3 DBIx::Class::Manual::Cookbook - Miscellaneous recipes
9 When you expect a large number of results, you can ask L<DBIx::Class> for a
10 paged resultset, which will fetch only a defined number of records at a time:
12 my $rs = $schema->resultset('Artist')->search(
15 page => 1, # page to return (defaults to 1)
16 rows => 10, # number of results per page
20 return $rs->all(); # all records for page 1
22 return $rs->page(2); # records for page 2
24 You can get a L<Data::Page> object for the resultset (suitable for use
25 in e.g. a template) using the C<pager> method:
29 =head2 Complex WHERE clauses
31 Sometimes you need to formulate a query using specific operators:
33 my @albums = $schema->resultset('Album')->search({
34 artist => { 'like', '%Lamb%' },
35 title => { 'like', '%Fear of Fours%' },
38 This results in something like the following C<WHERE> clause:
40 WHERE artist LIKE ? AND title LIKE ?
42 And the following bind values for the placeholders: C<'%Lamb%'>, C<'%Fear of
45 Other queries might require slightly more complex logic:
47 my @albums = $schema->resultset('Album')->search({
50 artist => { 'like', '%Smashing Pumpkins%' },
51 title => 'Siamese Dream',
53 artist => 'Starchildren',
57 This results in the following C<WHERE> clause:
59 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
60 OR artist = 'Starchildren'
62 For more information on generating complex queries, see
63 L<SQL::Abstract/WHERE CLAUSES>.
65 =head2 Retrieve one and only one row from a resultset
67 Sometimes you need only the first "top" row of a resultset. While this
68 can be easily done with L<< $rs->first|DBIx::Class::ResultSet/first
69 >>, it is suboptimal, as a full blown cursor for the resultset will be
70 created and then immediately destroyed after fetching the first row
71 object. L<< $rs->single|DBIx::Class::ResultSet/single >> is designed
72 specifically for this case - it will grab the first returned result
73 without even instantiating a cursor.
75 Before replacing all your calls to C<first()> with C<single()> please observe the
82 While single() takes a search condition just like search() does, it does
83 _not_ accept search attributes. However one can always chain a single() to
86 my $top_cd = $cd_rs->search({}, { order_by => 'rating' })->single;
91 Since single() is the engine behind find(), it is designed to fetch a
92 single row per database query. Thus a warning will be issued when the
93 underlying SELECT returns more than one row. Sometimes however this usage
94 is valid: i.e. we have an arbitrary number of cd's but only one of them is
95 at the top of the charts at any given time. If you know what you are doing,
96 you can silence the warning by explicitly limiting the resultset size:
98 my $top_cd = $cd_rs->search ({}, { order_by => 'rating', rows => 1 })->single;
102 =head2 Arbitrary SQL through a custom ResultSource
104 Sometimes you have to run arbitrary SQL because your query is too complex
105 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
106 be optimized for your database in a special way, but you still want to
107 get the results as a L<DBIx::Class::ResultSet>.
109 This is accomplished by defining a
110 L<ResultSource::View|DBIx::Class::ResultSource::View> for your query,
111 almost like you would define a regular ResultSource.
113 package My::Schema::Result::UserFriendsComplex;
116 use base qw/DBIx::Class/;
118 __PACKAGE__->load_components('Core');
119 __PACKAGE__->table_class('DBIx::Class::ResultSource::View');
121 # ->table, ->add_columns, etc.
123 # do not attempt to deploy() this view
124 __PACKAGE__->result_source_instance->is_virtual(1);
126 __PACKAGE__->result_source_instance->view_definition(q[
127 SELECT u.* FROM user u
128 INNER JOIN user_friends f ON u.id = f.user_id
129 WHERE f.friend_user_id = ?
131 SELECT u.* FROM user u
132 INNER JOIN user_friends f ON u.id = f.friend_user_id
136 Next, you can execute your complex query using bind parameters like this:
138 my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
140 bind => [ 12345, 12345 ]
144 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
145 that you cannot modify the rows it contains, ie. cannot call L</update>,
146 L</delete>, ... on it).
148 Note that you cannot have bind parameters unless is_virtual is set to true.
154 If you're using the old deprecated C<< $rsrc_instance->name(\'( SELECT ...') >>
155 method for custom SQL execution, you are highly encouraged to update your code
156 to use a virtual view as above. If you do not want to change your code, and just
157 want to suppress the deprecation warning when you call
158 L<DBIx::Class::Schema/deploy>, add this line to your source definition, so that
159 C<deploy> will exclude this "table":
161 sub sqlt_deploy_hook { $_[1]->schema->drop_table ($_[1]) }
165 =head2 Using specific columns
167 When you only want specific columns from a table, you can use
168 C<columns> to specify which ones you need. This is useful to avoid
169 loading columns with large amounts of data that you aren't about to
172 my $rs = $schema->resultset('Artist')->search(
175 columns => [qw/ name /]
180 # SELECT artist.name FROM artist
182 This is a shortcut for C<select> and C<as>, see below. C<columns>
183 cannot be used together with C<select> and C<as>.
