3 DBIx::Class::Manual::Cookbook - Miscellaneous recipes
11 When you expect a large number of results, you can ask L<DBIx::Class> for a
12 paged resultset, which will fetch only a defined number of records at a time:
14 my $rs = $schema->resultset('Artist')->search(
17 page => 1, # page to return (defaults to 1)
18 rows => 10, # number of results per page
22 return $rs->all(); # all records for page 1
24 The C<page> attribute does not have to be specified in your search:
26 my $rs = $schema->resultset('Artist')->search(
33 return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records
35 In either of the above cases, you can get a L<Data::Page> object for the
36 resultset (suitable for use in e.g. a template) using the C<pager> method:
40 =head3 Complex WHERE clauses
42 Sometimes you need to formulate a query using specific operators:
44 my @albums = $schema->resultset('Album')->search({
45 artist => { 'like', '%Lamb%' },
46 title => { 'like', '%Fear of Fours%' },
49 This results in something like the following C<WHERE> clause:
51 WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
53 Other queries might require slightly more complex logic:
55 my @albums = $schema->resultset('Album')->search({
58 artist => { 'like', '%Smashing Pumpkins%' },
59 title => 'Siamese Dream',
61 artist => 'Starchildren',
65 This results in the following C<WHERE> clause:
67 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
68 OR artist = 'Starchildren'
70 For more information on generating complex queries, see
71 L<SQL::Abstract/WHERE CLAUSES>.
73 =head3 Arbitrary SQL through a custom ResultSource
75 Sometimes you have to run arbitrary SQL because your query is too complex
76 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
77 be optimized for your database in a special way, but you still want to
78 get the results as a L<DBIx::Class::ResultSet>.
79 The recommended way to accomplish this is by defining a separate ResultSource
80 for your query. You can then inject complete SQL statements using a scalar
81 reference (this is a feature of L<SQL::Abstract>).
83 Say you want to run a complex custom query on your user data, here's what
84 you have to add to your User class:
86 package My::Schema::User;
88 use base qw/DBIx::Class/;
90 # ->load_components, ->table, ->add_columns, etc.
92 # Make a new ResultSource based on the User class
93 my $source = __PACKAGE__->result_source_instance();
94 my $new_source = $source->new( $source );
95 $new_source->source_name( 'UserFriendsComplex' );
97 # Hand in your query as a scalar reference
98 # It will be added as a sub-select after FROM,
99 # so pay attention to the surrounding brackets!
100 $new_source->name( \<<SQL );
101 ( SELECT u.* FROM user u
102 INNER JOIN user_friends f ON u.id = f.user_id
103 WHERE f.friend_user_id = ?
105 SELECT u.* FROM user u
106 INNER JOIN user_friends f ON u.id = f.friend_user_id
107 WHERE f.user_id = ? )
110 # Finally, register your new ResultSource with your Schema
111 My::Schema->register_source( 'UserFriendsComplex' => $new_source );
113 Next, you can execute your complex query using bind parameters like this:
115 my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {},
117 bind => [ 12345, 12345 ]
121 ... and you'll get back a perfect L<DBIx::Class::ResultSet>.
123 =head3 Using specific columns
125 When you only want specific columns from a table, you can use
126 C<columns> to specify which ones you need. This is useful to avoid
127 loading columns with large amounts of data that you aren't about to
130 my $rs = $schema->resultset('Artist')->search(
133 columns => [qw/ name /]
138 # SELECT artist.name FROM artist
140 This is a shortcut for C<select> and C<as>, see below. C<columns>
141 cannot be used together with C<select> and C<as>.
143 =head3 Using database functions or stored procedures
145 The combination of C<select> and C<as> can be used to return the result of a
146 database function or stored procedure as a column value. You use C<select> to
147 specify the source for your column value (e.g. a column name, function, or
148 stored procedure name). You then use C<as> to set the column name you will use
149 to access the returned value:
151 my $rs = $schema->resultset('Artist')->search(
154 select => [ 'name', { LENGTH => 'name' } ],
155 as => [qw/ name name_length /],
160 # SELECT name name, LENGTH( name )
163 Note that the C< as > attribute has absolutely nothing to with the sql
164 syntax C< SELECT foo AS bar > (see the documentation in
165 L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
166 column in your base class (i.e. it was added with C<add_columns>), you
167 just access it as normal. Our C<Artist> class has a C<name> column, so
168 we just use the C<name> accessor:
170 my $artist = $rs->first();
171 my $name = $artist->name();
173 If on the other hand the alias does not correspond to an existing column, you
174 have to fetch the value using the C<get_column> accessor:
176 my $name_length = $artist->get_column('name_length');
178 If you don't like using C<get_column>, you can always create an accessor for
179 any of your aliases using either of these:
181 # Define accessor manually:
182 sub name_length { shift->get_column('name_length'); }
184 # Or use DBIx::Class::AccessorGroup:
185 __PACKAGE__->mk_group_accessors('column' => 'name_length');
187 =head3 SELECT DISTINCT with multiple columns
189 my $rs = $schema->resultset('Foo')->search(
193 { distinct => [ $source->columns ] }
195 as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
199 my $count = $rs->next->get_column('count');
201 =head3 SELECT COUNT(DISTINCT colname)
203 my $rs = $schema->resultset('Foo')->search(
207 { count => { distinct => 'colname' } }
213 =head3 Grouping results
215 L<DBIx::Class> supports C<GROUP BY> as follows:
217 my $rs = $schema->resultset('Artist')->search(
221 select => [ 'name', { count => 'cds.cdid' } ],
222 as => [qw/ name cd_count /],
223 group_by => [qw/ name /]
228 # SELECT name, COUNT( cds.cdid ) FROM artist me
229 # LEFT JOIN cd cds ON ( cds.artist = me.artistid )
232 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
233 are in any way unsure about the use of the attributes above (C< join
234 >, C< select >, C< as > and C< group_by >).
236 =head3 Predefined searches
238 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
239 and define often used searches as methods:
241 package My::DBIC::ResultSet::CD;
244 use base 'DBIx::Class::ResultSet';
246 sub search_cds_ordered {
249 return $self->search(
251 { order_by => 'name DESC' },
257 To use your resultset, first tell DBIx::Class to create an instance of it
258 for you, in your My::DBIC::Schema::CD class:
260 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
262 Then call your new method in your code:
264 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
266 =head3 Using SQL functions on the left hand side of a comparison
268 Using SQL functions on the left hand side of a comparison is generally
269 not a good idea since it requires a scan of the entire table. However,
270 it can be accomplished with C<DBIx::Class> when necessary.
272 If you do not have quoting on, simply include the function in your search
273 specification as you would any column:
275 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
277 With quoting on, or for a more portable solution, use the C<where>
280 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
284 (When the bind args ordering bug is fixed, this technique will be better
285 and can replace the one above.)
287 With quoting on, or for a more portable solution, use the C<where> and
291 where => \'YEAR(date_of_birth) = ?',
297 =head2 Using joins and prefetch
299 You can use the C<join> attribute to allow searching on, or sorting your
300 results by, one or more columns in a related table. To return all CDs matching
301 a particular artist name:
303 my $rs = $schema->resultset('CD')->search(
305 'artist.name' => 'Bob Marley'
308 join => [qw/artist/], # join the artist table
313 # SELECT cd.* FROM cd
314 # JOIN artist ON cd.artist = artist.id
315 # WHERE artist.name = 'Bob Marley'
317 If required, you can now sort on any column in the related tables by including
318 it in your C<order_by> attribute:
320 my $rs = $schema->resultset('CD')->search(
322 'artist.name' => 'Bob Marley'
325 join => [qw/ artist /],
326 order_by => [qw/ artist.name /]
331 # SELECT cd.* FROM cd
332 # JOIN artist ON cd.artist = artist.id
333 # WHERE artist.name = 'Bob Marley'
334 # ORDER BY artist.name
336 Note that the C<join> attribute should only be used when you need to search or
337 sort using columns in a related table. Joining related tables when you only
338 need columns from the main table will make performance worse!
340 Now let's say you want to display a list of CDs, each with the name of the
341 artist. The following will work fine:
343 while (my $cd = $rs->next) {
344 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
347 There is a problem however. We have searched both the C<cd> and C<artist> tables
348 in our main query, but we have only returned data from the C<cd> table. To get
349 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
352 SELECT artist.* FROM artist WHERE artist.id = ?
354 A statement like the one above will run for each and every CD returned by our
355 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
358 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
359 This allows you to fetch results from related tables in advance:
361 my $rs = $schema->resultset('CD')->search(
363 'artist.name' => 'Bob Marley'
366 join => [qw/ artist /],
367 order_by => [qw/ artist.name /],
368 prefetch => [qw/ artist /] # return artist data too!
372 # Equivalent SQL (note SELECT from both "cd" and "artist"):
373 # SELECT cd.*, artist.* FROM cd
374 # JOIN artist ON cd.artist = artist.id
375 # WHERE artist.name = 'Bob Marley'
376 # ORDER BY artist.name
378 The code to print the CD list remains the same:
380 while (my $cd = $rs->next) {
381 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
384 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
385 so no additional SQL statements are executed. You now have a much more
388 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
389 C<has_many> relationships.
391 Also note that C<prefetch> should only be used when you know you will
392 definitely use data from a related table. Pre-fetching related tables when you
393 only need columns from the main table will make performance worse!
395 =head3 Multi-step joins
397 Sometimes you want to join more than one relationship deep. In this example,
398 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
399 contain a specific string:
401 # Relationships defined elsewhere:
402 # Artist->has_many('cds' => 'CD', 'artist');
403 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
405 my $rs = $schema->resultset('Artist')->search(
407 'liner_notes.notes' => { 'like', '%some text%' },
411 'cds' => 'liner_notes'
417 # SELECT artist.* FROM artist
418 # JOIN ( cd ON artist.id = cd.artist )
419 # JOIN ( liner_notes ON cd.id = liner_notes.cd )
420 # WHERE liner_notes.notes LIKE '%some text%'
422 Joins can be nested to an arbitrary level. So if we decide later that we
423 want to reduce the number of Artists returned based on who wrote the liner
426 # Relationship defined elsewhere:
427 # LinerNotes->belongs_to('author' => 'Person');
429 my $rs = $schema->resultset('Artist')->search(
431 'liner_notes.notes' => { 'like', '%some text%' },
432 'author.name' => 'A. Writer'
437 'liner_notes' => 'author'
444 # SELECT artist.* FROM artist
445 # JOIN ( cd ON artist.id = cd.artist )
446 # JOIN ( liner_notes ON cd.id = liner_notes.cd )
447 # JOIN ( author ON author.id = liner_notes.author )
448 # WHERE liner_notes.notes LIKE '%some text%'
449 # AND author.name = 'A. Writer'
451 =head2 Multi-step prefetch
453 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
454 deep using the same syntax as a multi-step join:
456 my $rs = $schema->resultset('Tag')->search(
466 # SELECT tag.*, cd.*, artist.* FROM tag
467 # JOIN cd ON tag.cd = cd.cdid
468 # JOIN artist ON cd.artist = artist.artistid
470 Now accessing our C<cd> and C<artist> relationships does not need additional
473 my $tag = $rs->first;
474 print $tag->cd->artist->name;
476 =head2 Columns of data
478 If you want to find the sum of a particular column there are several
479 ways, the obvious one is to use search:
481 my $rs = $schema->resultset('Items')->search(
484 select => [ { sum => 'Cost' } ],
485 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
488 my $tc = $rs->first->get_column('total_cost');
490 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
491 returned when you ask the C<ResultSet> for a column using
494 my $cost = $schema->resultset('Items')->get_column('Cost');
497 With this you can also do:
499 my $minvalue = $cost->min;
500 my $maxvalue = $cost->max;
502 Or just iterate through the values of this column only:
504 while ( my $c = $cost->next ) {
508 foreach my $c ($cost->all) {
512 C<ResultSetColumn> only has a limited number of built-in functions, if
513 you need one that it doesn't have, then you can use the C<func> method
516 my $avg = $cost->func('AVERAGE');
518 This will cause the following SQL statement to be run:
520 SELECT AVERAGE(Cost) FROM Items me
522 Which will of course only work if your database supports this function.
523 See L<DBIx::Class::ResultSetColumn> for more documentation.
525 =head2 Using relationships
527 =head3 Create a new row in a related table
529 my $book->create_related('author', { name => 'Fred'});
531 =head3 Search in a related table
533 Only searches for books named 'Titanic' by the author in $author.
535 my $author->search_related('books', { name => 'Titanic' });
537 =head3 Delete data in a related table
539 Deletes only the book named Titanic by the author in $author.
541 my $author->delete_related('books', { name => 'Titanic' });
543 =head3 Ordering a relationship result set
545 If you always want a relation to be ordered, you can specify this when you
546 create the relationship.
548 To order C<< $book->pages >> by descending page_number.
550 Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
556 As of version 0.04001, there is improved transaction support in
557 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
558 example of the recommended way to use it:
560 my $genus = $schema->resultset('Genus')->find(12);
568 $genus->add_to_species({ name => 'troglodyte' });
571 $schema->txn_do($coderef2); # Can have a nested transaction
572 return $genus->species;
577 $rs = $schema->txn_do($coderef1);
580 if ($@) { # Transaction failed
581 die "the sky is falling!" #
582 if ($@ =~ /Rollback failed/); # Rollback failed
584 deal_with_failed_transaction();
587 Nested transactions will work as expected. That is, only the outermost
588 transaction will actually issue a commit to the $dbh, and a rollback
589 at any level of any transaction will cause the entire nested
590 transaction to fail. Support for savepoints and for true nested
591 transactions (for databases that support them) will hopefully be added
594 =head2 Many-to-many relationships
596 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
599 # ... set up connection ...
603 __PACKAGE__->table('user');
604 __PACKAGE__->add_columns(qw/id name/);
605 __PACKAGE__->set_primary_key('id');
606 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
607 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
609 package My::UserAddress;
611 __PACKAGE__->table('user_address');
612 __PACKAGE__->add_columns(qw/user address/);
613 __PACKAGE__->set_primary_key(qw/user address/);
614 __PACKAGE__->belongs_to('user' => 'My::User');
615 __PACKAGE__->belongs_to('address' => 'My::Address');
619 __PACKAGE__->table('address');
620 __PACKAGE__->add_columns(qw/id street town area_code country/);
621 __PACKAGE__->set_primary_key('id');
622 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
623 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
625 $rs = $user->addresses(); # get all addresses for a user
626 $rs = $address->users(); # get all users for an address
628 =head2 Setting default values for a row
630 It's as simple as overriding the C<new> method. Note the use of
634 my ( $class, $attrs ) = @_;
636 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
638 my $new = $class->next::method($attrs);
643 For more information about C<next::method>, look in the L<Class::C3>
644 documentation. See also L<DBIx::Class::Manual::Component> for more
645 ways to write your own base classes to do this.
647 People looking for ways to do "triggers" with DBIx::Class are probably
648 just looking for this.
650 =head2 Stringification
652 Employ the standard stringification technique by using the C<overload>
655 To make an object stringify itself as a single column, use something
656 like this (replace C<foo> with the column/method of your choice):
658 use overload '""' => sub { shift->name}, fallback => 1;
660 For more complex stringification, you can use an anonymous subroutine:
662 use overload '""' => sub { $_[0]->name . ", " .
663 $_[0]->address }, fallback => 1;
665 =head3 Stringification Example
667 Suppose we have two tables: C<Product> and C<Category>. The table
670 Product(id, Description, category)
671 Category(id, Description)
673 C<category> is a foreign key into the Category table.
675 If you have a Product object C<$obj> and write something like
679 things will not work as expected.
681 To obtain, for example, the category description, you should add this
682 method to the class defining the Category table:
684 use overload "" => sub {
687 return $self->Description;
690 =head2 Disconnecting cleanly
692 If you find yourself quitting an app with Control-C a lot during
693 development, you might like to put the following signal handler in
694 your main database class to make sure it disconnects cleanly:
697 __PACKAGE__->storage->disconnect;
700 =head2 Schema import/export
702 To create a DBIx::Class schema from an existing database, use
703 L<DBIx::Class::Schema::Loader>'s C<make_schema_at>:
705 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
707 The following functionality requires you to have L<SQL::Translator>
708 (also known as "SQL Fairy") installed.
710 To create a set of database-specific .sql files for the above schema:
712 my $schema = My::Schema->connect($dsn);
713 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
718 By default this will create schema files in the current directory, for
719 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
721 To create a new database using the schema:
723 my $schema = My::Schema->connect($dsn);
724 $schema->deploy({ add_drop_tables => 1});
726 To import created .sql files using the mysql client:
728 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
730 To create C<ALTER TABLE> conversion scripts to update a database to a
731 newer version of your schema at a later point, first set a new
732 $VERSION in your Schema file, then:
734 my $schema = My::Schema->connect($dsn);
735 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
741 This will produce new database-specific .sql files for the new version
742 of the schema, plus scripts to convert from version 0.1 to 0.2. This
743 requires that the files for 0.1 as created above are available in the
744 given directory to diff against.
747 =head2 Easy migration from class-based to schema-based setup
749 You want to start using the schema-based approach to L<DBIx::Class>
750 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
751 of existing classes that you don't want to move by hand. Try this nifty script
757 my $schema = MyDB->schema_instance;
759 my $translator = SQL::Translator->new(
760 debug => $debug || 0,
761 trace => $trace || 0,
762 no_comments => $no_comments || 0,
763 show_warnings => $show_warnings || 0,
764 add_drop_table => $add_drop_table || 0,
765 validate => $validate || 0,
767 'DBIx::Schema' => $schema,
770 'prefix' => 'My::Schema',
774 $translator->parser('SQL::Translator::Parser::DBIx::Class');
775 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
777 my $output = $translator->translate(@args) or die
778 "Error: " . $translator->error;
782 You could use L<Module::Find> to search for all subclasses in the MyDB::*
783 namespace, which is currently left as an exercise for the reader.
785 =head2 Schema versioning
787 The following example shows simplistically how you might use DBIx::Class to
788 deploy versioned schemas to your customers. The basic process is as follows:
794 Create a DBIx::Class schema
806 Modify schema to change functionality
810 Deploy update to customers
814 =head3 Create a DBIx::Class schema
816 This can either be done manually, or generated from an existing database as
817 described under C<Schema import/export>.
819 =head3 Save the schema
821 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L<Schema
824 =head3 Deploy to customers
826 There are several ways you could deploy your schema. These are probably
827 beyond the scope of this recipe, but might include:
833 Require customer to apply manually using their RDBMS.
837 Package along with your app, making database dump/schema update/tests
838 all part of your install.
842 =head3 Modify the schema to change functionality
844 As your application evolves, it may be necessary to modify your schema
845 to change functionality. Once the changes are made to your schema in
846 DBIx::Class, export the modified schema and the conversion scripts as
847 in L<Schema import/export>.
849 =head3 Deploy update to customers
851 Add the L<DBIx::Class::Schema::Versioned> schema component to your
852 Schema class. This will add a new table to your database called
853 C<SchemaVersions> which will keep track of which version is installed
854 and warn if the user trys to run a newer schema version than the
855 database thinks it has.
857 Alternatively, you can send the conversion sql scripts to your
860 =head2 Setting limit dialect for SQL::Abstract::Limit
862 In some cases, SQL::Abstract::Limit cannot determine the dialect of
863 the remote SQL server by looking at the database handle. This is a
864 common problem when using the DBD::JDBC, since the DBD-driver only
865 know that in has a Java-driver available, not which JDBC driver the
866 Java component has loaded. This specifically sets the limit_dialect
867 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
870 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
872 The JDBC bridge is one way of getting access to a MSSQL server from a platform
873 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
875 =head2 Setting quoting for the generated SQL.
877 If the database contains column names with spaces and/or reserved words, they
878 need to be quoted in the SQL queries. This is done using:
880 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
881 __PACKAGE__->storage->sql_maker->name_sep('.');
883 The first sets the quote characters. Either a pair of matching
884 brackets, or a C<"> or C<'>:
886 __PACKAGE__->storage->sql_maker->quote_char('"');
888 Check the documentation of your database for the correct quote
889 characters to use. C<name_sep> needs to be set to allow the SQL
890 generator to put the quotes the correct place.
892 =head2 Overloading methods
894 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
895 method calls, useful for things like default values and triggers. You have to
896 use calls to C<next::method> to overload methods. More information on using
897 L<Class::C3> with L<DBIx::Class> can be found in
898 L<DBIx::Class::Manual::Component>.
900 =head3 Changing one field whenever another changes
902 For example, say that you have three columns, C<id>, C<number>, and
903 C<squared>. You would like to make changes to C<number> and have
904 C<squared> be automagically set to the value of C<number> squared.
905 You can accomplish this by overriding C<store_column>:
908 my ( $self, $name, $value ) = @_;
909 if ($name eq 'number') {
910 $self->squared($value * $value);
912 $self->next::method($name, $value);
915 Note that the hard work is done by the call to C<next::method>, which
916 redispatches your call to store_column in the superclass(es).
918 =head3 Automatically creating related objects
920 You might have a class C<Artist> which has many C<CD>s. Further, if you
921 want to create a C<CD> object every time you insert an C<Artist> object.
922 You can accomplish this by overriding C<insert> on your objects:
925 my ( $self, @args ) = @_;
926 $self->next::method(@args);
927 $self->cds->new({})->fill_from_artist($self)->insert;
931 where C<fill_from_artist> is a method you specify in C<CD> which sets
932 values in C<CD> based on the data in the C<Artist> object you pass in.
934 =head2 Debugging DBIx::Class objects with Data::Dumper
936 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
937 be hard to find the pertinent data in all the data it can generate.
938 Specifically, if one naively tries to use it like so,
942 my $cd = $schema->resultset('CD')->find(1);
945 several pages worth of data from the CD object's schema and result source will
946 be dumped to the screen. Since usually one is only interested in a few column
947 values of the object, this is not very helpful.
949 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
950 it. Simply define a hook that L<Data::Dumper> will call on the object before
951 dumping it. For example,
958 result_source => undef,
966 local $Data::Dumper::Freezer = '_dumper_hook';
968 my $cd = $schema->resultset('CD')->find(1);
970 # dumps $cd without its ResultSource
972 If the structure of your schema is such that there is a common base class for
973 all your table classes, simply put a method similar to C<_dumper_hook> in the
974 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
975 will automagically clean up your data before printing it. See
976 L<Data::Dumper/EXAMPLES> for more information.
978 =head2 Retrieving a row object's Schema
980 It is possible to get a Schema object from a row object like so:
982 my $schema = $cd->result_source->schema;
983 # use the schema as normal:
984 my $artist_rs = $schema->resultset('Artist');
986 This can be useful when you don't want to pass around a Schema object to every
991 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
992 executed as well as notifications of query completion and transaction
993 begin/commit. If you'd like to profile the SQL you can subclass the
994 L<DBIx::Class::Storage::Statistics> class and write your own profiling
997 package My::Profiler;
1000 use base 'DBIx::Class::Storage::Statistics';
1002 use Time::HiRes qw(time);
1011 $self->print("Executing $sql: ".join(', ', @params)."\n");
1020 my $elapsed = sprintf("%0.4f", time() - $start);
1021 $self->print("Execution took $elapsed seconds.\n");
1027 You can then install that class as the debugging object:
1029 __PACKAGE__->storage->debugobj(new My::Profiler());
1030 __PACKAGE__->storage->debug(1);
1032 A more complicated example might involve storing each execution of SQL in an
1040 my $elapsed = time() - $start;
1041 push(@{ $calls{$sql} }, {
1047 You could then create average, high and low execution times for an SQL
1048 statement and dig down to see if certain parameters cause aberrant behavior.
1049 You might want to check out L<DBIx::Class::QueryLog> as well.
1051 =head2 Getting the value of the primary key for the last database insert
1053 AKA getting last_insert_id
1055 If you are using PK::Auto, this is straightforward:
1057 my $foo = $rs->create(\%blah);
1059 my $id = $foo->id; # foo->my_primary_key_field will also work.
1061 If you are not using autoincrementing primary keys, this will probably
1062 not work, but then you already know the value of the last primary key anyway.
1064 =head2 Dynamic Sub-classing DBIx::Class proxy classes
1065 (AKA multi-class object inflation from one table)
1067 L<DBIx::Class> classes are proxy classes, therefore some different
1068 techniques need to be employed for more than basic subclassing. In
1069 this example we have a single user table that carries a boolean bit
1070 for admin. We would like like to give the admin users
1071 objects(L<DBIx::Class::Row>) the same methods as a regular user but
1072 also special admin only methods. It doesn't make sense to create two
1073 seperate proxy-class files for this. We would be copying all the user
1074 methods into the Admin class. There is a cleaner way to accomplish
1077 Overriding the C<inflate_result> method within the User proxy-class
1078 gives us the effect we want. This method is called by
1079 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
1080 grab the object being returned, inspect the values we are looking for,
1081 bless it if it's an admin object, and then return it. See the example
1084 B<Schema Definition>
1088 use base qw/DBIx::Class::Schema/;
1090 __PACKAGE__->load_classes(qw/User/);
1093 B<Proxy-Class definitions>
1095 package DB::Schema::User;
1099 use base qw/DBIx::Class/;
1101 ### Defined what our admin class is for ensure_class_loaded
1102 my $admin_class = __PACKAGE__ . '::Admin';
1104 __PACKAGE__->load_components(qw/Core/);
1106 __PACKAGE__->table('users');
1108 __PACKAGE__->add_columns(qw/user_id email password
1109 firstname lastname active
1112 __PACKAGE__->set_primary_key('user_id');
1114 sub inflate_result {
1116 my $ret = $self->next::method(@_);
1117 if( $ret->admin ) {### If this is an admin rebless for extra functions
1118 $self->ensure_class_loaded( $admin_class );
1119 bless $ret, $admin_class;
1125 print "I am a regular user.\n";
1130 package DB::Schema::User::Admin;
1134 use base qw/DB::Schema::User/;
1138 print "I am an admin.\n";
1144 print "I am doing admin stuff\n";
1148 B<Test File> test.pl
1154 my $user_data = { email => 'someguy@place.com',
1155 password => 'pass1',
1158 my $admin_data = { email => 'someadmin@adminplace.com',
1159 password => 'pass2',
1162 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
1164 $schema->resultset('User')->create( $user_data );
1165 $schema->resultset('User')->create( $admin_data );
1167 ### Now we search for them
1168 my $user = $schema->resultset('User')->single( $user_data );
1169 my $admin = $schema->resultset('User')->single( $admin_data );
1171 print ref $user, "\n";
1172 print ref $admin, "\n";
1174 print $user->password , "\n"; # pass1
1175 print $admin->password , "\n";# pass2; inherited from User
1176 print $user->hello , "\n";# I am a regular user.
1177 print $admin->hello, "\n";# I am an admin.
1179 ### The statement below will NOT print
1180 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
1181 ### The statement below will print
1182 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
1184 =head2 Skip object creation for faster results
1186 DBIx::Class is not built for speed, it's built for convenience and
1187 ease of use, but sometimes you just need to get the data, and skip the
1190 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
1192 my $rs = $schema->resultset('CD');
1194 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1196 my $hash_ref = $rs->find(1);
1200 =head2 Get raw data for blindingly fast results
1202 If the C<inflate_result> solution above is not fast enough for you, you
1203 can use a DBIx::Class to return values exactly as they come out of the
1204 data base with none of the convenience methods wrapped round them.
1206 This is used like so:-
1208 my $cursor = $rs->cursor
1209 while (my @vals = $cursor->next) {
1210 # use $val[0..n] here
1213 You will need to map the array offsets to particular columns (you can
1214 use the I<select> attribute of C<search()> to force ordering).
1216 =head2 Want to know if find_or_create found or created a row?
1218 Just use C<find_or_new> instead, then check C<in_storage>:
1220 my $obj = $rs->find_or_new({ blah => 'blarg' });
1221 unless ($obj->in_storage) {
1223 # do whatever else you wanted if it was a new row
1226 =head3 Wrapping/overloading a column accessor
1228 Problem: Say you have a table "Camera" and want to associate a description
1229 with each camera. For most cameras, you'll be able to generate the description from
1230 the other columns. However, in a few special cases you may want to associate a
1231 custom description with a camera.
1235 In your database schema, define a description field in the "Camera" table that
1236 can contain text and null values.
1238 In DBIC, we'll overload the column accessor to provide a sane default if no
1239 custom description is defined. The accessor will either return or generate the
1240 description, depending on whether the field is null or not.
1242 First, in your "Camera" schema class, define the description field as follows:
1244 __PACKAGE__->add_columns(description => { accessor => '_description' });
1246 Next, we'll define the accessor-wrapper subroutine:
1251 # If there is an update to the column, we'll let the original accessor
1253 return $self->_description(@_) if @_;
1255 # Fetch the column value.
1256 my $description = $self->_description;
1258 # If there's something in the description field, then just return that.
1259 return $description if defined $description && length $descripton;
1261 # Otherwise, generate a description.
1262 return $self->generate_description;