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::Core/;
118 __PACKAGE__->table_class('DBIx::Class::ResultSource::View');
120 # ->table, ->add_columns, etc.
122 # do not attempt to deploy() this view
123 __PACKAGE__->result_source_instance->is_virtual(1);
125 __PACKAGE__->result_source_instance->view_definition(q[
126 SELECT u.* FROM user u
127 INNER JOIN user_friends f ON u.id = f.user_id
128 WHERE f.friend_user_id = ?
130 SELECT u.* FROM user u
131 INNER JOIN user_friends f ON u.id = f.friend_user_id
135 Next, you can execute your complex query using bind parameters like this:
137 my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
139 bind => [ 12345, 12345 ]
143 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
144 that you cannot modify the rows it contains, ie. cannot call L</update>,
145 L</delete>, ... on it).
147 Note that you cannot have bind parameters unless is_virtual is set to true.
153 If you're using the old deprecated C<< $rsrc_instance->name(\'( SELECT ...') >>
154 method for custom SQL execution, you are highly encouraged to update your code
155 to use a virtual view as above. If you do not want to change your code, and just
156 want to suppress the deprecation warning when you call
157 L<DBIx::Class::Schema/deploy>, add this line to your source definition, so that
158 C<deploy> will exclude this "table":
160 sub sqlt_deploy_hook { $_[1]->schema->drop_table ($_[1]) }
164 =head2 Using specific columns
166 When you only want specific columns from a table, you can use
167 C<columns> to specify which ones you need. This is useful to avoid
168 loading columns with large amounts of data that you aren't about to
171 my $rs = $schema->resultset('Artist')->search(
174 columns => [qw/ name /]
179 # SELECT artist.name FROM artist
181 This is a shortcut for C<select> and C<as>, see below. C<columns>
182 cannot be used together with C<select> and C<as>.
184 =head2 Using database functions or stored procedures
186 The combination of C<select> and C<as> can be used to return the result of a
187 database function or stored procedure as a column value. You use C<select> to
188 specify the source for your column value (e.g. a column name, function, or
189 stored procedure name). You then use C<as> to set the column name you will use
190 to access the returned value:
192 my $rs = $schema->resultset('Artist')->search(
195 select => [ 'name', { LENGTH => 'name' } ],
196 as => [qw/ name name_length /],
201 # SELECT name name, LENGTH( name )
204 Note that the C<as> attribute B<has absolutely nothing to do> with the sql
205 syntax C< SELECT foo AS bar > (see the documentation in
206 L<DBIx::Class::ResultSet/ATTRIBUTES>). You can control the C<AS> part of the
207 generated SQL via the C<-as> field attribute as follows:
209 my $rs = $schema->resultset('Artist')->search(
214 '+select' => [ { count => 'cds.cdid', -as => 'amount_of_cds' } ],
215 '+as' => [qw/num_cds/],
216 order_by => { -desc => 'amount_of_cds' },
221 # SELECT me.artistid, me.name, me.rank, me.charfield, COUNT( cds.cdid ) AS amount_of_cds
222 # FROM artist me LEFT JOIN cd cds ON cds.artist = me.artistid
223 # GROUP BY me.artistid, me.name, me.rank, me.charfield
224 # ORDER BY amount_of_cds DESC
227 If your alias exists as a column in your base class (i.e. it was added with
228 L<add_columns|DBIx::Class::ResultSource/add_columns>), you just access it as
229 normal. Our C<Artist> class has a C<name> column, so we just use the C<name>
232 my $artist = $rs->first();
233 my $name = $artist->name();
235 If on the other hand the alias does not correspond to an existing column, you
236 have to fetch the value using the C<get_column> accessor:
238 my $name_length = $artist->get_column('name_length');
240 If you don't like using C<get_column>, you can always create an accessor for
241 any of your aliases using either of these:
243 # Define accessor manually:
244 sub name_length { shift->get_column('name_length'); }
246 # Or use DBIx::Class::AccessorGroup:
247 __PACKAGE__->mk_group_accessors('column' => 'name_length');
249 See also L</Using SQL functions on the left hand side of a comparison>.
251 =head2 SELECT DISTINCT with multiple columns
253 my $rs = $schema->resultset('Artist')->search(
256 columns => [ qw/artist_id name rank/ ],
261 my $rs = $schema->resultset('Artist')->search(
264 columns => [ qw/artist_id name rank/ ],
265 group_by => [ qw/artist_id name rank/ ],
270 # SELECT me.artist_id, me.name, me.rank
272 # GROUP BY artist_id, name, rank
274 =head2 SELECT COUNT(DISTINCT colname)
276 my $rs = $schema->resultset('Artist')->search(
279 columns => [ qw/name/ ],
284 my $rs = $schema->resultset('Artist')->search(
287 columns => [ qw/name/ ],
288 group_by => [ qw/name/ ],
292 my $count = $rs->count;
295 # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) count_subq:
297 =head2 Grouping results
299 L<DBIx::Class> supports C<GROUP BY> as follows:
301 my $rs = $schema->resultset('Artist')->search(
305 select => [ 'name', { count => 'cds.id' } ],
306 as => [qw/ name cd_count /],
307 group_by => [qw/ name /]
312 # SELECT name, COUNT( cd.id ) FROM artist
313 # LEFT JOIN cd ON artist.id = cd.artist
316 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
317 are in any way unsure about the use of the attributes above (C< join
318 >, C< select >, C< as > and C< group_by >).
