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 small 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 return 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 =head2 Using joins and prefetch
268 You can use the C<join> attribute to allow searching on, or sorting your
269 results by, one or more columns in a related table. To return all CDs matching
270 a particular artist name:
272 my $rs = $schema->resultset('CD')->search(
274 'artist.name' => 'Bob Marley'
277 join => [qw/artist/], # join the artist table
282 # SELECT cd.* FROM cd
283 # JOIN artist ON cd.artist = artist.id
284 # WHERE artist.name = 'Bob Marley'
286 If required, you can now sort on any column in the related tables by including
287 it in your C<order_by> attribute:
289 my $rs = $schema->resultset('CD')->search(
291 'artist.name' => 'Bob Marley'
294 join => [qw/ artist /],
295 order_by => [qw/ artist.name /]
300 # SELECT cd.* FROM cd
301 # JOIN artist ON cd.artist = artist.id
302 # WHERE artist.name = 'Bob Marley'
303 # ORDER BY artist.name
305 Note that the C<join> attribute should only be used when you need to search or
306 sort using columns in a related table. Joining related tables when you only
307 need columns from the main table will make performance worse!
309 Now let's say you want to display a list of CDs, each with the name of the
310 artist. The following will work fine:
312 while (my $cd = $rs->next) {
313 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
316 There is a problem however. We have searched both the C<cd> and C<artist> tables
317 in our main query, but we have only returned data from the C<cd> table. To get
318 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
321 SELECT artist.* FROM artist WHERE artist.id = ?
323 A statement like the one above will run for each and every CD returned by our
324 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
327 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
328 This allows you to fetch results from related tables in advance:
330 my $rs = $schema->resultset('CD')->search(
332 'artist.name' => 'Bob Marley'
335 join => [qw/ artist /],
336 order_by => [qw/ artist.name /],
337 prefetch => [qw/ artist /] # return artist data too!
341 # Equivalent SQL (note SELECT from both "cd" and "artist"):
342 # SELECT cd.*, artist.* FROM cd
343 # JOIN artist ON cd.artist = artist.id
344 # WHERE artist.name = 'Bob Marley'
345 # ORDER BY artist.name
347 The code to print the CD list remains the same:
349 while (my $cd = $rs->next) {
350 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
353 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
354 so no additional SQL statements are executed. You now have a much more
357 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
358 C<has_many> relationships.
360 Also note that C<prefetch> should only be used when you know you will
361 definitely use data from a related table. Pre-fetching related tables when you
362 only need columns from the main table will make performance worse!
364 =head3 Multi-step joins
366 Sometimes you want to join more than one relationship deep. In this example,
367 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
368 contain a specific string:
370 # Relationships defined elsewhere:
371 # Artist->has_many('cds' => 'CD', 'artist');
372 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
374 my $rs = $schema->resultset('Artist')->search(
376 'liner_notes.notes' => { 'like', '%some text%' },
380 'cds' => 'liner_notes'
386 # SELECT artist.* FROM artist
387 # JOIN ( cd ON artist.id = cd.artist )
388 # JOIN ( liner_notes ON cd.id = liner_notes.cd )
389 # WHERE liner_notes.notes LIKE '%some text%'
391 Joins can be nested to an arbitrary level. So if we decide later that we
392 want to reduce the number of Artists returned based on who wrote the liner
395 # Relationship defined elsewhere:
396 # LinerNotes->belongs_to('author' => 'Person');
398 my $rs = $schema->resultset('Artist')->search(
400 'liner_notes.notes' => { 'like', '%some text%' },
401 'author.name' => 'A. Writer'
406 'liner_notes' => 'author'
413 # SELECT artist.* FROM artist
414 # JOIN ( cd ON artist.id = cd.artist )
415 # JOIN ( liner_notes ON cd.id = liner_notes.cd )
416 # JOIN ( author ON author.id = liner_notes.author )
417 # WHERE liner_notes.notes LIKE '%some text%'
418 # AND author.name = 'A. Writer'
420 =head2 Multi-step prefetch
422 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
423 deep using the same syntax as a multi-step join:
425 my $rs = $schema->resultset('Tag')->search(
435 # SELECT tag.*, cd.*, artist.* FROM tag
436 # JOIN cd ON tag.cd = cd.cdid
437 # JOIN artist ON cd.artist = artist.artistid
439 Now accessing our C<cd> and C<artist> relationships does not need additional
442 my $tag = $rs->first;
443 print $tag->cd->artist->name;
445 =head2 Columns of data
447 If you want to find the sum of a particular column there are several
448 ways, the obvious one is to use search:
450 my $rs = $schema->resultset('Items')->search(
453 select => [ { sum => 'Cost' } ],
454 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
457 my $tc = $rs->first->get_column('total_cost');
459 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
460 returned when you ask the C<ResultSet> for a column using
463 my $cost = $schema->resultset('Items')->get_column('Cost');
466 With this you can also do:
468 my $minvalue = $cost->min;
469 my $maxvalue = $cost->max;
471 Or just iterate through the values of this column only:
473 while ( my $c = $cost->next ) {
477 foreach my $c ($cost->all) {
481 C<ResultSetColumn> only has a limited number of built-in functions, if
482 you need one that it doesn't have, then you can use the C<func> method
485 my $avg = $cost->func('AVERAGE');
487 This will cause the following SQL statement to be run:
489 SELECT AVERAGE(Cost) FROM Items me
491 Which will of course only work if your database supports this function.
492 See L<DBIx::Class::ResultSetColumn> for more documentation.
494 =head2 Using relationships
496 =head3 Create a new row in a related table
498 my $book->create_related('author', { name => 'Fred'});
500 =head3 Search in a related table
502 Only searches for books named 'Titanic' by the author in $author.
504 my $author->search_related('books', { name => 'Titanic' });
506 =head3 Delete data in a related table
508 Deletes only the book named Titanic by the author in $author.
510 my $author->delete_related('books', { name => 'Titanic' });
512 =head3 Ordering a relationship result set
514 If you always want a relation to be ordered, you can specify this when you
515 create the relationship.
517 To order C<< $book->pages >> by descending page_number.
519 Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
525 As of version 0.04001, there is improved transaction support in
526 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
527 example of the recommended way to use it:
529 my $genus = $schema->resultset('Genus')->find(12);
537 $genus->add_to_species({ name => 'troglodyte' });
540 $schema->txn_do($coderef2); # Can have a nested transaction
541 return $genus->species;
546 $rs = $schema->txn_do($coderef1);
549 if ($@) { # Transaction failed
550 die "the sky is falling!" #
551 if ($@ =~ /Rollback failed/); # Rollback failed
553 deal_with_failed_transaction();
556 Nested transactions will work as expected. That is, only the outermost
557 transaction will actually issue a commit to the $dbh, and a rollback
558 at any level of any transaction will cause the entire nested
559 transaction to fail. Support for savepoints and for true nested
560 transactions (for databases that support them) will hopefully be added
563 =head2 Many-to-many relationships
565 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
568 # ... set up connection ...
572 __PACKAGE__->table('user');
573 __PACKAGE__->add_columns(qw/id name/);
574 __PACKAGE__->set_primary_key('id');
575 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
576 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
578 package My::UserAddress;
580 __PACKAGE__->table('user_address');
581 __PACKAGE__->add_columns(qw/user address/);
582 __PACKAGE__->set_primary_key(qw/user address/);
583 __PACKAGE__->belongs_to('user' => 'My::User');
584 __PACKAGE__->belongs_to('address' => 'My::Address');
588 __PACKAGE__->table('address');
589 __PACKAGE__->add_columns(qw/id street town area_code country/);
590 __PACKAGE__->set_primary_key('id');
591 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
592 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
594 $rs = $user->addresses(); # get all addresses for a user
595 $rs = $address->users(); # get all users for an address
597 =head2 Setting default values for a row
599 It's as simple as overriding the C<new> method. Note the use of
603 my ( $class, $attrs ) = @_;
605 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
607 my $new = $class->next::method($attrs);
612 For more information about C<next::method>, look in the L<Class::C3>
613 documentation. See also L<DBIx::Class::Manual::Component> for more
614 ways to write your own base classes to do this.
616 People looking for ways to do "triggers" with DBIx::Class are probably
617 just looking for this.
619 =head2 Stringification
621 Employ the standard stringification technique by using the C<overload>
624 To make an object stringify itself as a single column, use something
625 like this (replace C<foo> with the column/method of your choice):
627 use overload '""' => sub { shift->name}, fallback => 1;
629 For more complex stringification, you can use an anonymous subroutine:
631 use overload '""' => sub { $_[0]->name . ", " .
632 $_[0]->address }, fallback => 1;
634 =head3 Stringification Example
636 Suppose we have two tables: C<Product> and C<Category>. The table
639 Product(id, Description, category)
640 Category(id, Description)
642 C<category> is a foreign key into the Category table.
644 If you have a Product object C<$obj> and write something like
648 things will not work as expected.
650 To obtain, for example, the category description, you should add this
651 method to the class defining the Category table:
653 use overload "" => sub {
656 return $self->Description;
659 =head2 Disconnecting cleanly
661 If you find yourself quitting an app with Control-C a lot during
662 development, you might like to put the following signal handler in
663 your main database class to make sure it disconnects cleanly:
666 __PACKAGE__->storage->disconnect;
669 =head2 Schema import/export
671 This functionality requires you to have L<SQL::Translator> (also known as
672 "SQL Fairy") installed.
674 To create a DBIx::Class schema from an existing database:
677 --to DBIx::Class::File
678 --prefix "MySchema" > MySchema.pm
680 To create a MySQL database from an existing L<DBIx::Class> schema, convert the
681 schema to MySQL's dialect of SQL:
683 sqlt --from SQL::Translator::Parser::DBIx::Class
685 --DBIx::Class "MySchema.pm" > Schema1.sql
687 And import using the mysql client:
689 mysql -h "host" -D "database" -u "user" -p < Schema1.sql
691 =head2 Easy migration from class-based to schema-based setup
693 You want to start using the schema-based approach to L<DBIx::Class>
694 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
695 of existing classes that you don't want to move by hand. Try this nifty script
701 my $schema = MyDB->schema_instance;
703 my $translator = SQL::Translator->new(
704 debug => $debug || 0,
705 trace => $trace || 0,
706 no_comments => $no_comments || 0,
707 show_warnings => $show_warnings || 0,
708 add_drop_table => $add_drop_table || 0,
709 validate => $validate || 0,
711 'DBIx::Schema' => $schema,
714 'prefix' => 'My::Schema',
718 $translator->parser('SQL::Translator::Parser::DBIx::Class');
719 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
721 my $output = $translator->translate(@args) or die
722 "Error: " . $translator->error;
726 You could use L<Module::Find> to search for all subclasses in the MyDB::*
727 namespace, which is currently left as an exercise for the reader.
729 =head2 Schema versioning
731 The following example shows simplistically how you might use DBIx::Class to
732 deploy versioned schemas to your customers. The basic process is as follows:
738 Create a DBIx::Class schema
750 Modify schema to change functionality
754 Deploy update to customers
758 =head3 Create a DBIx::Class schema
760 This can either be done manually, or generated from an existing database as
761 described under C<Schema import/export>.
763 =head3 Save the schema
765 Use C<sqlt> to transform your schema into an SQL script suitable for your
766 customer's database. E.g. for MySQL:
768 sqlt --from SQL::Translator::Parser::DBIx::Class
770 --DBIx::Class "MySchema.pm" > Schema1.mysql.sql
772 If you need to target databases from multiple vendors, just generate an SQL
773 script suitable for each. To support PostgreSQL too:
775 sqlt --from SQL::Translator::DBIx::Class
777 --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql
779 =head3 Deploy to customers
781 There are several ways you could deploy your schema. These are probably
782 beyond the scope of this recipe, but might include:
788 Require customer to apply manually using their RDBMS.
792 Package along with your app, making database dump/schema update/tests
793 all part of your install.
797 =head3 Modify the schema to change functionality
799 As your application evolves, it may be necessary to modify your schema to
800 change functionality. Once the changes are made to your schema in DBIx::Class,
801 export the modified schema as before, taking care not to overwrite the original:
803 sqlt --from SQL::Translator::DBIx::Class
805 --DBIx::Class "Anything.pm" > Schema2.mysql.sql
807 Next, use sqlt-diff to create an SQL script that will update the customer's
810 sqlt-diff --to MySQL Schema1=MySQL Schema2=MySQL > SchemaUpdate.mysql.sql
812 =head3 Deploy update to customers
814 The schema update can be deployed to customers using the same method as before.
816 =head2 Setting limit dialect for SQL::Abstract::Limit
818 In some cases, SQL::Abstract::Limit cannot determine the dialect of
819 the remote SQL server by looking at the database handle. This is a
820 common problem when using the DBD::JDBC, since the DBD-driver only
821 know that in has a Java-driver available, not which JDBC driver the
822 Java component has loaded. This specifically sets the limit_dialect
823 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
826 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
828 The JDBC bridge is one way of getting access to a MSSQL server from a platform
829 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
831 =head2 Setting quoting for the generated SQL.
833 If the database contains column names with spaces and/or reserved words, they
834 need to be quoted in the SQL queries. This is done using:
836 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
837 __PACKAGE__->storage->sql_maker->name_sep('.');
839 The first sets the quote characters. Either a pair of matching
840 brackets, or a C<"> or C<'>:
842 __PACKAGE__->storage->sql_maker->quote_char('"');
844 Check the documentation of your database for the correct quote
845 characters to use. C<name_sep> needs to be set to allow the SQL
846 generator to put the quotes the correct place.
848 =head2 Overloading methods
850 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
851 method calls, useful for things like default values and triggers. You have to
852 use calls to C<next::method> to overload methods. More information on using
853 L<Class::C3> with L<DBIx::Class> can be found in
854 L<DBIx::Class::Manual::Component>.
856 =head3 Changing one field whenever another changes
858 For example, say that you have three columns, C<id>, C<number>, and
859 C<squared>. You would like to make changes to C<number> and have
860 C<squared> be automagically set to the value of C<number> squared.
861 You can accomplish this by overriding C<store_column>:
864 my ( $self, $name, $value ) = @_;
865 if ($name eq 'number') {
866 $self->squared($value * $value);
868 $self->next::method($name, $value);
871 Note that the hard work is done by the call to C<next::method>, which
872 redispatches your call to store_column in the superclass(es).
874 =head3 Automatically creating related objects
876 You might have a class C<Artist> which has many C<CD>s. Further, if you
877 want to create a C<CD> object every time you insert an C<Artist> object.
878 You can accomplish this by overriding C<insert> on your objects:
881 my ( $self, @args ) = @_;
882 $self->next::method(@args);
883 $self->cds->new({})->fill_from_artist($self)->insert;
887 where C<fill_from_artist> is a method you specify in C<CD> which sets
888 values in C<CD> based on the data in the C<Artist> object you pass in.
890 =head2 Debugging DBIx::Class objects with Data::Dumper
892 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
893 be hard to find the pertinent data in all the data it can generate.
894 Specifically, if one naively tries to use it like so,
898 my $cd = $schema->resultset('CD')->find(1);
901 several pages worth of data from the CD object's schema and result source will
902 be dumped to the screen. Since usually one is only interested in a few column
903 values of the object, this is not very helpful.
905 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
906 it. Simply define a hook that L<Data::Dumper> will call on the object before
907 dumping it. For example,
914 result_source => undef,
922 local $Data::Dumper::Freezer = '_dumper_hook';
924 my $cd = $schema->resultset('CD')->find(1);
926 # dumps $cd without its ResultSource
928 If the structure of your schema is such that there is a common base class for
929 all your table classes, simply put a method similar to C<_dumper_hook> in the
930 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
931 will automagically clean up your data before printing it. See
932 L<Data::Dumper/EXAMPLES> for more information.
934 =head2 Retrieving a row object's Schema
936 It is possible to get a Schema object from a row object like so:
938 my $schema = $cd->result_source->schema;
939 # use the schema as normal:
940 my $artist_rs = $schema->resultset('Artist');
942 This can be useful when you don't want to pass around a Schema object to every
947 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
948 executed as well as notifications of query completion and transaction
949 begin/commit. If you'd like to profile the SQL you can subclass the
950 L<DBIx::Class::Storage::Statistics> class and write your own profiling
953 package My::Profiler;
956 use base 'DBIx::Class::Storage::Statistics';
958 use Time::HiRes qw(time);
967 print "Executing $sql: ".join(', ', @params)."\n";
976 printf("Execution took %0.4f seconds.\n", time() - $start);
982 You can then install that class as the debugging object:
984 __PACKAGE__->storage()->debugobj(new My::Profiler());
985 __PACKAGE__->storage()->debug(1);
987 A more complicated example might involve storing each execution of SQL in an
995 my $elapsed = time() - $start;
996 push(@{ $calls{$sql} }, {
1002 You could then create average, high and low execution times for an SQL
1003 statement and dig down to see if certain parameters cause aberrant behavior.
1005 =head2 Getting the value of the primary key for the last database insert
1007 AKA getting last_insert_id
1009 If you are using PK::Auto, this is straightforward:
1011 my $foo = $rs->create(\%blah);
1013 my $id = $foo->id; # foo->my_primary_key_field will also work.
1015 If you are not using autoincrementing primary keys, this will probably
1016 not work, but then you already know the value of the last primary key anyway.
1018 =head2 Dynamic Sub-classing DBIx::Class proxy classes
1019 (AKA multi-class object inflation from one table)
1021 L<DBIx::Class> classes are proxy classes, therefore some different
1022 techniques need to be employed for more than basic subclassing. In
1023 this example we have a single user table that carries a boolean bit
1024 for admin. We would like like to give the admin users
1025 objects(L<DBIx::Class::Row>) the same methods as a regular user but
1026 also special admin only methods. It doesn't make sense to create two
1027 seperate proxy-class files for this. We would be copying all the user
1028 methods into the Admin class. There is a cleaner way to accomplish
1031 Overriding the C<inflate_result> method within the User proxy-class
1032 gives us the effect we want. This method is called by
1033 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
1034 grab the object being returned, inspect the values we are looking for,
1035 bless it if it's an admin object, and then return it. See the example
1038 B<Schema Definition>
1042 use base qw/DBIx::Class::Schema/;
1044 __PACKAGE__->load_classes(qw/User/);
1047 B<Proxy-Class definitions>
1049 package DB::Schema::User;
1053 use base qw/DBIx::Class/;
1055 ### Defined what our admin class is for ensure_class_loaded
1056 my $admin_class = __PACKAGE__ . '::Admin';
1058 __PACKAGE__->load_components(qw/Core/);
1060 __PACKAGE__->table('users');
1062 __PACKAGE__->add_columns(qw/user_id email password
1063 firstname lastname active
1066 __PACKAGE__->set_primary_key('user_id');
1068 sub inflate_result {
1070 my $ret = $self->next::method(@_);
1071 if( $ret->admin ) {### If this is an admin rebless for extra functions
1072 $self->ensure_class_loaded( $admin_class );
1073 bless $ret, $admin_class;
1079 print "I am a regular user.\n";
1084 package DB::Schema::User::Admin;
1088 use base qw/DB::Schema::User/;
1092 print "I am an admin.\n";
1098 print "I am doing admin stuff\n";
1102 B<Test File> test.pl
1108 my $user_data = { email => 'someguy@place.com',
1109 password => 'pass1',
1112 my $admin_data = { email => 'someadmin@adminplace.com',
1113 password => 'pass2',
1116 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
1118 $schema->resultset('User')->create( $user_data );
1119 $schema->resultset('User')->create( $admin_data );
1121 ### Now we search for them
1122 my $user = $schema->resultset('User')->single( $user_data );
1123 my $admin = $schema->resultset('User')->single( $admin_data );
1125 print ref $user, "\n";
1126 print ref $admin, "\n";
1128 print $user->password , "\n"; # pass1
1129 print $admin->password , "\n";# pass2; inherited from User
1130 print $user->hello , "\n";# I am a regular user.
1131 print $admin->hello, "\n";# I am an admin.
1133 ### The statement below will NOT print
1134 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
1135 ### The statement below will print
1136 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
1138 =head2 Skip object creation for faster results
1140 DBIx::Class is not built for speed, it's built for convenience and
1141 ease of use, but sometimes you just need to get the data, and skip the
1144 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
1146 my $rs = $schema->resultset('CD');
1148 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1150 my $hash_ref = $rs->find(1);
1154 =head2 Get raw data for blindingly fast results
1156 If the C<inflate_result> solution above is not fast enough for you, you
1157 can use a DBIx::Class to return values exactly as they come out of the
1158 data base with none of the convenience methods wrapped round them.
1160 This is used like so:-
1162 my $cursor = $rs->cursor
1163 while (my @vals = $cursor->next) {
1164 # use $val[0..n] here
1167 You will need to map the array offsets to particular columns (you can
1168 use the I<select> attribute of C<search()> to force ordering).
1170 =head2 Want to know if find_or_create found or created a row?
1172 Just use C<find_or_new> instead, then check C<in_storage>:
1174 my $obj = $rs->find_or_new({ blah => 'blarg' });
1175 unless ($obj->in_storage) {
1177 # do whatever else you wanted if it was a new row
1180 =head3 Wrapping/overloading a column accessor
1182 Problem: Say you have a table "Camera" and want to associate a description
1183 with each camera. For most cameras, you'll be able to generate the description from
1184 the other columns. However, in a few special cases you may want to associate a
1185 custom description with a camera.
1189 In your database schema, define a description field in the "Camera" table that
1190 can contain text and null values.
1192 In DBIC, we'll overload the column accessor to provide a sane default if no
1193 custom description is defined. The accessor will either return or generate the
1194 description, depending on whether the field is null or not.
1196 First, in your "Camera" schema class, define the description field as follows:
1198 __PACKAGE__->add_columns(description => { accessor => '_description' });
1200 Next, we'll define the accessor-wrapper subroutine:
1205 # If there is an update to the column, we'll let the original accessor
1207 return $self->_description(@_) if @_;
1209 # Fetch the column value.
1210 my $description = $self->_description;
1212 # If there's something in the description field, then just return that.
1213 return $description if defined $description && length $descripton;
1215 # Otherwise, generate a description.
1216 return $self->generate_description;