DBIx::Class (aka DBIC)
for (advanced) beginners
Leo Lapworth @ LPW 2008
http://leo.cuckoo.org/projects/

assumptions
You know a little about Perl
and using objects
You know a little bit about
databases and using foreign
keys

DBIx::Class?
• ORM (object relational mapper)
• SQL <-> OO (using objects instead of SQL)
• Simple, powerful, complex, fab and confusing
• There are many ORMs, DBIx::Class just happens to
be the best in Perl (personal opinion)

why this talk?
• Help avoid mistakes I made!
• Help learn DBIx::Class faster
• Make your coding easier

point of note
\"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it.\" - Brian W. Kernighan
This talk is about making it easy so we you are less
likely to get confused

table setup

example...
Books
Authors

authors table
CREATE TABLE authors(
id int(8) primary key auto_increment,
name varchar(255)
) engine = InnoDB DEFAULT CHARSET=utf8;

tips
Name tables as simple plurals (add an S) -
makes relationships easier to understand
(issue: Matt Trout \"Tables should not be plural as gives you plurals for Result::
package names which represent a single row\" - talk may be rewritten in future
to reflect this as this is better once you understand the relationship setup -
either way, consistency is important)
Use a character set (UTF8) from the start
(for international characters)

authors table
CREATE TABLE author s(
id int(8) primary key auto_increment,
name varchar(255)
) engine = InnoDB DEFAULT CHARSET= utf8;

books table
CREATE TABLE books(
id int(8) primary key auto_increment,
title varchar(255),
author int(8),
foreign key (author)
references authors(id)
) engine = InnoDB DEFAULT CHARSET=utf8;

tips
Name link fields as singular
Check foreign key is the same field type and
size in both tables

books table
CREATE TABLE books(
id int(8) primary key auto_increment,
title varchar(255),
author int(8),
foreign key ( author)
references authors(id)
) engine = InnoDB DEFAULT CHARSET=utf8;

CRUD compared
C - Create
R - Retrieve
U - Update
D - Delete

Manual (SQL)

manual: create
my $sth = $dbh->prepare('
INSERT INTO books
(title, author)
values (?,?)
');
$sth->execute(
'A book title',$author_id
);

manual: create
my $sth = $dbh->prepare('
INSERT INTO books
(title, author)
values (?,?)
');
$sth->execute(
'A book title', $author_id
);

manual: retrieve
my $sth = $dbh->prepare('
SELECT title,
authors.name as author_name
FROM books, authors
WHERE books.author = authors.id
');

manual: retrieve
while( my $book = $sth->fetchrow_hashref() )
{
print 'Author of '
. $book->{title}
. ' is '
. $book->{author_name}
. \"\\n\";
}

manual: update
my $update = $dbh->prepare('
UPDATE books
SET title = ?
WHERE id = ?
');
$update->execute(
'New title', $book_id);

manual: delete
my $delete = $dbh->prepare('
DELETE FROM books
WHERE id = ?
');
$delete->execute( $book_id);

DBIx::Class

DBIC: create
my $book = $book_model->create({
title => 'A book title',
author => $author_id,
});
Look ma, no SQL!
Tip: do not pass in primary_key field, even if its empty/undef as the
object returned will have an empty id, even if your field is auto
increment.

DBIC: create
my $book = $book_model->create({
title => 'A book title',
author => $author_id,
});

DBIC: create
my $pratchett = $author_model->create({
name => 'Terry Pratchett',
});

DBIC: create
my $book = $pratchett->create_related(
'books', {
title => 'Another Discworld book',
});
or
my $book = $pratchett->add_to_books({
title => 'Another Discworld book',
});

DBIC: create
my $book = $pratchett->create_related(
'books', {
title => 'Another Discworld book',
});
or
my $book = $pratchett->add_to_books({
title => 'Another Discworld book',
});

DBIC: retrieve
DBIx::Class - Lots of ways to do the same thing...
\"There is more than one way to do it (TIMTOWTDI,
usually pronounced \"Tim Toady\") is a Perl motto\"

DBIC: retrieve
my $book = $book_model->find($book_id);
my $book = $book_model->search({
title => 'A book title',
})->single();
my @books = $book_model->search({
author => $author_id,
})->all();

DBIC: retrieve
while( my $book = $books_rs->next() ) {
print 'Author of '
. $book->title()
. ' is '
. $book->author()->name()
. \"\\n\";
}

DBIC: retrieve
my $books_rs = $book_model->search({
author => $author_id,
});
Search takes SQL::Abstract formatted queries
> perldoc SQL::Abstract

DBIC: update
$book->update({
title => 'New title',
});

DBIC: delete
$book->delete();

Creating models

too much
typing!
too much
maintenance!

Schema::Loader
Tip
LPW::DBIC::Result::XX
LPW::DBIC::ResultSet::XX

splitting logic
cleanly
LPW::DBIC::Result::XXX = an individual row
LPW::DBIC::ResultSet::XXX = searches / results

using your Schema

DEBUGGING
DBIC_TRACE=1 ./your_script.pl

Schema::Loader
LPW::DBIC::Result::Authors->table(\"authors\");
LPW::DBIC::Result::Authors->add_columns(
\"id\",
{ data_type => \"INT\", default_value => undef,
is_nullable => 0, size => 8 },
\"title\",
{
data_type => \"VARCHAR\",
default_value => undef,
is_nullable => 1,
size => 255,
},
);
LPW::DBIC::Result::Authors->set_primary_key(\"id\");

Schema::Loader
LPW::DBIC::Result::Books->table(\"books\");
LPW::DBIC::Result::Books->add_columns(
\"id\",
{ data_type => \"INT\", default_value => undef,
is_nullable => 0, size => 8 },
\"name\",
{
data_type => \"VARCHAR\",
default_value => undef,
is_nullable => 1,
size => 255,
},
\"author\",
{ data_type => \"INT\", default_value => undef,
is_nullable => 1, size => 8 },
);
LPW::DBIC::Result::Books->set_primary_key(\"id\");

Schema::Loader
LPW::DBIC::Result::Authors->has_many(\"books\", \"LPW::DBIC::Books\",
{ \"foreign.author\" => \"self.id\" });
LPW::DBIC::Result::Books->belongs_to(\"author\",
\"LPW::DBIC::Authors\", { id => \"author\" });

Schema::Loader

SQL - debugging
INSERT INTO authors (name)
VALUES (?): 'Douglas Adams'
INSERT INTO books (author, title)
VALUES (?, ?): '5', '42'

overloading
LPW::DBIC::Result::Books
LPW:: DBIC::ResultSet::Books
LPW:: DBIC::Result::Authors
LPW:: DBIC::ResultSet::Authors

Result::
package LPW::DBIC::Result::Books;
use base 'DBIx::Class';
use strict;
use warnings;
sub isbn {
my $self = shift;
# search amazon or something
my $api = Amazon::API->book({
title => $self->title()
});
return $api->isbn();
}
1;

Result::
package LPW::DBIC::Result::Books;
use base 'DBIx::Class';
use strict;
use warnings;
sub isbn {
my $self = shift;
# search amazon or something
my $api = Amazon::API->book({
title => $self->title()
});
return $api->isbn();
}
1;

Result::
print $book->isbn();

Result:: (inflating)
package LPW::DBIC::Result::Books;
use base 'DBIx::Class';
use strict;
use warnings;
use DateTime::Format::MySQL;
__PACKAGE__->inflate_column(
'date_published',
{ inflate => sub {
DateTime::Format::MySQL->parse_date(shift);
},
deflate => sub {
shift->ymd();
},
}
);
# Automatic see: DBIx::Class::InflateColumn::DateTime

Result:: (inflating)
package LPW::DBIC::Result::Books;
use base 'DBIx::Class';
use strict;
use warnings;
use DateTime::Format::MySQL;
__PACKAGE__->inflate_column(
'date_published',
{ inflate => sub {
DateTime::Format::MySQL->parse_date(shift);
},
deflate => sub {
shift->ymd();
},
}
);
# Automatic see: DBIx::Class::InflateColumn::DateTime

Result:: (deflating)
$book->date_published(DateTime->now);
$book->update();
2008-11-29

Result:: (inflating)
my $date_published = $book->date_published()
print $date_published->month_abbr();
Nov

ResultSets::
package LPW::DBIC::ResultSet::Books;
use base 'DBIx::Class::ResultSet';
sub the_ultimate_books {
my $self = shift;
return $self->search(
{ title => {
'like', '%42%'
}
});
}
sub by_author {
my ( $self, $author ) = @_;
return $self->search( { author => $author->id(), } );
}
1;

ResultSets::
package LPW::DBIC::ResultSet::Books;
use base 'DBIx::Class::ResultSet';
sub the_ultimate_books {
my $self = shift;
return $self->search(
{ title => {
'like', '%42%'
}
});
}
sub by_author {
my ( $self, $author ) = @_;
return $self->search( { author => $author->id(), } );
}

ResultSets::
package LPW::DBIC::ResultSet::Books;
use base 'DBIx::Class::ResultSet';
sub the_ultimate_books {
my $self = shift;
return $self->search(
{ title => {
'like', '%42%'
}
});
}
sub by_author {
my ( $self, $author ) = @_;
return $self->search( {
author => $author->id(),
} );
}

ResultSets::
use LPW::DBIC;
my $book_model = LPW::DBIC->resultset('Books');
my $book_rs = $book_model->the_ultimate_books();
my @books = $book_rs->all();

ResultSets::chaining
use LPW::DBIC;
my $book_model = LPW::DBIC->resultset('Books');
my $author_model = LPW::DBIC->resultset('Authors');
my $author = $author_model->search({
name => 'Douglas Adams',
})->single();
my $book_rs = $book_model->the_ultimate_books()
->by_author($author);
my @books = $book_rs->all();

ResultSets::chaining
my $book_rs = $book_model
->the_ultimate_books()
->by_author($author);
or
my $book_rs = $book_model
->the_ultimate_books();
$book_rs = $book_rs->by_author($author);
# Debug (SQL):
# SELECT me.id, me.title, me.date_published, me.author
# FROM books me
# WHERE ( ( ( author = ? ) AND ( title LIKE ? ) ) ): '5', '%42%'

ResultSets::chaining
my $rs = $book_model
->category('childrens')
->by_author($author)
->published_after('1812')
->first_page_contains('once upon')
->rating_greater_than(4);
my @books = $rs->all();

overloading before
new record

overloading before
new record
package LPW::DBIC::Result::Authors;
use base 'DBIx::Class';
sub new {
my ( $class, $attrs ) = @_;
# Mess with $attrs
my $new = $class->next::method($attrs);
return $new;
}
1;

relationships

multiple authors

a few relationships
has_many has_many
Authors Authors_and_Books Books
belongs_to belongs_to
many_to_many

a few relationships
!

new join table
CREATE TABLE author_and_books(
id int(8) primary key auto_increment,
book
int(8),
author int(8),
foreign key (book) references books(id),
foreign key (author) references authors(id)
) engine = InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE `books` DROP `author`

new join table
CREATE TABLE author_and_books(
id int(8) primary key auto_increment,
book
int(8),
author int(8),
foreign key (book) references books(id),
foreign key (author) references authors(id)
) engine = InnoDB DEFAULT CHARSET=utf8;

has_many
has_many
Books Authors_and_Books
belongs_to

has_many
package LPW::DBIC::Result::Books;
__PACKAGE__->has_many(
\"author_and_books\",
\"LPW::DBIC::Result::AuthorAndBooks\",
{ \"foreign.book\" => \"self.id\" },
);
# This is auto generated by Schema::Loader

has_many
package LPW::DBIC::Result::Books;
__PACKAGE__->has_many(
\"author_and_books\",
# Name of accessor
\"LPW::DBIC::Result::AuthorAndBooks\",
# Related class
{ \"foreign.book\" => \"self.id\" },
# Relationship (magic often works if not
# specified, but avoid!)
);

belongs_to
has_many
Books Authors_and_Books
belongs_to

belongs_to
package LPW::DBIC::Result::AuthorAndBooks;
__PACKAGE__->belongs_to(
\"book\",
\"LPW::DBIC::Result::Books\",
{ id => \"book\" }
);
# This is auto generated by Schema::Loader

belongs_to
package LPW::DBIC::Result::AuthorAndBooks;
__PACKAGE__->belongs_to(
\"book\", # Accessor name
\"LPW::DBIC::Result::Books\", # Related class
{ id => \"book\" } # Relationship
);

same for Authors
has_many
Authors Authors_and_Books
belongs_to

with no coding...
has_many has_many
Authors Authors_and_Books Books
belongs_to belongs_to

many_to_many
has_many has_many
Authors Authors_and_Books Books
belongs_to belongs_to
many_to_many

many_to_many
package LPW::DBIC::Result::Books;
use base 'DBIx::Class';
__PACKAGE__->many_to_many(
\"authors\"
=> \"author_and_books\",
'author'
);
1;
# This is NOT auto generated by Schema::Loader

many_to_many
package LPW::DBIC::Result::Books;
use base 'DBIx::Class';
__PACKAGE__->many_to_many(
\"authors\"
# Accessor Name
=> \"author_and_books\",
# has_many accessor_name
'author'
# foreign relationship name
);
1;

many_to_many
package LPW::DBIC::Result::Authors;
use base 'DBIx::Class';
__PACKAGE__->many_to_many(
\"books\"
# Accessor Name
=> \"author_and_books\",
# has_many accessor_name
'book'
# foreign relationship name
);
1;
# This is NOT auto generated by Schema::Loader

using many_to_many
#!/usr/bin/perl
use LPW::DBIC;
my $author_model = LPW::DBIC->resultset('Authors');
my $author = $author_model->search({
name => 'Douglas Adams',
})->single();
$author->add_to_books({
title => 'A new book',
});

using many_to_many
my $author = $author_model->search({
name => 'Douglas Adams',
})->single();
$author->add_to_books({
title => 'A new book',
});
# SELECT me.id, me.name FROM authors me
# WHERE ( name = ? ): 'Douglas Adams';
# INSERT INTO books (title) VALUES (?): 'A new book';
# INSERT INTO author_and_books (author, book)
# VALUES (?, ?): '5', '2';

using many_to_many
$author->add_to_books($book);
$book->add_to_authors($author_1);
$book->add_to_authors($author_2);

in 16 lines of code
has_many has_many
Authors Authors_and_Books Books
belongs_to belongs_to
many_to_many

errors
Read them closely!

error messages
DBIx::Class::Schema::Loader::connection
(): Failed to load external class
definition for
'LPW::DBIC::Result::Authors': Can't
locate object method \"many_to_many\" via
package \"LPW::DBIC::Result::Author\" at
lib/LPW/DBIC/Result/Authors.pm line 9.
Compilation failed in require at /
Library/Perl/5.8.8/DBIx/Class/Schema/
Loader/Base.pm line 292.

error messages
DBIx::Class::Schema::Loader::connection
(): Failed to load external class
definition for
'LPW::DBIC::Result::Authors': Can't
locate object method \"many_to_many\" via
package \"LPW::DBIC::Result::Author\" at
lib/LPW/DBIC/Result/Authors.pm line 9.
Compilation failed in require at /
Library/Perl/5.8.8/DBIx/Class/Schema/
Loader/Base.pm line 292.

errors
• Turn on debugging
• Read error messages (sometimes useful!)
• Check field names
• Check package names
• Check which database you are connected
to (development/test/live?) - repeat above

thanks
http://leo.cuckoo.org/projects/
Time for bonus slides?

Template Toolkit
• [% author.books.count %] not working?
• TT all methods are called in list context
• [% author.books_rs.count %] scalar context
Available for all relationships

Catalyst
package Your::App::Model::LPW;
use base qw(Catalyst::Model::DBIC::Schema);
use strict;
use warnings;
__PACKAGE__->config(
schema_class => 'LPW::DBIC',
);
1;

Catalyst
package Your::App::Model::LPW;
use base qw(Catalyst::Model::DBIC::Schema);
use strict;
use warnings;
__PACKAGE__->config(
schema_class => 'LPW::DBIC',
);
1;
Keep your Scheme in a separate
package to your Catalyst application

Catalyst
sub action_name : Local {
my ($self, $c) = @_;
my $model = $c->model('DBIC::LPW');
my $author_model = $model->resultset('Authors');
}
1;

thanks!
http://leo.cuckoo.org/projects/