320 =head2 Subqueries (EXPERIMENTAL)
322 You can write subqueries relatively easily in DBIC.
324 my $inside_rs = $schema->resultset('Artist')->search({
325 name => [ 'Billy Joel', 'Brittany Spears' ],
328 my $rs = $schema->resultset('CD')->search({
329 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
332 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
334 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
335 The following will B<not> work:
337 my $rs = $schema->resultset('CD')->search({
338 artist_id => $inside_rs->get_column('id')->as_query, # does NOT work
343 Subqueries are supported in the where clause (first hashref), and in the
344 from, select, and +select attributes.
346 =head3 Correlated subqueries
348 my $cdrs = $schema->resultset('CD');
349 my $rs = $cdrs->search({
351 '=' => $cdrs->search(
352 { artist_id => { '=' => \'me.artist_id' } },
354 )->get_column('year')->max_rs->as_query,
358 That creates the following SQL:
360 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
363 SELECT MAX(inner.year)
365 WHERE artist_id = me.artist_id
370 Please note that subqueries are considered an experimental feature.
372 =head2 Predefined searches
374 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
375 and defining often used searches as methods:
377 package My::DBIC::ResultSet::CD;
380 use base 'DBIx::Class::ResultSet';
382 sub search_cds_ordered {
385 return $self->search(
387 { order_by => 'name DESC' },
393 If you're using L<DBIx::Class::Schema/load_namespaces>, simply place the file
394 into the C<ResultSet> directory next to your C<Result> directory, and it will
395 be automatically loaded.
397 If however you are still using L<DBIx::Class::Schema/load_classes>, first tell
398 DBIx::Class to create an instance of the ResultSet class for you, in your
399 My::DBIC::Schema::CD class:
401 # class definition as normal
402 use base 'DBIx::Class::Core';
403 __PACKAGE__->table('cd');
405 # tell DBIC to use the custom ResultSet class
406 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
408 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
410 Then call your new method in your code:
412 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
414 =head2 Using SQL functions on the left hand side of a comparison
416 Using SQL functions on the left hand side of a comparison is generally not a
417 good idea since it requires a scan of the entire table. (Unless your RDBMS
418 supports indexes on expressions - including return values of functions -, and
419 you create an index on the return value of the function in question.) However,
420 it can be accomplished with C<DBIx::Class> when necessary.
422 If you do not have quoting on, simply include the function in your search
423 specification as you would any column:
425 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
427 With quoting on, or for a more portable solution, use literal SQL values with
430 $rs->search(\[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ]);
433 # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
437 -nest => \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ],
441 # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
443 Note: the C<plain_value> string in the C<< [ plain_value => 1979 ] >> part
444 should be either the same as the name of the column (do this if the type of the
445 return value of the function is the same as the type of the column) or
446 otherwise it's essentially a dummy string currently (use C<plain_value> as a
447 habit). It is used by L<DBIx::Class> to handle special column types.
449 See also L<SQL::Abstract/Literal SQL with placeholders and bind values
452 =head1 JOINS AND PREFETCHING
454 =head2 Using joins and prefetch
456 You can use the C<join> attribute to allow searching on, or sorting your
457 results by, one or more columns in a related table.
459 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
461 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
463 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
465 my $rs = $schema->resultset('CD')->search(
467 'artists.name' => 'Bob Marley'
470 join => 'artists', # join the artist table
475 # SELECT cd.* FROM cd
476 # JOIN artist ON cd.artist = artist.id
477 # WHERE artist.name = 'Bob Marley'
479 In that example both the join, and the condition use the relationship name rather than the table name
480 (see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
482 If required, you can now sort on any column in the related tables by including
483 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
485 my $rs = $schema->resultset('CD')->search(
487 'artists.name' => 'Bob Marley'
491 order_by => [qw/ artists.name /]
496 # SELECT cd.* FROM cd
497 # JOIN artist ON cd.artist = artist.id
498 # WHERE artist.name = 'Bob Marley'
499 # ORDER BY artist.name
501 Note that the C<join> attribute should only be used when you need to search or
502 sort using columns in a related table. Joining related tables when you only
503 need columns from the main table will make performance worse!
505 Now let's say you want to display a list of CDs, each with the name of the
506 artist. The following will work fine:
508 while (my $cd = $rs->next) {
509 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
512 There is a problem however. We have searched both the C<cd> and C<artist> tables
513 in our main query, but we have only returned data from the C<cd> table. To get
514 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
517 SELECT artist.* FROM artist WHERE artist.id = ?
519 A statement like the one above will run for each and every CD returned by our
520 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
523 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
524 This allows you to fetch results from related tables in advance:
526 my $rs = $schema->resultset('CD')->search(
528 'artists.name' => 'Bob Marley'
532 order_by => [qw/ artists.name /],
533 prefetch => 'artists' # return artist data too!
537 # Equivalent SQL (note SELECT from both "cd" and "artist"):
538 # SELECT cd.*, artist.* FROM cd
539 # JOIN artist ON cd.artist = artist.id
540 # WHERE artist.name = 'Bob Marley'
541 # ORDER BY artist.name
543 The code to print the CD list remains the same:
545 while (my $cd = $rs->next) {
546 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
549 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
550 so no additional SQL statements are executed. You now have a much more
553 Also note that C<prefetch> should only be used when you know you will
554 definitely use data from a related table. Pre-fetching related tables when you
555 only need columns from the main table will make performance worse!
