqlite> .dump
BEGIN TRANSACTION;
CREATE TABLE artist (
  artistid INTEGER PRIMARY KEY,
  name TEXT NOT NULL
);
INSERT INTO "artist" VALUES(1, 'Michael Jackson');
INSERT INTO "artist" VALUES(2, 'Eminem');
INSERT INTO "artist" VALUES(3, 'U2');
CREATE TABLE cd (
  cdid INTEGER PRIMARY KEY,
  artist INTEGER NOT NULL REFERENCES artist(artistid),
  title TEXT NOT NULL
);
INSERT INTO "cd" VALUES(1, 1, 'Thriller');
INSERT INTO "cd" VALUES(2, 1, 'Bad');
INSERT INTO "cd" VALUES(3, 2, 'The Marshall Mathers LP');
INSERT INTO "cd" VALUES(4, 3, 'October');
CREATE TABLE track (
  trackid INTEGER PRIMARY KEY,
  cd INTEGER NOT NULL REFERENCES cd(cdid),
  title TEXT NOT NULL
);
INSERT INTO "track" VALUES(1, 3, 'The Way I Am');
INSERT INTO "track" VALUES(2, 3, 'Stan');
INSERT INTO "track" VALUES(3, 1, 'Billie Jean');
INSERT INTO "track" VALUES(4, 2, 'Leave Me Alone');
INSERT INTO "track" VALUES(5, 2, 'Smooth Criminal');
INSERT INTO "track" VALUES(6, 1, 'Beat It');
INSERT INTO "track" VALUES(7, 2, 'Dirty Diana');
COMMIT;
sqlite>

lhp@nereida:~/Lperl/src/CLASS_DBI$ cat -n synopsis2.pl
 1  #!/usr/local/bin/perl -w
..  .............................. # like in the former example
25
26  my $cd = Music::Artist->search_like(name => 'Eminem')->first;
27
28  print $cd->artistid,": ",$cd->name,"\n";
29
30  my $first = Music::Artist->retrieve(1);
31  print $first->name,"\n";
32
33  print "CDs\n";
34  for my $cd (Music::CD->retrieve_all) {
35    print "\t",$cd->title,"\n";
36  }

lhp@nereida:~/Lperl/src/CLASS_DBI$ perl synopsis2.pl
2: Eminem
Michael Jackson
CDs
        Thriller
        Bad
        The Marshall Mathers LP