185 =head2 Using database functions or stored procedures
187 The combination of C<select> and C<as> can be used to return the result of a
188 database function or stored procedure as a column value. You use C<select> to
189 specify the source for your column value (e.g. a column name, function, or
190 stored procedure name). You then use C<as> to set the column name you will use
191 to access the returned value:
193 my $rs = $schema->resultset('Artist')->search(
196 select => [ 'name', { LENGTH => 'name' } ],
197 as => [qw/ name name_length /],
202 # SELECT name name, LENGTH( name )
205 Note that the C<as> attribute B<has absolutely nothing to do> with the sql
206 syntax C< SELECT foo AS bar > (see the documentation in
207 L<DBIx::Class::ResultSet/ATTRIBUTES>). You can control the C<AS> part of the
208 generated SQL via the C<-as> field attribute as follows:
210 my $rs = $schema->resultset('Artist')->search(
215 '+select' => [ { count => 'cds.cdid', -as => 'amount_of_cds' } ],
216 '+as' => [qw/num_cds/],
217 order_by => { -desc => 'amount_of_cds' },
222 # SELECT me.artistid, me.name, me.rank, me.charfield, COUNT( cds.cdid ) AS amount_of_cds
223 # FROM artist me LEFT JOIN cd cds ON cds.artist = me.artistid
224 # GROUP BY me.artistid, me.name, me.rank, me.charfield
225 # ORDER BY amount_of_cds DESC
228 If your alias exists as a column in your base class (i.e. it was added with
229 L<add_columns|DBIx::Class::ResultSource/add_columns>), you just access it as
230 normal. Our C<Artist> class has a C<name> column, so we just use the C<name>
233 my $artist = $rs->first();
234 my $name = $artist->name();
236 If on the other hand the alias does not correspond to an existing column, you
237 have to fetch the value using the C<get_column> accessor:
239 my $name_length = $artist->get_column('name_length');
241 If you don't like using C<get_column>, you can always create an accessor for
242 any of your aliases using either of these:
244 # Define accessor manually:
245 sub name_length { shift->get_column('name_length'); }
247 # Or use DBIx::Class::AccessorGroup:
248 __PACKAGE__->mk_group_accessors('column' => 'name_length');
250 See also L</Using SQL functions on the left hand side of a comparison>.
252 =head2 SELECT DISTINCT with multiple columns
254 my $rs = $schema->resultset('Artist')->search(
257 columns => [ qw/artist_id name rank/ ],
262 my $rs = $schema->resultset('Artist')->search(
265 columns => [ qw/artist_id name rank/ ],
266 group_by => [ qw/artist_id name rank/ ],
271 # SELECT me.artist_id, me.name, me.rank
273 # GROUP BY artist_id, name, rank
275 =head2 SELECT COUNT(DISTINCT colname)
277 my $rs = $schema->resultset('Artist')->search(
280 columns => [ qw/name/ ],
285 my $rs = $schema->resultset('Artist')->search(
288 columns => [ qw/name/ ],
289 group_by => [ qw/name/ ],
293 my $count = $rs->count;
296 # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) count_subq:
298 =head2 Grouping results
300 L<DBIx::Class> supports C<GROUP BY> as follows:
302 my $rs = $schema->resultset('Artist')->search(
306 select => [ 'name', { count => 'cds.id' } ],
307 as => [qw/ name cd_count /],
308 group_by => [qw/ name /]
313 # SELECT name, COUNT( cd.id ) FROM artist
314 # LEFT JOIN cd ON artist.id = cd.artist
317 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
318 are in any way unsure about the use of the attributes above (C< join
319 >, C< select >, C< as > and C< group_by >).
321 =head2 Subqueries (EXPERIMENTAL)
323 You can write subqueries relatively easily in DBIC.
325 my $inside_rs = $schema->resultset('Artist')->search({
326 name => [ 'Billy Joel', 'Brittany Spears' ],
329 my $rs = $schema->resultset('CD')->search({
330 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
333 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
335 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
336 The following will B<not> work:
338 my $rs = $schema->resultset('CD')->search({
339 artist_id => $inside_rs->get_column('id')->as_query, # does NOT work
344 Subqueries are supported in the where clause (first hashref), and in the
345 from, select, and +select attributes.
347 =head3 Correlated subqueries
349 my $cdrs = $schema->resultset('CD');
350 my $rs = $cdrs->search({
352 '=' => $cdrs->search(
353 { artist_id => { '=' => \'me.artist_id' } },
355 )->get_column('year')->max_rs->as_query,
359 That creates the following SQL:
361 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
364 SELECT MAX(inner.year)
366 WHERE artist_id = me.artist_id
371 Please note that subqueries are considered an experimental feature.
373 =head2 Predefined searches
375 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
376 and defining often used searches as methods:
378 package My::DBIC::ResultSet::CD;
381 use base 'DBIx::Class::ResultSet';
383 sub search_cds_ordered {
386 return $self->search(
388 { order_by => 'name DESC' },
394 To use your resultset, first tell DBIx::Class to create an instance of it
395 for you, in your My::DBIC::Schema::CD class:
397 # class definition as normal
398 __PACKAGE__->load_components(qw/ Core /);
399 __PACKAGE__->table('cd');
401 # tell DBIC to use the custom ResultSet class
402 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
404 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
406 Then call your new method in your code:
408 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
410 =head2 Using SQL functions on the left hand side of a comparison
412 Using SQL functions on the left hand side of a comparison is generally not a
413 good idea since it requires a scan of the entire table. (Unless your RDBMS
414 supports indexes on expressions - including return values of functions -, and
415 you create an index on the return value of the function in question.) However,
416 it can be accomplished with C<DBIx::Class> when necessary.
418 If you do not have quoting on, simply include the function in your search
419 specification as you would any column:
421 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
423 With quoting on, or for a more portable solution, use literal SQL values with
426 $rs->search(\[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ]);
429 # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
433 -nest => \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ],
437 # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
439 Note: the C<plain_value> string in the C<< [ plain_value => 1979 ] >> part
440 should be either the same as the name of the column (do this if the type of the
441 return value of the function is the same as the type of the column) or
442 otherwise it's essentially a dummy string currently (use C<plain_value> as a
443 habit). It is used by L<DBIx::Class> to handle special column types.
445 See also L<SQL::Abstract/Literal SQL with placeholders and bind values
448 =head1 JOINS AND PREFETCHING
450 =head2 Using joins and prefetch
452 You can use the C<join> attribute to allow searching on, or sorting your
453 results by, one or more columns in a related table.
455 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
457 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
459 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
461 my $rs = $schema->resultset('CD')->search(
463 'artists.name' => 'Bob Marley'
466 join => 'artists', # join the artist table
471 # SELECT cd.* FROM cd
472 # JOIN artist ON cd.artist = artist.id
473 # WHERE artist.name = 'Bob Marley'
475 In that example both the join, and the condition use the relationship name rather than the table name
476 (see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
478 If required, you can now sort on any column in the related tables by including
479 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
481 my $rs = $schema->resultset('CD')->search(
483 'artists.name' => 'Bob Marley'
487 order_by => [qw/ artists.name /]
492 # SELECT cd.* FROM cd
493 # JOIN artist ON cd.artist = artist.id
494 # WHERE artist.name = 'Bob Marley'
495 # ORDER BY artist.name
497 Note that the C<join> attribute should only be used when you need to search or
498 sort using columns in a related table. Joining related tables when you only
499 need columns from the main table will make performance worse!
