DBIx::Class beginners

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 quot;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.quot; - 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 quot;Tables should not be plural as gives you plurals for Result:: package names which represent a single rowquot; - 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} . quot;nquot;; }

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: retrieve DBIx::Class - Lots of ways to do the same thing... quot;There is more than one way to do it (TIMTOWTDI, usually pronounced quot;Tim Toadyquot;) is a Perl mottoquot;

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() . quot;nquot;; }

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(quot;authorsquot;); LPW::DBIC::Result::Authors->add_columns( quot;idquot;, { data_type => quot;INTquot;, default_value => undef, is_nullable => 0, size => 8 }, quot;titlequot;, { data_type => quot;VARCHARquot;, default_value => undef, is_nullable => 1, size => 255, }, ); LPW::DBIC::Result::Authors->set_primary_key(quot;idquot;);

Schema::Loader LPW::DBIC::Result::Books->table(quot;booksquot;); LPW::DBIC::Result::Books->add_columns( quot;idquot;, { data_type => quot;INTquot;, default_value => undef, is_nullable => 0, size => 8 }, quot;namequot;, { data_type => quot;VARCHARquot;, default_value => undef, is_nullable => 1, size => 255, }, quot;authorquot;, { data_type => quot;INTquot;, default_value => undef, is_nullable => 1, size => 8 }, ); LPW::DBIC::Result::Books->set_primary_key(quot;idquot;);

Schema::Loader LPW::DBIC::Result::Authors->has_many(quot;booksquot;, quot;LPW::DBIC::Booksquot;, { quot;foreign.authorquot; => quot;self.idquot; }); LPW::DBIC::Result::Books->belongs_to(quot;authorquot;, quot;LPW::DBIC::Authorsquot;, { id => quot;authorquot; });

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:: 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:: (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:: 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( quot;author_and_booksquot;, quot;LPW::DBIC::Result::AuthorAndBooksquot;, { quot;foreign.bookquot; => quot;self.idquot; }, ); # This is auto generated by Schema::Loader

has_many package LPW::DBIC::Result::Books; __PACKAGE__->has_many( quot;author_and_booksquot;, # Name of accessor quot;LPW::DBIC::Result::AuthorAndBooksquot;, # Related class { quot;foreign.bookquot; => quot;self.idquot; }, # 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( quot;bookquot;, quot;LPW::DBIC::Result::Booksquot;, { id => quot;bookquot; } ); # This is auto generated by Schema::Loader

belongs_to package LPW::DBIC::Result::AuthorAndBooks; __PACKAGE__->belongs_to( quot;bookquot;, # Accessor name quot;LPW::DBIC::Result::Booksquot;, # Related class { id => quot;bookquot; } # 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( quot;authorsquot; => quot;author_and_booksquot;, '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( quot;authorsquot; # Accessor Name => quot;author_and_booksquot;, # 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( quot;booksquot; # Accessor Name => quot;author_and_booksquot;, # 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 quot;many_to_manyquot; via package quot;LPW::DBIC::Result::Authorquot; 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/

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http://www.kt.rim.or.jp	5
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DBIx::Class beginners

by leo lapworth on Nov 29, 2008

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DBIx::Class beginners — Presentation Transcript