Demystifying DBIx::Class

Demystifying DBIx::Class Jay Shirley <jshirley@coldhardcode.com> http://our.coldhardcode.com/svn/DBIC-Beer

Mystic?

Why are ORMs scary?

Why are ORMs scary? • Enterprise-y

Why are ORMs scary? • Enterprise-y • Loss of control

Why are ORMs scary? • Enterprise-y • Loss of control • History (Class::DBI)

Why are ORMs scary? • Enterprise-y • Loss of control • History (Class::DBI) • (A triumph of multiple inheritance)

Retort.

Enterprise-y

Enterprise-y • Enterprise = Java

Enterprise-y • Enterprise = Java • DBIx::Class is written in perl

Loss of Control

Loss of Control • Still programmatic

Loss of Control • Still programmatic • Use SQL::Abstract rather than SQL

Loss of Control • Still programmatic • Use SQL::Abstract rather than SQL • Same thing

Loss of Control • Still programmatic • Use SQL::Abstract rather than SQL • Same thing • (except patches welcome)

Class::DBI

Class::DBI Sorry Schwern

Why DBIx::Class? • I like it. You’ll see why. • TIMTOWDI: • Rose::DB • Alzabo

Objects • Relations are only a third of an ORM

Objects • Relations are only a third of an ORM • What’s an object?

Objects • Relations are only a third of an ORM • What’s an object? • Database columns

Objects • Relations are only a third of an ORM • What’s an object? • Database columns • Table

Objects • Relations are only a third of an ORM • What’s an object? • Database columns • Table • Indexes

A Use Case

Yes, Beer.

Or... • Beer has many distributers • Beer has many reviews • Beer belongs to a brewer

Which means... package Beer::Schema::Beer; use base 'DBIx::Class'; __PACKAGE__->load_components( qw|Core| ); __PACKAGE__->table('beer'); __PACKAGE__->add_columns( 'pk1' => { data_type => 'integer', size => 16, is_nullable => 0, is_auto_increment => 1 }, 'name' => { data_type => 'varchar', size => 128, is_nullable => 0 }, 'brewer_pk1' => { data_type => 'integer', size => 16, is_nullable => 0, is_foreign_key => 1 }, ); __PACKAGE__->set_primary_key('pk1'); 1;

And indexes: __PACKAGE__->add_unique_index(...);

That gives you: • Deployable SQL (CREATE TABLE, etc) • The foundation for relationships: • $beer->brewer # DTRT

Managing Relations • A beer is: • made by a brewer • distributed by distributers • reviewed by people

Simple Relationships belongs_to is the opposite end of has_many

Simple Relationships belongs_to is the opposite end of has_many has_one, might_have means just that

Simple Relationships belongs_to is the opposite end of has_many has_one, might_have means just that many_to_many gets complicated

Creating a relation __PACKAGE__->belongs_to( ‘brewer’, # Accessor ‘Beer::Schema::Brewer’, # Related Class ‘brewer_pk1’ # My Column );

For simplicity... Brewers, Distributors and Beers are all easy All the same, except Beer has a brewer (brewer_pk1)

Using it (Manager) use Beer::Schema; my $schema = Beer::Schema ->connect( $dsn );

$schema # Fetch a result set my $rs = $schema->resultset(‘Beer’);

Result Sets # Everything is a result set. $rs->count; # How many Beers?

Everything is a Result Set $rs2 = $rs->search({ name => ‘Stout’ }); $rs2->count; # It chains together.

Chained Result Sets are what make DBIC Great

Result Sets return Result Sets $rs->search->search->search- >search->search->search ->search- >search->search->search->search- >search ->search->search->search- >search->search->search ->search- >search->search->search->search- >search ->search->search->search- >search->search->search ->search- >search->search->search->search- >search;

Why? $rs ->search({ $long_query }) ->search({ $more_filters }) ->search({ $even_more });

Actual Use: sub active_members { # All profiles that have purchased a membership. my $query = $rs->search( { 'purchase.saved_object_key' => 'membership', 'membership.expiration_date' => '>= NOW()' }, { join => { profile_transactions => { 'transaction' => { 'link_transaction_purchase' => { 'purchase' => 'membership' } } }, }, prefetch => [ 'state', 'country', { profile_transactions => { 'transaction' => { 'link_transaction_purchase' => { 'purchase' => 'membership' } } }, } ], group_by => [ qw/membership_id/ ] } ); }

In SQL: SELECT ... FROM table_profiles me LEFT JOIN profile_transaction profile_transactions ON ( profile_transactions.profile_id = me.profile_id ) JOIN nasa_transactions transaction ON ( transaction.transaction_id = profile_transactions.transaction_id ) LEFT JOIN link_trans_pp link_transaction_purchase ON ( link_transaction_purchase.transaction_id = transaction.transaction_id ) JOIN purchased_products purchase ON ( purchase.purchased_id = link_transaction_purchase.purchased_id ) JOIN nasa_membership membership ON ( membership.membership_id = purchase.saved_product_id ) JOIN state_lookup state ON ( state.state_lookup_id = me.state ) JOIN country_lookup country ON ( country.country_lookup_id = me.country_id ) WHERE ( membership.expiration_date >= NOW() AND purchase.saved_object_key = 'membership' )

Now: my $query = $schema->resultset(‘Profile’)->active_members; $query->count; # How many? $query->search({ first_name => ‘Bob’ }); # All matching members named Bob $query->search({ first_name => ‘Bob’ })->count; while ( my $profile = $query->next ) { $profile->cars; # Get all of this persons cars } # Clean, no ugly SQL

Pretty.

Even More: Managing your schema

Create Table Statements $schema->create_ddl_dir( [ 'SQLite', 'MySQL', ‘PostgreSQL’ ], $VERSION, quot;$destinationquot; );

SQLite CREATE TABLE beer ( pk1 INTEGER PRIMARY KEY NOT NULL, name varchar(128) NOT NULL, brewer_pk1 integer(16) NOT NULL );

DROP TABLE IF EXISTS `beer`; MySQL -- -- Table: `beer` -- CREATE TABLE `beer` ( `pk1` integer(16) NOT NULL auto_increment, `name` varchar(128) NOT NULL, `brewer_pk1` integer(16) NOT NULL, INDEX (`pk1`), INDEX (`brewer_pk1`), PRIMARY KEY (`pk1`), CONSTRAINT `beer_fk_brewer_pk1` FOREIGN KEY (`brewer_pk1`) REFERENCES `brewer` (`pk1`) ON DELETE CASCADE ON UPDATE CASCADE ) Type=InnoDB;

PostgreSQL -- -- Table: beer -- DROP TABLE beer CASCADE; CREATE TABLE beer ( pk1 bigserial NOT NULL, name character varying(128) NOT NULL, brewer_pk1 bigint NOT NULL, PRIMARY KEY (pk1) );

Get a working database $schema->deploy; # Yes, it is this simple.

And now for tests

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Demystifying DBIx::Class

by Jay Shirley on Jun 24, 2008

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Demystifying DBIx::Class — Presentation Transcript