501 Now let's say you want to display a list of CDs, each with the name of the
502 artist. The following will work fine:
504 while (my $cd = $rs->next) {
505 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
508 There is a problem however. We have searched both the C<cd> and C<artist> tables
509 in our main query, but we have only returned data from the C<cd> table. To get
510 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
513 SELECT artist.* FROM artist WHERE artist.id = ?
515 A statement like the one above will run for each and every CD returned by our
516 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
519 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
520 This allows you to fetch results from related tables in advance:
522 my $rs = $schema->resultset('CD')->search(
524 'artists.name' => 'Bob Marley'
528 order_by => [qw/ artists.name /],
529 prefetch => 'artists' # return artist data too!
533 # Equivalent SQL (note SELECT from both "cd" and "artist"):
534 # SELECT cd.*, artist.* FROM cd
535 # JOIN artist ON cd.artist = artist.id
536 # WHERE artist.name = 'Bob Marley'
537 # ORDER BY artist.name
539 The code to print the CD list remains the same:
541 while (my $cd = $rs->next) {
542 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
545 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
546 so no additional SQL statements are executed. You now have a much more
549 Also note that C<prefetch> should only be used when you know you will
550 definitely use data from a related table. Pre-fetching related tables when you
551 only need columns from the main table will make performance worse!
553 =head2 Multiple joins
555 In the examples above, the C<join> attribute was a scalar. If you
556 pass an array reference instead, you can join to multiple tables. In
557 this example, we want to limit the search further, using
560 # Relationships defined elsewhere:
561 # CD->belongs_to('artist' => 'Artist');
562 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
563 my $rs = $schema->resultset('CD')->search(
565 'artist.name' => 'Bob Marley'
566 'liner_notes.notes' => { 'like', '%some text%' },
569 join => [qw/ artist liner_notes /],
570 order_by => [qw/ artist.name /],
575 # SELECT cd.*, artist.*, liner_notes.* FROM cd
576 # JOIN artist ON cd.artist = artist.id
577 # JOIN liner_notes ON cd.id = liner_notes.cd
578 # WHERE artist.name = 'Bob Marley'
579 # ORDER BY artist.name
581 =head2 Multi-step joins
583 Sometimes you want to join more than one relationship deep. In this example,
584 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
585 contain a specific string:
587 # Relationships defined elsewhere:
588 # Artist->has_many('cds' => 'CD', 'artist');
589 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
591 my $rs = $schema->resultset('Artist')->search(
593 'liner_notes.notes' => { 'like', '%some text%' },
597 'cds' => 'liner_notes'
603 # SELECT artist.* FROM artist
604 # LEFT JOIN cd ON artist.id = cd.artist
605 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
606 # WHERE liner_notes.notes LIKE '%some text%'
608 Joins can be nested to an arbitrary level. So if we decide later that we
609 want to reduce the number of Artists returned based on who wrote the liner
612 # Relationship defined elsewhere:
613 # LinerNotes->belongs_to('author' => 'Person');
615 my $rs = $schema->resultset('Artist')->search(
617 'liner_notes.notes' => { 'like', '%some text%' },
618 'author.name' => 'A. Writer'
623 'liner_notes' => 'author'
630 # SELECT artist.* FROM artist
631 # LEFT JOIN cd ON artist.id = cd.artist
632 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
633 # LEFT JOIN author ON author.id = liner_notes.author
634 # WHERE liner_notes.notes LIKE '%some text%'
635 # AND author.name = 'A. Writer'
637 =head2 Multi-step and multiple joins
639 With various combinations of array and hash references, you can join
640 tables in any combination you desire. For example, to join Artist to
641 CD and Concert, and join CD to LinerNotes:
643 # Relationships defined elsewhere:
644 # Artist->has_many('concerts' => 'Concert', 'artist');
646 my $rs = $schema->resultset('Artist')->search(
659 # SELECT artist.* FROM artist
660 # LEFT JOIN cd ON artist.id = cd.artist
661 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
662 # LEFT JOIN concert ON artist.id = concert.artist
664 =head2 Multi-step prefetch
666 C<prefetch> can be nested more than one relationship
667 deep using the same syntax as a multi-step join:
669 my $rs = $schema->resultset('Tag')->search(
679 # SELECT tag.*, cd.*, artist.* FROM tag
680 # JOIN cd ON tag.cd = cd.id
681 # JOIN artist ON cd.artist = artist.id
683 Now accessing our C<cd> and C<artist> relationships does not need additional
686 my $tag = $rs->first;
687 print $tag->cd->artist->name;
689 =head1 ROW-LEVEL OPERATIONS
691 =head2 Retrieving a row object's Schema
693 It is possible to get a Schema object from a row object like so:
695 my $schema = $cd->result_source->schema;
696 # use the schema as normal:
697 my $artist_rs = $schema->resultset('Artist');
699 This can be useful when you don't want to pass around a Schema object to every
702 =head2 Getting the value of the primary key for the last database insert
704 AKA getting last_insert_id
706 Thanks to the core component PK::Auto, this is straightforward:
708 my $foo = $rs->create(\%blah);
710 my $id = $foo->id; # foo->my_primary_key_field will also work.
712 If you are not using autoincrementing primary keys, this will probably
713 not work, but then you already know the value of the last primary key anyway.
715 =head2 Stringification
717 Employ the standard stringification technique by using the L<overload>
720 To make an object stringify itself as a single column, use something
721 like this (replace C<name> with the column/method of your choice):
723 use overload '""' => sub { shift->name}, fallback => 1;
725 For more complex stringification, you can use an anonymous subroutine:
727 use overload '""' => sub { $_[0]->name . ", " .