557 =head2 Multiple joins
559 In the examples above, the C<join> attribute was a scalar. If you
560 pass an array reference instead, you can join to multiple tables. In
561 this example, we want to limit the search further, using
564 # Relationships defined elsewhere:
565 # CD->belongs_to('artist' => 'Artist');
566 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
567 my $rs = $schema->resultset('CD')->search(
569 'artist.name' => 'Bob Marley'
570 'liner_notes.notes' => { 'like', '%some text%' },
573 join => [qw/ artist liner_notes /],
574 order_by => [qw/ artist.name /],
579 # SELECT cd.*, artist.*, liner_notes.* FROM cd
580 # JOIN artist ON cd.artist = artist.id
581 # JOIN liner_notes ON cd.id = liner_notes.cd
582 # WHERE artist.name = 'Bob Marley'
583 # ORDER BY artist.name
585 =head2 Multi-step joins
587 Sometimes you want to join more than one relationship deep. In this example,
588 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
589 contain a specific string:
591 # Relationships defined elsewhere:
592 # Artist->has_many('cds' => 'CD', 'artist');
593 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
595 my $rs = $schema->resultset('Artist')->search(
597 'liner_notes.notes' => { 'like', '%some text%' },
601 'cds' => 'liner_notes'
607 # SELECT artist.* FROM artist
608 # LEFT JOIN cd ON artist.id = cd.artist
609 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
610 # WHERE liner_notes.notes LIKE '%some text%'
612 Joins can be nested to an arbitrary level. So if we decide later that we
613 want to reduce the number of Artists returned based on who wrote the liner
616 # Relationship defined elsewhere:
617 # LinerNotes->belongs_to('author' => 'Person');
619 my $rs = $schema->resultset('Artist')->search(
621 'liner_notes.notes' => { 'like', '%some text%' },
622 'author.name' => 'A. Writer'
627 'liner_notes' => 'author'
634 # SELECT artist.* FROM artist
635 # LEFT JOIN cd ON artist.id = cd.artist
636 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
637 # LEFT JOIN author ON author.id = liner_notes.author
638 # WHERE liner_notes.notes LIKE '%some text%'
639 # AND author.name = 'A. Writer'
641 =head2 Multi-step and multiple joins
643 With various combinations of array and hash references, you can join
644 tables in any combination you desire. For example, to join Artist to
645 CD and Concert, and join CD to LinerNotes:
647 # Relationships defined elsewhere:
648 # Artist->has_many('concerts' => 'Concert', 'artist');
650 my $rs = $schema->resultset('Artist')->search(
663 # SELECT artist.* FROM artist
664 # LEFT JOIN cd ON artist.id = cd.artist
665 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
666 # LEFT JOIN concert ON artist.id = concert.artist
668 =head2 Multi-step prefetch
670 C<prefetch> can be nested more than one relationship
671 deep using the same syntax as a multi-step join:
673 my $rs = $schema->resultset('Tag')->search(
683 # SELECT tag.*, cd.*, artist.* FROM tag
684 # JOIN cd ON tag.cd = cd.id
685 # JOIN artist ON cd.artist = artist.id
687 Now accessing our C<cd> and C<artist> relationships does not need additional
690 my $tag = $rs->first;
691 print $tag->cd->artist->name;
693 =head1 ROW-LEVEL OPERATIONS
695 =head2 Retrieving a row object's Schema
697 It is possible to get a Schema object from a row object like so:
699 my $schema = $cd->result_source->schema;
700 # use the schema as normal:
701 my $artist_rs = $schema->resultset('Artist');
703 This can be useful when you don't want to pass around a Schema object to every
706 =head2 Getting the value of the primary key for the last database insert
708 AKA getting last_insert_id
710 Thanks to the core component PK::Auto, this is straightforward:
712 my $foo = $rs->create(\%blah);
714 my $id = $foo->id; # foo->my_primary_key_field will also work.
716 If you are not using autoincrementing primary keys, this will probably
717 not work, but then you already know the value of the last primary key anyway.
719 =head2 Stringification
721 Employ the standard stringification technique by using the L<overload>
724 To make an object stringify itself as a single column, use something
725 like this (replace C<name> with the column/method of your choice):
727 use overload '""' => sub { shift->name}, fallback => 1;
729 For more complex stringification, you can use an anonymous subroutine:
731 use overload '""' => sub { $_[0]->name . ", " .
732 $_[0]->address }, fallback => 1;
734 =head3 Stringification Example
736 Suppose we have two tables: C<Product> and C<Category>. The table
739 Product(id, Description, category)
740 Category(id, Description)
742 C<category> is a foreign key into the Category table.
744 If you have a Product object C<$obj> and write something like
748 things will not work as expected.
750 To obtain, for example, the category description, you should add this
751 method to the class defining the Category table:
753 use overload "" => sub {
756 return $self->Description;
759 =head2 Want to know if find_or_create found or created a row?
761 Just use C<find_or_new> instead, then check C<in_storage>:
763 my $obj = $rs->find_or_new({ blah => 'blarg' });
764 unless ($obj->in_storage) {
766 # do whatever else you wanted if it was a new row
769 =head2 Static sub-classing DBIx::Class result classes
771 AKA adding additional relationships/methods/etc. to a model for a
772 specific usage of the (shared) model.
776 package My::App::Schema;
778 use base DBIx::Class::Schema;
780 # load subclassed classes from My::App::Schema::Result/ResultSet
781 __PACKAGE__->load_namespaces;
783 # load classes from shared model
785 'My::Shared::Model::Result' => [qw/
792 B<Result-Subclass definition>
794 package My::App::Schema::Result::Baz;
798 use base My::Shared::Model::Result::Baz;
800 # WARNING: Make sure you call table() again in your subclass,
801 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
802 # and the class name is not correctly registered as a source
803 __PACKAGE__->table('baz');
805 sub additional_method {
806 return "I'm an additional method only needed by this app";
811 =head2 Dynamic Sub-classing DBIx::Class proxy classes
813 AKA multi-class object inflation from one table
815 L<DBIx::Class> classes are proxy classes, therefore some different
816 techniques need to be employed for more than basic subclassing. In
817 this example we have a single user table that carries a boolean bit
818 for admin. We would like like to give the admin users
819 objects (L<DBIx::Class::Row>) the same methods as a regular user but
820 also special admin only methods. It doesn't make sense to create two
821 seperate proxy-class files for this. We would be copying all the user
822 methods into the Admin class. There is a cleaner way to accomplish
825 Overriding the C<inflate_result> method within the User proxy-class
826 gives us the effect we want. This method is called by
827 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
828 grab the object being returned, inspect the values we are looking for,
829 bless it if it's an admin object, and then return it. See the example
836 use base qw/DBIx::Class::Schema/;
838 __PACKAGE__->load_namespaces;
843 B<Proxy-Class definitions>
845 package My::Schema::Result::User;
849 use base qw/DBIx::Class::Core/;
851 ### Define what our admin class is, for ensure_class_loaded()
852 my $admin_class = __PACKAGE__ . '::Admin';
854 __PACKAGE__->table('users');
856 __PACKAGE__->add_columns(qw/user_id email password
857 firstname lastname active
860 __PACKAGE__->set_primary_key('user_id');
864 my $ret = $self->next::method(@_);
865 if( $ret->admin ) {### If this is an admin, rebless for extra functions
866 $self->ensure_class_loaded( $admin_class );
867 bless $ret, $admin_class;
873 print "I am a regular user.\n";
880 package My::Schema::Result::User::Admin;
884 use base qw/My::Schema::Result::User/;
886 # This line is important
887 __PACKAGE__->table('users');
891 print "I am an admin.\n";
897 print "I am doing admin stuff\n";
909 my $user_data = { email => 'someguy@place.com',
913 my $admin_data = { email => 'someadmin@adminplace.com',
917 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
919 $schema->resultset('User')->create( $user_data );
920 $schema->resultset('User')->create( $admin_data );
922 ### Now we search for them
923 my $user = $schema->resultset('User')->single( $user_data );
924 my $admin = $schema->resultset('User')->single( $admin_data );
926 print ref $user, "\n";
927 print ref $admin, "\n";
929 print $user->password , "\n"; # pass1
930 print $admin->password , "\n";# pass2; inherited from User
931 print $user->hello , "\n";# I am a regular user.
932 print $admin->hello, "\n";# I am an admin.
934 ### The statement below will NOT print
935 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
936 ### The statement below will print
937 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
939 Alternatively you can use L<DBIx::Class::DynamicSubclass> that implements
940 exactly the above functionality.
942 =head2 Skip row object creation for faster results
944 DBIx::Class is not built for speed, it's built for convenience and
945 ease of use, but sometimes you just need to get the data, and skip the
948 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
950 my $rs = $schema->resultset('CD');
952 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
954 my $hash_ref = $rs->find(1);
958 Beware, changing the Result class using
959 L<DBIx::Class::ResultSet/result_class> will replace any existing class
960 completely including any special components loaded using
961 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
963 =head2 Get raw data for blindingly fast results
965 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
966 above is not fast enough for you, you can use a DBIx::Class to return values
967 exactly as they come out of the database with none of the convenience methods
970 This is used like so:
972 my $cursor = $rs->cursor
973 while (my @vals = $cursor->next) {
974 # use $val[0..n] here
977 You will need to map the array offsets to particular columns (you can
978 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
980 =head1 RESULTSET OPERATIONS
982 =head2 Getting Schema from a ResultSet
984 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
986 $rs->result_source->schema
988 =head2 Getting Columns Of Data
992 If you want to find the sum of a particular column there are several
993 ways, the obvious one is to use search:
995 my $rs = $schema->resultset('Items')->search(
998 select => [ { sum => 'Cost' } ],
999 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
1002 my $tc = $rs->first->get_column('total_cost');
1004 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
1005 returned when you ask the C<ResultSet> for a column using
1008 my $cost = $schema->resultset('Items')->get_column('Cost');
1009 my $tc = $cost->sum;
1011 With this you can also do:
1013 my $minvalue = $cost->min;
1014 my $maxvalue = $cost->max;
1016 Or just iterate through the values of this column only:
1018 while ( my $c = $cost->next ) {
1022 foreach my $c ($cost->all) {
1026 C<ResultSetColumn> only has a limited number of built-in functions. If
1027 you need one that it doesn't have, then you can use the C<func> method
1030 my $avg = $cost->func('AVERAGE');
1032 This will cause the following SQL statement to be run:
1034 SELECT AVERAGE(Cost) FROM Items me
1036 Which will of course only work if your database supports this function.
1037 See L<DBIx::Class::ResultSetColumn> for more documentation.
1039 =head2 Creating a result set from a set of rows
1041 Sometimes you have a (set of) row objects that you want to put into a
1042 resultset without the need to hit the DB again. You can do that by using the
1043 L<set_cache|DBIx::Class::Resultset/set_cache> method:
1045 my @uploadable_groups;
1046 while (my $group = $groups->next) {
1047 if ($group->can_upload($self)) {
1048 push @uploadable_groups, $group;
1051 my $new_rs = $self->result_source->resultset;
1052 $new_rs->set_cache(\@uploadable_groups);
1056 =head1 USING RELATIONSHIPS
1058 =head2 Create a new row in a related table
1060 my $author = $book->create_related('author', { name => 'Fred'});
1062 =head2 Search in a related table
1064 Only searches for books named 'Titanic' by the author in $author.
1066 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1068 =head2 Delete data in a related table
1070 Deletes only the book named Titanic by the author in $author.
1072 $author->delete_related('books', { name => 'Titanic' });
1074 =head2 Ordering a relationship result set
1076 If you always want a relation to be ordered, you can specify this when you
1077 create the relationship.
1079 To order C<< $book->pages >> by descending page_number, create the relation
1082 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
1084 =head2 Filtering a relationship result set
1086 If you want to get a filtered result set, you can just add add to $attr as follows:
1088 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1090 =head2 Many-to-many relationships
1092 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1095 use base 'DBIx::Class::Core';
1096 __PACKAGE__->table('user');
1097 __PACKAGE__->add_columns(qw/id name/);
1098 __PACKAGE__->set_primary_key('id');
1099 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1100 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1102 package My::UserAddress;
1103 use base 'DBIx::Class::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::Core';
1112 __PACKAGE__->table('address');
1113 __PACKAGE__->add_columns(qw/id street town area_code country/);
1114 __PACKAGE__->set_primary_key('id');
1115 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1116 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1118 $rs = $user->addresses(); # get all addresses for a user
1119 $rs = $address->users(); # get all users for an address
1121 my $address = $user->add_to_addresses( # returns a My::Address instance,
1122 # NOT a My::UserAddress instance!
1124 country => 'United Kingdom',
1131 =head2 Relationships across DB schemas
1133 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1134 is easy as long as the schemas themselves are all accessible via the same DBI
1135 connection. In most cases, this means that they are on the same database host
1136 as each other and your connecting database user has the proper permissions to them.
1138 To accomplish this one only needs to specify the DB schema name in the table
1139 declaration, like so...
1141 package MyDatabase::Main::Artist;
1142 use base qw/DBIx::Class::Core/;
1144 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1146 __PACKAGE__->add_columns(qw/ artist_id name /);
1147 __PACKAGE__->set_primary_key('artist_id');
1148 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1152 Whatever string you specify there will be used to build the "FROM" clause in SQL
1155 The big drawback to this is you now have DB schema names hardcoded in your
1156 class files. This becomes especially troublesome if you have multiple instances
1157 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1158 the DB schemas are named based on the environment (e.g. database1_dev).
1160 However, one can dynamically "map" to the proper DB schema by overriding the
1161 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1162 building a renaming facility, like so:
1164 package MyDatabase::Schema;
1167 extends 'DBIx::Class::Schema';
1169 around connection => sub {
1170 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1172 my $postfix = delete $attr->{schema_name_postfix};
1177 $self->append_db_name($postfix);
1181 sub append_db_name {
1182 my ( $self, $postfix ) = @_;
1186 { $_->name =~ /^\w+\./mx }
1188 { $self->source($_) }
1191 foreach my $source (@sources_with_db) {
1192 my $name = $source->name;
1193 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1195 $source->name($name);
1201 By overridding the L<connection|DBIx::Class::Schama/connection>
1202 method and extracting a custom option from the provided \%attr hashref one can
1203 then simply iterate over all the Schema's ResultSources, renaming them as
1206 To use this facility, simply add or modify the \%attr hashref that is passed to
1207 L<connection|DBIx::Class::Schama/connect>, as follows:
1210 = MyDatabase::Schema->connect(
1215 schema_name_postfix => '_dev'
1216 # ... Other options as desired ...
1219 Obviously, one could accomplish even more advanced mapping via a hash map or a
1224 As of version 0.04001, there is improved transaction support in
1225 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1226 example of the recommended way to use it:
1228 my $genus = $schema->resultset('Genus')->find(12);
1230 my $coderef2 = sub {
1235 my $coderef1 = sub {
1236 $genus->add_to_species({ name => 'troglodyte' });
1239 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1240 return $genus->species;
1245 $rs = $schema->txn_do($coderef1);
1248 if ($@) { # Transaction failed
1249 die "the sky is falling!" #
1250 if ($@ =~ /Rollback failed/); # Rollback failed
1252 deal_with_failed_transaction();
1255 Nested transactions will work as expected. That is, only the outermost
1256 transaction will actually issue a commit to the $dbh, and a rollback
1257 at any level of any transaction will cause the entire nested
1258 transaction to fail.
1260 =head2 Nested transactions and auto-savepoints
1262 If savepoints are supported by your RDBMS, it is possible to achieve true
1263 nested transactions with minimal effort. To enable auto-savepoints via nested
1264 transactions, supply the C<< auto_savepoint = 1 >> connection attribute.
1266 Here is an example of true nested transactions. In the example, we start a big
1267 task which will create several rows. Generation of data for each row is a
1268 fragile operation and might fail. If we fail creating something, depending on
1269 the type of failure, we want to abort the whole task, or only skip the failed
1272 my $schema = MySchema->connect("dbi:Pg:dbname=my_db");
1274 # Start a transaction. Every database change from here on will only be
1275 # commited into the database if the eval block succeeds.
1277 $schema->txn_do(sub {
1280 my $job = $schema->resultset('Job')->create({ name=> 'big job' });
1281 # SQL: INSERT INTO job ( name) VALUES ( 'big job' );
1285 # Start a nested transaction, which in fact sets a savepoint.
1287 $schema->txn_do(sub {
1288 # SQL: SAVEPOINT savepoint_0;
1290 my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
1291 # SQL: INSERT INTO thing ( job) VALUES ( 1 );
1294 # This will generate an error, thus setting $@
1296 $thing->update({force_fail=>'foo'});
1297 # SQL: UPDATE thing SET force_fail = 'foo'
1298 # WHERE ( id = 42 );
1303 # SQL: ROLLBACK TO SAVEPOINT savepoint_0;
1305 # There was an error while creating a $thing. Depending on the error
1306 # we want to abort the whole transaction, or only rollback the
1307 # changes related to the creation of this $thing
1309 # Abort the whole job
1310 if ($@ =~ /horrible_problem/) {
1311 print "something horrible happend, aborting job!";
1312 die $@; # rethrow error
1315 # Ignore this $thing, report the error, and continue with the
1317 print "Cannot create thing: $@";
1319 # There was no error, so save all changes since the last
1322 # SQL: RELEASE SAVEPOINT savepoint_0;
1327 # There was an error while handling the $job. Rollback all changes
1328 # since the transaction started, including the already commited
1329 # ('released') savepoints. There will be neither a new $job nor any
1330 # $thing entry in the database.
1334 print "ERROR: $@\n";
1337 # There was no error while handling the $job. Commit all changes.
1338 # Only now other connections can see the newly created $job and
1346 In this example it might be hard to see where the rollbacks, releases and
1347 commits are happening, but it works just the same as for plain L<<txn_do>>: If
1348 the C<eval>-block around C<txn_do> fails, a rollback is issued. If the C<eval>
1349 succeeds, the transaction is committed (or the savepoint released).
1351 While you can get more fine-grained controll using C<svp_begin>, C<svp_release>
1352 and C<svp_rollback>, it is strongly recommended to use C<txn_do> with coderefs.
1356 =head2 Creating Schemas From An Existing Database
1358 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1359 L<DBIx::Class::Schema> and associated sources by examining the database.
1361 The recommend way of achieving this is to use the
1362 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1364 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1365 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1367 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1368 source definitions for all the tables found in the C<foo> database.
1370 =head2 Creating DDL SQL
1372 The following functionality requires you to have L<SQL::Translator>
1373 (also known as "SQL Fairy") installed.
1375 To create a set of database-specific .sql files for the above schema:
1377 my $schema = My::Schema->connect($dsn);
1378 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1383 By default this will create schema files in the current directory, for
1384 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1386 To create a new database using the schema:
1388 my $schema = My::Schema->connect($dsn);
1389 $schema->deploy({ add_drop_table => 1});
1391 To import created .sql files using the mysql client:
1393 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1395 To create C<ALTER TABLE> conversion scripts to update a database to a
1396 newer version of your schema at a later point, first set a new
1397 C<$VERSION> in your Schema file, then:
1399 my $schema = My::Schema->connect($dsn);
1400 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1406 This will produce new database-specific .sql files for the new version
1407 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1408 requires that the files for 0.1 as created above are available in the
1409 given directory to diff against.
1411 =head2 Select from dual
1413 Dummy tables are needed by some databases to allow calling functions
1414 or expressions that aren't based on table content, for examples of how
1415 this applies to various database types, see:
1416 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1418 Note: If you're using Oracles dual table don't B<ever> do anything
1419 other than a select, if you CRUD on your dual table you *will* break
1422 Make a table class as you would for any other table
1424 package MyAppDB::Dual;
1427 use base 'DBIx::Class::Core';
1428 __PACKAGE__->table("Dual");
1429 __PACKAGE__->add_columns(
1431 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1434 Once you've loaded your table class select from it using C<select>
1435 and C<as> instead of C<columns>
1437 my $rs = $schema->resultset('Dual')->search(undef,
1438 { select => [ 'sydate' ],
1443 All you have to do now is be careful how you access your resultset, the below
1444 will not work because there is no column called 'now' in the Dual table class
1446 while (my $dual = $rs->next) {
1447 print $dual->now."\n";
1449 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1451 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1452 your Dual class for whatever you wanted to select from dual, but that's just
1453 silly, instead use C<get_column>
1455 while (my $dual = $rs->next) {
1456 print $dual->get_column('now')."\n";
1461 my $cursor = $rs->cursor;
1462 while (my @vals = $cursor->next) {
1463 print $vals[0]."\n";
1466 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1467 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1468 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1469 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1470 L<SQL::Translator> to not create table dual:
1473 add_drop_table => 1,
1474 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1476 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1478 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1480 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1481 while ( my $dual = $rs->next ) {
1482 print $dual->{now}."\n";
1485 Here are some example C<select> conditions to illustrate the different syntax
1486 you could use for doing stuff like
1487 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1489 # get a sequence value
1490 select => [ 'A_SEQ.nextval' ],
1492 # get create table sql
1493 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1495 # get a random num between 0 and 100
1496 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1499 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1502 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1504 # which day of the week were you born on?
1505 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1507 # select 16 rows from dual
1508 select => [ "'hello'" ],
1510 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1514 =head2 Adding Indexes And Functions To Your SQL
1516 Often you will want indexes on columns on your table to speed up searching. To
1517 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1518 class (refer to the advanced
1519 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1520 to share a hook between multiple sources):
1522 package My::Schema::Result::Artist;
1524 __PACKAGE__->table('artist');
1525 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1527 sub sqlt_deploy_hook {
1528 my ($self, $sqlt_table) = @_;
1530 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1535 Sometimes you might want to change the index depending on the type of the
1536 database for which SQL is being generated:
1538 my ($db_type = $sqlt_table->schema->translator->producer_type)
1539 =~ s/^SQL::Translator::Producer:://;
1541 You can also add hooks to the schema level to stop certain tables being
1548 sub sqlt_deploy_hook {
1549 my ($self, $sqlt_schema) = @_;
1551 $sqlt_schema->drop_table('table_name');
1554 You could also add views, procedures or triggers to the output using
1555 L<SQL::Translator::Schema/add_view>,
1556 L<SQL::Translator::Schema/add_procedure> or
1557 L<SQL::Translator::Schema/add_trigger>.
1560 =head2 Schema versioning
1562 The following example shows simplistically how you might use DBIx::Class to
1563 deploy versioned schemas to your customers. The basic process is as follows:
1569 Create a DBIx::Class schema
1581 Modify schema to change functionality
1585 Deploy update to customers
1589 B<Create a DBIx::Class schema>
1591 This can either be done manually, or generated from an existing database as
1592 described under L</Creating Schemas From An Existing Database>
1596 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1598 B<Deploy to customers>
1600 There are several ways you could deploy your schema. These are probably
1601 beyond the scope of this recipe, but might include:
1607 Require customer to apply manually using their RDBMS.
1611 Package along with your app, making database dump/schema update/tests
1612 all part of your install.
1616 B<Modify the schema to change functionality>
1618 As your application evolves, it may be necessary to modify your schema
1619 to change functionality. Once the changes are made to your schema in
1620 DBIx::Class, export the modified schema and the conversion scripts as
1621 in L</Creating DDL SQL>.
1623 B<Deploy update to customers>
1625 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1626 Schema class. This will add a new table to your database called
1627 C<dbix_class_schema_vesion> which will keep track of which version is installed
1628 and warn if the user trys to run a newer schema version than the
1629 database thinks it has.
1631 Alternatively, you can send the conversion sql scripts to your
1634 =head2 Setting quoting for the generated SQL
1636 If the database contains column names with spaces and/or reserved words, they
1637 need to be quoted in the SQL queries. This is done using:
1639 $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
1640 $schema->storage->sql_maker->name_sep('.');
1642 The first sets the quote characters. Either a pair of matching
1643 brackets, or a C<"> or C<'>:
1645 $schema->storage->sql_maker->quote_char('"');
1647 Check the documentation of your database for the correct quote
1648 characters to use. C<name_sep> needs to be set to allow the SQL
1649 generator to put the quotes the correct place.
1651 In most cases you should set these as part of the arguments passed to
1652 L<DBIx::Class::Schema/connect>:
1654 my $schema = My::Schema->connect(
1664 In some cases, quoting will be required for all users of a schema. To enforce
1665 this, you can also overload the C<connection> method for your schema class:
1669 my $rv = $self->next::method( @_ );
1670 $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
1671 $rv->storage->sql_maker->name_sep('.');
1675 =head2 Setting limit dialect for SQL::Abstract::Limit
1677 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1678 the remote SQL server by looking at the database handle. This is a
1679 common problem when using the DBD::JDBC, since the DBD-driver only
1680 know that in has a Java-driver available, not which JDBC driver the
1681 Java component has loaded. This specifically sets the limit_dialect
1682 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1685 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1687 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1688 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1690 The limit dialect can also be set at connect time by specifying a
1691 C<limit_dialect> key in the final hash as shown above.
1693 =head2 Working with PostgreSQL array types
1695 You can also assign values to PostgreSQL array columns by passing array
1696 references in the C<\%columns> (C<\%vals>) hashref of the
1697 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1700 $resultset->create({
1701 numbers => [1, 2, 3]
1706 numbers => [1, 2, 3]
1713 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1714 methods) you cannot directly use array references (since this is interpreted as
1715 a list of values to be C<OR>ed), but you can use the following syntax to force
1716 passing them as bind values:
1720 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1724 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1725 placeholders and bind values (subqueries)> for more explanation. Note that
1726 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1727 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1728 arrayrefs together with the column name, like this: C<< [column_name => value]
1731 =head1 BOOTSTRAPPING/MIGRATING
1733 =head2 Easy migration from class-based to schema-based setup
1735 You want to start using the schema-based approach to L<DBIx::Class>
1736 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1737 of existing classes that you don't want to move by hand. Try this nifty script
1741 use SQL::Translator;
1743 my $schema = MyDB->schema_instance;
1745 my $translator = SQL::Translator->new(
1746 debug => $debug || 0,
1747 trace => $trace || 0,
1748 no_comments => $no_comments || 0,
1749 show_warnings => $show_warnings || 0,
1750 add_drop_table => $add_drop_table || 0,
1751 validate => $validate || 0,
1753 'DBIx::Schema' => $schema,
1756 'prefix' => 'My::Schema',
1760 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1761 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1763 my $output = $translator->translate(@args) or die
1764 "Error: " . $translator->error;
1768 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1769 namespace, which is currently left as an exercise for the reader.
1771 =head1 OVERLOADING METHODS
1773 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1774 method calls, useful for things like default values and triggers. You have to
1775 use calls to C<next::method> to overload methods. More information on using
1776 L<Class::C3> with L<DBIx::Class> can be found in
1777 L<DBIx::Class::Manual::Component>.
1779 =head2 Setting default values for a row
1781 It's as simple as overriding the C<new> method. Note the use of
1785 my ( $class, $attrs ) = @_;
1787 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1789 my $new = $class->next::method($attrs);
1794 For more information about C<next::method>, look in the L<Class::C3>
1795 documentation. See also L<DBIx::Class::Manual::Component> for more
1796 ways to write your own base classes to do this.
1798 People looking for ways to do "triggers" with DBIx::Class are probably
1799 just looking for this.
1801 =head2 Changing one field whenever another changes
1803 For example, say that you have three columns, C<id>, C<number>, and
1804 C<squared>. You would like to make changes to C<number> and have
1805 C<squared> be automagically set to the value of C<number> squared.
1806 You can accomplish this by overriding C<store_column>:
1809 my ( $self, $name, $value ) = @_;
1810 if ($name eq 'number') {
1811 $self->squared($value * $value);
1813 $self->next::method($name, $value);
1816 Note that the hard work is done by the call to C<next::method>, which
1817 redispatches your call to store_column in the superclass(es).
1819 =head2 Automatically creating related objects
1821 You might have a class C<Artist> which has many C<CD>s. Further, you
1822 want to create a C<CD> object every time you insert an C<Artist> object.
1823 You can accomplish this by overriding C<insert> on your objects:
1826 my ( $self, @args ) = @_;
1827 $self->next::method(@args);
1828 $self->cds->new({})->fill_from_artist($self)->insert;
1832 where C<fill_from_artist> is a method you specify in C<CD> which sets
1833 values in C<CD> based on the data in the C<Artist> object you pass in.
1835 =head2 Wrapping/overloading a column accessor
1839 Say you have a table "Camera" and want to associate a description
1840 with each camera. For most cameras, you'll be able to generate the description from
1841 the other columns. However, in a few special cases you may want to associate a
1842 custom description with a camera.
1846 In your database schema, define a description field in the "Camera" table that
1847 can contain text and null values.
1849 In DBIC, we'll overload the column accessor to provide a sane default if no
1850 custom description is defined. The accessor will either return or generate the
1851 description, depending on whether the field is null or not.
1853 First, in your "Camera" schema class, define the description field as follows:
1855 __PACKAGE__->add_columns(description => { accessor => '_description' });
1857 Next, we'll define the accessor-wrapper subroutine:
1862 # If there is an update to the column, we'll let the original accessor
1864 return $self->_description(@_) if @_;
1866 # Fetch the column value.
1867 my $description = $self->_description;
1869 # If there's something in the description field, then just return that.
1870 return $description if defined $description && length $descripton;
1872 # Otherwise, generate a description.
1873 return $self->generate_description;
1876 =head1 DEBUGGING AND PROFILING
1878 =head2 DBIx::Class objects with Data::Dumper
1880 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1881 be hard to find the pertinent data in all the data it can generate.
1882 Specifically, if one naively tries to use it like so,
1886 my $cd = $schema->resultset('CD')->find(1);
1889 several pages worth of data from the CD object's schema and result source will
1890 be dumped to the screen. Since usually one is only interested in a few column
1891 values of the object, this is not very helpful.
1893 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1894 it. Simply define a hook that L<Data::Dumper> will call on the object before
1895 dumping it. For example,
1902 result_source => undef,
1910 local $Data::Dumper::Freezer = '_dumper_hook';
1912 my $cd = $schema->resultset('CD')->find(1);
1914 # dumps $cd without its ResultSource
1916 If the structure of your schema is such that there is a common base class for
1917 all your table classes, simply put a method similar to C<_dumper_hook> in the
1918 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1919 will automagically clean up your data before printing it. See
1920 L<Data::Dumper/EXAMPLES> for more information.
1924 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1925 executed as well as notifications of query completion and transaction
1926 begin/commit. If you'd like to profile the SQL you can subclass the
1927 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1930 package My::Profiler;
1933 use base 'DBIx::Class::Storage::Statistics';
1935 use Time::HiRes qw(time);
1944 $self->print("Executing $sql: ".join(', ', @params)."\n");
1953 my $elapsed = sprintf("%0.4f", time() - $start);
1954 $self->print("Execution took $elapsed seconds.\n");
1960 You can then install that class as the debugging object:
1962 __PACKAGE__->storage->debugobj(new My::Profiler());
1963 __PACKAGE__->storage->debug(1);
1965 A more complicated example might involve storing each execution of SQL in an
1973 my $elapsed = time() - $start;
1974 push(@{ $calls{$sql} }, {
1980 You could then create average, high and low execution times for an SQL
1981 statement and dig down to see if certain parameters cause aberrant behavior.
1982 You might want to check out L<DBIx::Class::QueryLog> as well.
1984 =head1 STARTUP SPEED
1986 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1987 as the ORM loads all the relevant classes. This section examines
1988 techniques for reducing the startup delay.
1990 These tips are are listed in order of decreasing effectiveness - so the
1991 first tip, if applicable, should have the greatest effect on your
1994 =head2 Statically Define Your Schema
1997 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1998 classes dynamically based on the database schema then there will be a
1999 significant startup delay.
2001 For production use a statically defined schema (which can be generated
2002 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
2003 the database schema once - see
2004 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
2005 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
2006 details on creating static schemas from a database).
2008 =head2 Move Common Startup into a Base Class
2010 Typically L<DBIx::Class> result classes start off with
2012 use base qw/DBIx::Class::Core/;
2013 __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2015 If this preamble is moved into a common base class:-
2019 use base qw/DBIx::Class::Core/;
2020 __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2023 and each result class then uses this as a base:-
2025 use base qw/MyDBICbase/;
2027 then the load_components is only performed once, which can result in a
2028 considerable startup speedup for schemas with many classes.
2030 =head2 Explicitly List Schema Result Classes
2032 The schema class will normally contain
2034 __PACKAGE__->load_classes();
2036 to load the result classes. This will use L<Module::Find|Module::Find>
2037 to find and load the appropriate modules. Explicitly defining the
2038 classes you wish to load will remove the overhead of
2039 L<Module::Find|Module::Find> and the related directory operations:
2041 __PACKAGE__->load_classes(qw/ CD Artist Track /);
2043 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
2044 syntax to load the appropriate classes there is not a direct alternative
2045 avoiding L<Module::Find|Module::Find>.
2049 =head2 Cached statements
2051 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
2052 This is normally a good idea, but if too many statements are cached, the database may use too much
2053 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
2054 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
2056 # print all currently cached prepared statements
2057 print for keys %{$schema->storage->dbh->{CachedKids}};
2058 # get a count of currently cached prepared statements
2059 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
2061 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
2064 my $kids = $schema->storage->dbh->{CachedKids};
2065 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
2067 But what you probably want is to expire unused statements and not those that are used frequently.
2068 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
2072 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
2073 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },