Compose and access new related objects without inserting

Question

Without using database I would like to construct a new DBIx::Class object (song) and attach a few multi-to-multi related objects (tag) to it. Then I would like to access tags in this way:

my @tags = $song->tags();

I already can do this if I first insert objects into database, but how to do this without using insert()?

Below is my code which outputs name of created tag. Now I would like to achieve this without using insert.

This is just test code. Otherwise I have a more complex schema that is used with MySql. Now I also use Solr and I want to convert Solr response to DBIx::Class objects (without accessing db).

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

package MySchema::Song;
use base 'DBIx::Class';
__PACKAGE__->load_components('Core');
__PACKAGE__->table("artist");
__PACKAGE__->add_columns(
    id   => { data_type => 'integer', is_nullable => 0, is_auto_increment => 1 },
    name => { data_type => 'varchar', is_nullable => 1, },
);
__PACKAGE__->set_primary_key('id');
__PACKAGE__->has_many('song_tag' => 'MySchema::SongTag', 'song_id');
__PACKAGE__->many_to_many('tags' => 'song_tag', 'tag');

package MySchema::Tag;
use base 'DBIx::Class';
__PACKAGE__->load_components('Core');
__PACKAGE__->table("tag");
__PACKAGE__->add_columns(
    id   => { data_type => 'integer', is_nullable => 0, is_auto_increment => 1 },
    name => { data_type => 'varchar', is_nullable => 1, },
);
__PACKAGE__->set_primary_key('id');
__PACKAGE__->has_many('song_tag' => 'MySchema::SongTag', 'tag_id');
__PACKAGE__->many_to_many('songs' => 'song_tag', 'song');

package MySchema::SongTag;
use base 'DBIx::Class';
__PACKAGE__->load_components('Core');
__PACKAGE__->table("song_tag");
__PACKAGE__->add_columns(
    song_id => { data_type => 'integer', is_nullable => 0 },
    tag_id  => { data_type => 'integer', is_nullable => 0 },
);
__PACKAGE__->set_primary_key( qw(song_id tag_id) );
__PACKAGE__->belongs_to('song' => 'MySchema::Song','song_id');
__PACKAGE__->belongs_to('tag' => 'MySchema::Tag', 'tag_id');


package MySchema;
use base 'DBIx::Class::Schema';
__PACKAGE__->load_classes(qw(Song Tag SongTag));


package main;

my $schema;
$schema = MySchema->connect('dbi:SQLite:dbname=:memory:');
$schema->deploy;

my $song = $schema->resultset('Song')->new_result({ id => 1, name => 'Song name' });
my $tag = $schema->resultset('Tag')->new_result({ id => 1, name => 'Tag name' });

my $song_tag = $schema->resultset('SongTag')->new({
    song => $song,
    tag => $tag,
});

$song->add_to_tags($tag);
#$tag->add_to_songs($song); # one or another

$song->insert;
$tag->insert;

# This works if objects are previously inserted
foreach my $tag ($song->tags) {
    print $tag->name."\n";
}

1;

Answer 1

I found a solution which is not so nice, but it works without accessing db. To achieve this SongTag and Tag objects needs to be cached inside Song object, otherwise $song->tags() will access db.

package main;

my $schema;
$schema = MySchema->connect('dbi:SQLite:dbname=:memory:');
$schema->deploy;

$schema->storage->debug(1);

my $song = $schema->resultset('Song')->new_result({ id => 1, name => 'Song name' });
my $tag = $schema->resultset('Tag')->new_result({ id => 98, name => 'Tag name' });
my $tag2 = $schema->resultset('Tag')->new_result({ id => 99, name => 'Tag name 2' });

# create many-to-many relations in memory without accessing database

my $rel = $schema->resultset('SongTag')->search(); # cretes empty resultset object

$rel->{related_resultsets}->{tag} = $schema->resultset('Tag')->search();
$rel->{related_resultsets}->{tag}->set_cache([ $tag, $tag2 ]);

$song->{related_resultsets}->{song_tag} = $schema->resultset('SongTag')->search();
$song->{related_resultsets}->{song_tag}->set_cache([ $rel ]);

foreach my $tag ($song->tags) {
    print $tag->name."\n";
}

1;