728 $_[0]->address }, fallback => 1;
730 =head3 Stringification Example
732 Suppose we have two tables: C<Product> and C<Category>. The table
735 Product(id, Description, category)
736 Category(id, Description)
738 C<category> is a foreign key into the Category table.
740 If you have a Product object C<$obj> and write something like
744 things will not work as expected.
746 To obtain, for example, the category description, you should add this
747 method to the class defining the Category table:
749 use overload "" => sub {
752 return $self->Description;
755 =head2 Want to know if find_or_create found or created a row?
757 Just use C<find_or_new> instead, then check C<in_storage>:
759 my $obj = $rs->find_or_new({ blah => 'blarg' });
760 unless ($obj->in_storage) {
762 # do whatever else you wanted if it was a new row
765 =head2 Static sub-classing DBIx::Class result classes
767 AKA adding additional relationships/methods/etc. to a model for a
768 specific usage of the (shared) model.
772 package My::App::Schema;
774 use base DBIx::Class::Schema;
776 # load subclassed classes from My::App::Schema::Result/ResultSet
777 __PACKAGE__->load_namespaces;
779 # load classes from shared model
781 'My::Shared::Model::Result' => [qw/
788 B<Result-Subclass definition>
790 package My::App::Schema::Result::Baz;
794 use base My::Shared::Model::Result::Baz;
796 # WARNING: Make sure you call table() again in your subclass,
797 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
798 # and the class name is not correctly registered as a source
799 __PACKAGE__->table('baz');
801 sub additional_method {
802 return "I'm an additional method only needed by this app";
807 =head2 Dynamic Sub-classing DBIx::Class proxy classes
809 AKA multi-class object inflation from one table
811 L<DBIx::Class> classes are proxy classes, therefore some different
812 techniques need to be employed for more than basic subclassing. In
813 this example we have a single user table that carries a boolean bit
814 for admin. We would like like to give the admin users
815 objects (L<DBIx::Class::Row>) the same methods as a regular user but
816 also special admin only methods. It doesn't make sense to create two
817 seperate proxy-class files for this. We would be copying all the user
818 methods into the Admin class. There is a cleaner way to accomplish
821 Overriding the C<inflate_result> method within the User proxy-class
822 gives us the effect we want. This method is called by
823 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
824 grab the object being returned, inspect the values we are looking for,
825 bless it if it's an admin object, and then return it. See the example
832 use base qw/DBIx::Class::Schema/;
834 __PACKAGE__->load_namespaces;
839 B<Proxy-Class definitions>
841 package My::Schema::Result::User;
845 use base qw/DBIx::Class/;
847 ### Define what our admin class is, for ensure_class_loaded()
848 my $admin_class = __PACKAGE__ . '::Admin';
850 __PACKAGE__->load_components(qw/Core/);
852 __PACKAGE__->table('users');
854 __PACKAGE__->add_columns(qw/user_id email password
855 firstname lastname active
858 __PACKAGE__->set_primary_key('user_id');
862 my $ret = $self->next::method(@_);
863 if( $ret->admin ) {### If this is an admin, rebless for extra functions
864 $self->ensure_class_loaded( $admin_class );
865 bless $ret, $admin_class;
871 print "I am a regular user.\n";
878 package My::Schema::Result::User::Admin;
882 use base qw/My::Schema::Result::User/;
884 # This line is important
885 __PACKAGE__->table('users');
889 print "I am an admin.\n";
895 print "I am doing admin stuff\n";
907 my $user_data = { email => 'someguy@place.com',
911 my $admin_data = { email => 'someadmin@adminplace.com',
915 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
917 $schema->resultset('User')->create( $user_data );
918 $schema->resultset('User')->create( $admin_data );
920 ### Now we search for them
921 my $user = $schema->resultset('User')->single( $user_data );
922 my $admin = $schema->resultset('User')->single( $admin_data );
924 print ref $user, "\n";
925 print ref $admin, "\n";
927 print $user->password , "\n"; # pass1
928 print $admin->password , "\n";# pass2; inherited from User
929 print $user->hello , "\n";# I am a regular user.
930 print $admin->hello, "\n";# I am an admin.
932 ### The statement below will NOT print
933 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
934 ### The statement below will print
935 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
937 Alternatively you can use L<DBIx::Class::DynamicSubclass> that implements
938 exactly the above functionality.
940 =head2 Skip row object creation for faster results
942 DBIx::Class is not built for speed, it's built for convenience and
943 ease of use, but sometimes you just need to get the data, and skip the
946 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
948 my $rs = $schema->resultset('CD');
950 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
952 my $hash_ref = $rs->find(1);
956 Beware, changing the Result class using
957 L<DBIx::Class::ResultSet/result_class> will replace any existing class
958 completely including any special components loaded using
959 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
961 =head2 Get raw data for blindingly fast results
963 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
964 above is not fast enough for you, you can use a DBIx::Class to return values
965 exactly as they come out of the database with none of the convenience methods
968 This is used like so:
970 my $cursor = $rs->cursor
971 while (my @vals = $cursor->next) {
972 # use $val[0..n] here
975 You will need to map the array offsets to particular columns (you can
976 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
978 =head1 RESULTSET OPERATIONS
980 =head2 Getting Schema from a ResultSet
982 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
984 $rs->result_source->schema
986 =head2 Getting Columns Of Data
990 If you want to find the sum of a particular column there are several
991 ways, the obvious one is to use search:
993 my $rs = $schema->resultset('Items')->search(
996 select => [ { sum => 'Cost' } ],
997 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
1000 my $tc = $rs->first->get_column('total_cost');
1002 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
1003 returned when you ask the C<ResultSet> for a column using
1006 my $cost = $schema->resultset('Items')->get_column('Cost');
1007 my $tc = $cost->sum;
1009 With this you can also do:
1011 my $minvalue = $cost->min;
1012 my $maxvalue = $cost->max;
1014 Or just iterate through the values of this column only:
1016 while ( my $c = $cost->next ) {
1020 foreach my $c ($cost->all) {
1024 C<ResultSetColumn> only has a limited number of built-in functions. If
1025 you need one that it doesn't have, then you can use the C<func> method
1028 my $avg = $cost->func('AVERAGE');
1030 This will cause the following SQL statement to be run:
1032 SELECT AVERAGE(Cost) FROM Items me
1034 Which will of course only work if your database supports this function.
1035 See L<DBIx::Class::ResultSetColumn> for more documentation.
1037 =head2 Creating a result set from a set of rows
1039 Sometimes you have a (set of) row objects that you want to put into a
1040 resultset without the need to hit the DB again. You can do that by using the
1041 L<set_cache|DBIx::Class::Resultset/set_cache> method:
1043 my @uploadable_groups;
1044 while (my $group = $groups->next) {
1045 if ($group->can_upload($self)) {
1046 push @uploadable_groups, $group;
1049 my $new_rs = $self->result_source->resultset;
1050 $new_rs->set_cache(\@uploadable_groups);
1054 =head1 USING RELATIONSHIPS
1056 =head2 Create a new row in a related table
1058 my $author = $book->create_related('author', { name => 'Fred'});
1060 =head2 Search in a related table
1062 Only searches for books named 'Titanic' by the author in $author.
1064 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1066 =head2 Delete data in a related table
1068 Deletes only the book named Titanic by the author in $author.
1070 $author->delete_related('books', { name => 'Titanic' });
1072 =head2 Ordering a relationship result set
1074 If you always want a relation to be ordered, you can specify this when you
1075 create the relationship.
1077 To order C<< $book->pages >> by descending page_number, create the relation
1080 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
1082 =head2 Filtering a relationship result set
1084 If you want to get a filtered result set, you can just add add to $attr as follows:
1086 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1088 =head2 Many-to-many relationships
1090 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1093 use base 'DBIx::Class';
1094 __PACKAGE__->load_components('Core');
1095 __PACKAGE__->table('user');
1096 __PACKAGE__->add_columns(qw/id name/);
1097 __PACKAGE__->set_primary_key('id');
1098 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1099 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1101 package My::UserAddress;
1102 use base 'DBIx::Class';
1103 __PACKAGE__->load_components('Core');
1104 __PACKAGE__->table('user_address');
1105 __PACKAGE__->add_columns(qw/user address/);
1106 __PACKAGE__->set_primary_key(qw/user address/);
1107 __PACKAGE__->belongs_to('user' => 'My::User');
1108 __PACKAGE__->belongs_to('address' => 'My::Address');
1110 package My::Address;
1111 use base 'DBIx::Class';
1112 __PACKAGE__->load_components('Core');
1113 __PACKAGE__->table('address');
1114 __PACKAGE__->add_columns(qw/id street town area_code country/);
1115 __PACKAGE__->set_primary_key('id');
1116 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1117 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1119 $rs = $user->addresses(); # get all addresses for a user
1120 $rs = $address->users(); # get all users for an address
1122 my $address = $user->add_to_addresses( # returns a My::Address instance,
1123 # NOT a My::UserAddress instance!
1125 country => 'United Kingdom',
1132 =head2 Relationships across DB schemas
1134 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1135 is easy as long as the schemas themselves are all accessible via the same DBI
1136 connection. In most cases, this means that they are on the same database host
1137 as each other and your connecting database user has the proper permissions to them.
1139 To accomplish this one only needs to specify the DB schema name in the table
1140 declaration, like so...
1142 package MyDatabase::Main::Artist;
1143 use base qw/DBIx::Class/;
1144 __PACKAGE__->load_components(qw/PK::Auto Core/);
1146 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1148 __PACKAGE__->add_columns(qw/ artist_id name /);
1149 __PACKAGE__->set_primary_key('artist_id');
1150 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1154 Whatever string you specify there will be used to build the "FROM" clause in SQL
1157 The big drawback to this is you now have DB schema names hardcoded in your
1158 class files. This becomes especially troublesome if you have multiple instances
1159 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1160 the DB schemas are named based on the environment (e.g. database1_dev).
1162 However, one can dynamically "map" to the proper DB schema by overriding the
1163 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1164 building a renaming facility, like so:
1166 package MyDatabase::Schema;
1169 extends 'DBIx::Class::Schema';
1171 around connection => sub {
1172 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1174 my $postfix = delete $attr->{schema_name_postfix};
1179 $self->append_db_name($postfix);
1183 sub append_db_name {
1184 my ( $self, $postfix ) = @_;
1188 { $_->name =~ /^\w+\./mx }
1190 { $self->source($_) }
1193 foreach my $source (@sources_with_db) {
1194 my $name = $source->name;
1195 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1197 $source->name($name);
1203 By overridding the L<connection|DBIx::Class::Schama/connection>
1204 method and extracting a custom option from the provided \%attr hashref one can
1205 then simply iterate over all the Schema's ResultSources, renaming them as
1208 To use this facility, simply add or modify the \%attr hashref that is passed to
1209 L<connection|DBIx::Class::Schama/connect>, as follows:
1212 = MyDatabase::Schema->connect(
1217 schema_name_postfix => '_dev'
1218 # ... Other options as desired ...
1221 Obviously, one could accomplish even more advanced mapping via a hash map or a
1226 As of version 0.04001, there is improved transaction support in
1227 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1228 example of the recommended way to use it:
1230 my $genus = $schema->resultset('Genus')->find(12);
1232 my $coderef2 = sub {
1237 my $coderef1 = sub {
1238 $genus->add_to_species({ name => 'troglodyte' });
1241 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1242 return $genus->species;
1247 $rs = $schema->txn_do($coderef1);
1250 if ($@) { # Transaction failed
1251 die "the sky is falling!" #
1252 if ($@ =~ /Rollback failed/); # Rollback failed
1254 deal_with_failed_transaction();
1257 Nested transactions will work as expected. That is, only the outermost
1258 transaction will actually issue a commit to the $dbh, and a rollback
1259 at any level of any transaction will cause the entire nested
1260 transaction to fail.
1262 =head2 Nested transactions and auto-savepoints
1264 If savepoints are supported by your RDBMS, it is possible to achieve true
1265 nested transactions with minimal effort. To enable auto-savepoints via nested
1266 transactions, supply the C<< auto_savepoint = 1 >> connection attribute.
1268 Here is an example of true nested transactions. In the example, we start a big
1269 task which will create several rows. Generation of data for each row is a
1270 fragile operation and might fail. If we fail creating something, depending on
1271 the type of failure, we want to abort the whole task, or only skip the failed
1274 my $schema = MySchema->connect("dbi:Pg:dbname=my_db");
1276 # Start a transaction. Every database change from here on will only be
1277 # commited into the database if the eval block succeeds.
1279 $schema->txn_do(sub {
1282 my $job = $schema->resultset('Job')->create({ name=> 'big job' });
1283 # SQL: INSERT INTO job ( name) VALUES ( 'big job' );
1287 # Start a nested transaction, which in fact sets a savepoint.
1289 $schema->txn_do(sub {
1290 # SQL: SAVEPOINT savepoint_0;
1292 my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
1293 # SQL: INSERT INTO thing ( job) VALUES ( 1 );
1296 # This will generate an error, thus setting $@
1298 $thing->update({force_fail=>'foo'});
1299 # SQL: UPDATE thing SET force_fail = 'foo'
1300 # WHERE ( id = 42 );
1305 # SQL: ROLLBACK TO SAVEPOINT savepoint_0;
1307 # There was an error while creating a $thing. Depending on the error
1308 # we want to abort the whole transaction, or only rollback the
1309 # changes related to the creation of this $thing
1311 # Abort the whole job
1312 if ($@ =~ /horrible_problem/) {
1313 print "something horrible happend, aborting job!";
1314 die $@; # rethrow error
1317 # Ignore this $thing, report the error, and continue with the
1319 print "Cannot create thing: $@";
1321 # There was no error, so save all changes since the last
1324 # SQL: RELEASE SAVEPOINT savepoint_0;
1329 # There was an error while handling the $job. Rollback all changes
1330 # since the transaction started, including the already commited
1331 # ('released') savepoints. There will be neither a new $job nor any
1332 # $thing entry in the database.
1336 print "ERROR: $@\n";
1339 # There was no error while handling the $job. Commit all changes.
1340 # Only now other connections can see the newly created $job and
1348 In this example it might be hard to see where the rollbacks, releases and
1349 commits are happening, but it works just the same as for plain L<<txn_do>>: If
1350 the C<eval>-block around C<txn_do> fails, a rollback is issued. If the C<eval>
1351 succeeds, the transaction is committed (or the savepoint released).
1353 While you can get more fine-grained controll using C<svp_begin>, C<svp_release>
1354 and C<svp_rollback>, it is strongly recommended to use C<txn_do> with coderefs.
1358 =head2 Creating Schemas From An Existing Database
1360 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1361 L<DBIx::Class::Schema> and associated sources by examining the database.
1363 The recommend way of achieving this is to use the
1364 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1366 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1367 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1369 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1370 source definitions for all the tables found in the C<foo> database.
1372 =head2 Creating DDL SQL
1374 The following functionality requires you to have L<SQL::Translator>
1375 (also known as "SQL Fairy") installed.
1377 To create a set of database-specific .sql files for the above schema:
1379 my $schema = My::Schema->connect($dsn);
1380 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1385 By default this will create schema files in the current directory, for
1386 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1388 To create a new database using the schema:
1390 my $schema = My::Schema->connect($dsn);
1391 $schema->deploy({ add_drop_tables => 1});
1393 To import created .sql files using the mysql client:
1395 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1397 To create C<ALTER TABLE> conversion scripts to update a database to a
1398 newer version of your schema at a later point, first set a new
1399 C<$VERSION> in your Schema file, then:
1401 my $schema = My::Schema->connect($dsn);
1402 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1408 This will produce new database-specific .sql files for the new version
1409 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1410 requires that the files for 0.1 as created above are available in the
1411 given directory to diff against.
1413 =head2 Select from dual
1415 Dummy tables are needed by some databases to allow calling functions
1416 or expressions that aren't based on table content, for examples of how
1417 this applies to various database types, see:
1418 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1420 Note: If you're using Oracles dual table don't B<ever> do anything
1421 other than a select, if you CRUD on your dual table you *will* break
1424 Make a table class as you would for any other table
1426 package MyAppDB::Dual;
1429 use base 'DBIx::Class';
1430 __PACKAGE__->load_components("Core");
1431 __PACKAGE__->table("Dual");
1432 __PACKAGE__->add_columns(
1434 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1437 Once you've loaded your table class select from it using C<select>
1438 and C<as> instead of C<columns>
1440 my $rs = $schema->resultset('Dual')->search(undef,
1441 { select => [ 'sydate' ],
1446 All you have to do now is be careful how you access your resultset, the below
1447 will not work because there is no column called 'now' in the Dual table class
1449 while (my $dual = $rs->next) {
1450 print $dual->now."\n";
1452 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1454 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1455 your Dual class for whatever you wanted to select from dual, but that's just
1456 silly, instead use C<get_column>
1458 while (my $dual = $rs->next) {
1459 print $dual->get_column('now')."\n";
1464 my $cursor = $rs->cursor;
1465 while (my @vals = $cursor->next) {
1466 print $vals[0]."\n";
1469 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1470 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1471 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1472 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1473 L<SQL::Translator> to not create table dual:
1476 add_drop_table => 1,
1477 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1479 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1481 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1483 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1484 while ( my $dual = $rs->next ) {
1485 print $dual->{now}."\n";
1488 Here are some example C<select> conditions to illustrate the different syntax
1489 you could use for doing stuff like
1490 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1492 # get a sequence value
1493 select => [ 'A_SEQ.nextval' ],
1495 # get create table sql
1496 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1498 # get a random num between 0 and 100
1499 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1502 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1505 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1507 # which day of the week were you born on?
1508 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1510 # select 16 rows from dual
1511 select => [ "'hello'" ],
1513 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1517 =head2 Adding Indexes And Functions To Your SQL
1519 Often you will want indexes on columns on your table to speed up searching. To
1520 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1521 class (refer to the advanced
1522 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1523 to share a hook between multiple sources):
1525 package My::Schema::Result::Artist;
1527 __PACKAGE__->table('artist');
1528 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1530 sub sqlt_deploy_hook {
1531 my ($self, $sqlt_table) = @_;
1533 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1538 Sometimes you might want to change the index depending on the type of the
1539 database for which SQL is being generated:
1541 my ($db_type = $sqlt_table->schema->translator->producer_type)
1542 =~ s/^SQL::Translator::Producer:://;
1544 You can also add hooks to the schema level to stop certain tables being
1551 sub sqlt_deploy_hook {
1552 my ($self, $sqlt_schema) = @_;
1554 $sqlt_schema->drop_table('table_name');
1557 You could also add views, procedures or triggers to the output using
1558 L<SQL::Translator::Schema/add_view>,
1559 L<SQL::Translator::Schema/add_procedure> or
1560 L<SQL::Translator::Schema/add_trigger>.
1563 =head2 Schema versioning
1565 The following example shows simplistically how you might use DBIx::Class to
1566 deploy versioned schemas to your customers. The basic process is as follows:
1572 Create a DBIx::Class schema
1584 Modify schema to change functionality
1588 Deploy update to customers
1592 B<Create a DBIx::Class schema>
1594 This can either be done manually, or generated from an existing database as
1595 described under L</Creating Schemas From An Existing Database>
1599 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1601 B<Deploy to customers>
1603 There are several ways you could deploy your schema. These are probably
1604 beyond the scope of this recipe, but might include:
1610 Require customer to apply manually using their RDBMS.
1614 Package along with your app, making database dump/schema update/tests
1615 all part of your install.
1619 B<Modify the schema to change functionality>
1621 As your application evolves, it may be necessary to modify your schema
1622 to change functionality. Once the changes are made to your schema in
1623 DBIx::Class, export the modified schema and the conversion scripts as
1624 in L</Creating DDL SQL>.
1626 B<Deploy update to customers>
1628 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1629 Schema class. This will add a new table to your database called
1630 C<dbix_class_schema_vesion> which will keep track of which version is installed
1631 and warn if the user trys to run a newer schema version than the
1632 database thinks it has.
1634 Alternatively, you can send the conversion sql scripts to your
1637 =head2 Setting quoting for the generated SQL
1639 If the database contains column names with spaces and/or reserved words, they
1640 need to be quoted in the SQL queries. This is done using:
1642 $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
1643 $schema->storage->sql_maker->name_sep('.');
1645 The first sets the quote characters. Either a pair of matching
1646 brackets, or a C<"> or C<'>:
1648 $schema->storage->sql_maker->quote_char('"');
1650 Check the documentation of your database for the correct quote
1651 characters to use. C<name_sep> needs to be set to allow the SQL
1652 generator to put the quotes the correct place.
1654 In most cases you should set these as part of the arguments passed to
1655 L<DBIx::Class::Schema/connect>:
1657 my $schema = My::Schema->connect(
1667 In some cases, quoting will be required for all users of a schema. To enforce
1668 this, you can also overload the C<connection> method for your schema class:
1672 my $rv = $self->next::method( @_ );
1673 $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
1674 $rv->storage->sql_maker->name_sep('.');
1678 =head2 Setting limit dialect for SQL::Abstract::Limit
1680 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1681 the remote SQL server by looking at the database handle. This is a
1682 common problem when using the DBD::JDBC, since the DBD-driver only
1683 know that in has a Java-driver available, not which JDBC driver the
1684 Java component has loaded. This specifically sets the limit_dialect
1685 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1688 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1690 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1691 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1693 The limit dialect can also be set at connect time by specifying a
1694 C<limit_dialect> key in the final hash as shown above.
1696 =head2 Working with PostgreSQL array types
1698 You can also assign values to PostgreSQL array columns by passing array
1699 references in the C<\%columns> (C<\%vals>) hashref of the
1700 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1703 $resultset->create({
1704 numbers => [1, 2, 3]
1709 numbers => [1, 2, 3]
1716 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1717 methods) you cannot directly use array references (since this is interpreted as
1718 a list of values to be C<OR>ed), but you can use the following syntax to force
1719 passing them as bind values:
1723 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1727 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1728 placeholders and bind values (subqueries)> for more explanation. Note that
1729 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1730 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1731 arrayrefs together with the column name, like this: C<< [column_name => value]
1734 =head1 BOOTSTRAPPING/MIGRATING
1736 =head2 Easy migration from class-based to schema-based setup
1738 You want to start using the schema-based approach to L<DBIx::Class>
1739 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1740 of existing classes that you don't want to move by hand. Try this nifty script
1744 use SQL::Translator;
1746 my $schema = MyDB->schema_instance;
1748 my $translator = SQL::Translator->new(
1749 debug => $debug || 0,
1750 trace => $trace || 0,
1751 no_comments => $no_comments || 0,
1752 show_warnings => $show_warnings || 0,
1753 add_drop_table => $add_drop_table || 0,
1754 validate => $validate || 0,
1756 'DBIx::Schema' => $schema,
1759 'prefix' => 'My::Schema',
1763 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1764 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1766 my $output = $translator->translate(@args) or die
1767 "Error: " . $translator->error;
1771 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1772 namespace, which is currently left as an exercise for the reader.
1774 =head1 OVERLOADING METHODS
1776 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1777 method calls, useful for things like default values and triggers. You have to
1778 use calls to C<next::method> to overload methods. More information on using
1779 L<Class::C3> with L<DBIx::Class> can be found in
1780 L<DBIx::Class::Manual::Component>.
1782 =head2 Setting default values for a row
1784 It's as simple as overriding the C<new> method. Note the use of
1788 my ( $class, $attrs ) = @_;
1790 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1792 my $new = $class->next::method($attrs);
1797 For more information about C<next::method>, look in the L<Class::C3>
1798 documentation. See also L<DBIx::Class::Manual::Component> for more
1799 ways to write your own base classes to do this.
1801 People looking for ways to do "triggers" with DBIx::Class are probably
1802 just looking for this.
1804 =head2 Changing one field whenever another changes
1806 For example, say that you have three columns, C<id>, C<number>, and
1807 C<squared>. You would like to make changes to C<number> and have
1808 C<squared> be automagically set to the value of C<number> squared.
1809 You can accomplish this by overriding C<store_column>:
1812 my ( $self, $name, $value ) = @_;
1813 if ($name eq 'number') {
1814 $self->squared($value * $value);
1816 $self->next::method($name, $value);
1819 Note that the hard work is done by the call to C<next::method>, which
1820 redispatches your call to store_column in the superclass(es).
1822 =head2 Automatically creating related objects
1824 You might have a class C<Artist> which has many C<CD>s. Further, you
1825 want to create a C<CD> object every time you insert an C<Artist> object.
1826 You can accomplish this by overriding C<insert> on your objects:
1829 my ( $self, @args ) = @_;
1830 $self->next::method(@args);
1831 $self->cds->new({})->fill_from_artist($self)->insert;
1835 where C<fill_from_artist> is a method you specify in C<CD> which sets
1836 values in C<CD> based on the data in the C<Artist> object you pass in.
1838 =head2 Wrapping/overloading a column accessor
1842 Say you have a table "Camera" and want to associate a description
1843 with each camera. For most cameras, you'll be able to generate the description from
1844 the other columns. However, in a few special cases you may want to associate a
1845 custom description with a camera.
1849 In your database schema, define a description field in the "Camera" table that
1850 can contain text and null values.
1852 In DBIC, we'll overload the column accessor to provide a sane default if no
1853 custom description is defined. The accessor will either return or generate the
1854 description, depending on whether the field is null or not.
1856 First, in your "Camera" schema class, define the description field as follows:
1858 __PACKAGE__->add_columns(description => { accessor => '_description' });
1860 Next, we'll define the accessor-wrapper subroutine:
1865 # If there is an update to the column, we'll let the original accessor
1867 return $self->_description(@_) if @_;
1869 # Fetch the column value.
1870 my $description = $self->_description;
1872 # If there's something in the description field, then just return that.
1873 return $description if defined $description && length $descripton;
1875 # Otherwise, generate a description.
1876 return $self->generate_description;
1879 =head1 DEBUGGING AND PROFILING
1881 =head2 DBIx::Class objects with Data::Dumper
1883 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1884 be hard to find the pertinent data in all the data it can generate.
1885 Specifically, if one naively tries to use it like so,
1889 my $cd = $schema->resultset('CD')->find(1);
1892 several pages worth of data from the CD object's schema and result source will
1893 be dumped to the screen. Since usually one is only interested in a few column
1894 values of the object, this is not very helpful.
1896 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1897 it. Simply define a hook that L<Data::Dumper> will call on the object before
1898 dumping it. For example,
1905 result_source => undef,
1913 local $Data::Dumper::Freezer = '_dumper_hook';
1915 my $cd = $schema->resultset('CD')->find(1);
1917 # dumps $cd without its ResultSource
1919 If the structure of your schema is such that there is a common base class for
1920 all your table classes, simply put a method similar to C<_dumper_hook> in the
1921 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1922 will automagically clean up your data before printing it. See
1923 L<Data::Dumper/EXAMPLES> for more information.
1927 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1928 executed as well as notifications of query completion and transaction
1929 begin/commit. If you'd like to profile the SQL you can subclass the
1930 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1933 package My::Profiler;
1936 use base 'DBIx::Class::Storage::Statistics';
1938 use Time::HiRes qw(time);
1947 $self->print("Executing $sql: ".join(', ', @params)."\n");
1956 my $elapsed = sprintf("%0.4f", time() - $start);
1957 $self->print("Execution took $elapsed seconds.\n");
1963 You can then install that class as the debugging object:
1965 __PACKAGE__->storage->debugobj(new My::Profiler());
1966 __PACKAGE__->storage->debug(1);
1968 A more complicated example might involve storing each execution of SQL in an
1976 my $elapsed = time() - $start;
1977 push(@{ $calls{$sql} }, {
1983 You could then create average, high and low execution times for an SQL
1984 statement and dig down to see if certain parameters cause aberrant behavior.
1985 You might want to check out L<DBIx::Class::QueryLog> as well.
1987 =head1 STARTUP SPEED
1989 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1990 as the ORM loads all the relevant classes. This section examines
1991 techniques for reducing the startup delay.
1993 These tips are are listed in order of decreasing effectiveness - so the
1994 first tip, if applicable, should have the greatest effect on your
1997 =head2 Statically Define Your Schema
2000 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
2001 classes dynamically based on the database schema then there will be a
2002 significant startup delay.
2004 For production use a statically defined schema (which can be generated
2005 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
2006 the database schema once - see
2007 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
2008 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
2009 details on creating static schemas from a database).
2011 =head2 Move Common Startup into a Base Class
2013 Typically L<DBIx::Class> result classes start off with
2015 use base qw/DBIx::Class/;
2016 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
2018 If this preamble is moved into a common base class:-
2022 use base qw/DBIx::Class/;
2023 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
2026 and each result class then uses this as a base:-
2028 use base qw/MyDBICbase/;
2030 then the load_components is only performed once, which can result in a
2031 considerable startup speedup for schemas with many classes.
2033 =head2 Explicitly List Schema Result Classes
2035 The schema class will normally contain
2037 __PACKAGE__->load_classes();
2039 to load the result classes. This will use L<Module::Find|Module::Find>
2040 to find and load the appropriate modules. Explicitly defining the
2041 classes you wish to load will remove the overhead of
2042 L<Module::Find|Module::Find> and the related directory operations:
2044 __PACKAGE__->load_classes(qw/ CD Artist Track /);
2046 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
2047 syntax to load the appropriate classes there is not a direct alternative
2048 avoiding L<Module::Find|Module::Find>.
2052 =head2 Cached statements
2054 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
2055 This is normally a good idea, but if too many statements are cached, the database may use too much
2056 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
2057 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
2059 # print all currently cached prepared statements
2060 print for keys %{$schema->storage->dbh->{CachedKids}};
2061 # get a count of currently cached prepared statements
2062 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
2064 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
2067 my $kids = $schema->storage->dbh->{CachedKids};
2068 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
2070 But what you probably want is to expire unused statements and not those that are used frequently.
2071 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
2075 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
2076 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },