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, e.g. 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) me:
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 >).
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
368 =head2 Predefined searches
370 You can define frequently used searches as methods by subclassing
371 L<DBIx::Class::ResultSet>:
373 package My::DBIC::ResultSet::CD;
376 use base 'DBIx::Class::ResultSet';
378 sub search_cds_ordered {
381 return $self->search(
383 { order_by => 'name DESC' },
389 If you're using L<DBIx::Class::Schema/load_namespaces>, simply place the file
390 into the C<ResultSet> directory next to your C<Result> directory, and it will
391 be automatically loaded.
393 If however you are still using L<DBIx::Class::Schema/load_classes>, first tell
394 DBIx::Class to create an instance of the ResultSet class for you, in your
395 My::DBIC::Schema::CD class:
397 # class definition as normal
398 use base 'DBIx::Class::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 Your approach for doing so will depend on whether you have turned
419 quoting on via the C<quote_char> and C<name_sep> attributes. If you
420 explicitly defined C<quote_char> and C<name_sep> in your
421 C<connect_info> (see L<DBIx::Class::Storage::DBI/"connect_info">) then
422 you are using quoting, otherwise not.
424 If you do not have quoting on, simply include the function in your search
425 specification as you would any column:
427 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
429 With quoting on, or for a more portable solution, use literal SQL values with
432 $rs->search(\[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ]);
435 # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
439 -nest => \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ],
443 # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
445 Note: the C<plain_value> string in the C<< [ plain_value => 1979 ] >> part
446 should be either the same as the name of the column (do this if the type of the
447 return value of the function is the same as the type of the column) or
448 otherwise it's essentially a dummy string currently (use C<plain_value> as a
449 habit). It is used by L<DBIx::Class> to handle special column types.
451 See also L<SQL::Abstract/Literal SQL with placeholders and bind values
454 =head1 JOINS AND PREFETCHING
456 =head2 Using joins and prefetch
458 You can use the C<join> attribute to allow searching on, or sorting your
459 results by, one or more columns in a related table.
461 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
463 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
465 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
467 my $rs = $schema->resultset('CD')->search(
469 'artists.name' => 'Bob Marley'
472 join => 'artists', # join the artist table
477 # SELECT cd.* FROM cd
478 # JOIN artist ON cd.artist = artist.id
479 # WHERE artist.name = 'Bob Marley'
481 In that example both the join, and the condition use the relationship name rather than the table name
482 (see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
484 If required, you can now sort on any column in the related tables by including
485 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
487 my $rs = $schema->resultset('CD')->search(
489 'artists.name' => 'Bob Marley'
493 order_by => [qw/ artists.name /]
498 # SELECT cd.* FROM cd
499 # JOIN artist ON cd.artist = artist.id
500 # WHERE artist.name = 'Bob Marley'
501 # ORDER BY artist.name
503 Note that the C<join> attribute should only be used when you need to search or
504 sort using columns in a related table. Joining related tables when you only
505 need columns from the main table will make performance worse!
507 Now let's say you want to display a list of CDs, each with the name of the
508 artist. The following will work fine:
510 while (my $cd = $rs->next) {
511 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
514 There is a problem however. We have searched both the C<cd> and C<artist> tables
515 in our main query, but we have only returned data from the C<cd> table. To get
516 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
519 SELECT artist.* FROM artist WHERE artist.id = ?
521 A statement like the one above will run for each and every CD returned by our
522 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
525 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
526 This allows you to fetch results from related tables in advance:
528 my $rs = $schema->resultset('CD')->search(
530 'artists.name' => 'Bob Marley'
534 order_by => [qw/ artists.name /],
535 prefetch => 'artists' # return artist data too!
539 # Equivalent SQL (note SELECT from both "cd" and "artist"):
540 # SELECT cd.*, artist.* FROM cd
541 # JOIN artist ON cd.artist = artist.id
542 # WHERE artist.name = 'Bob Marley'
543 # ORDER BY artist.name
545 The code to print the CD list remains the same:
547 while (my $cd = $rs->next) {
548 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
551 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
552 so no additional SQL statements are executed. You now have a much more
555 Also note that C<prefetch> should only be used when you know you will
556 definitely use data from a related table. Pre-fetching related tables when you
557 only need columns from the main table will make performance worse!
559 =head2 Multiple joins
561 In the examples above, the C<join> attribute was a scalar. If you
562 pass an array reference instead, you can join to multiple tables. In
563 this example, we want to limit the search further, using
566 # Relationships defined elsewhere:
567 # CD->belongs_to('artist' => 'Artist');
568 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
569 my $rs = $schema->resultset('CD')->search(
571 'artist.name' => 'Bob Marley'
572 'liner_notes.notes' => { 'like', '%some text%' },
575 join => [qw/ artist liner_notes /],
576 order_by => [qw/ artist.name /],
581 # SELECT cd.*, artist.*, liner_notes.* FROM cd
582 # JOIN artist ON cd.artist = artist.id
583 # JOIN liner_notes ON cd.id = liner_notes.cd
584 # WHERE artist.name = 'Bob Marley'
585 # ORDER BY artist.name
587 =head2 Multi-step joins
589 Sometimes you want to join more than one relationship deep. In this example,
590 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
591 contain a specific string:
593 # Relationships defined elsewhere:
594 # Artist->has_many('cds' => 'CD', 'artist');
595 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
597 my $rs = $schema->resultset('Artist')->search(
599 'liner_notes.notes' => { 'like', '%some text%' },
603 'cds' => 'liner_notes'
609 # SELECT artist.* FROM artist
610 # LEFT JOIN cd ON artist.id = cd.artist
611 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
612 # WHERE liner_notes.notes LIKE '%some text%'
614 Joins can be nested to an arbitrary level. So if we decide later that we
615 want to reduce the number of Artists returned based on who wrote the liner
618 # Relationship defined elsewhere:
619 # LinerNotes->belongs_to('author' => 'Person');
621 my $rs = $schema->resultset('Artist')->search(
623 'liner_notes.notes' => { 'like', '%some text%' },
624 'author.name' => 'A. Writer'
629 'liner_notes' => 'author'
636 # SELECT artist.* FROM artist
637 # LEFT JOIN cd ON artist.id = cd.artist
638 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
639 # LEFT JOIN author ON author.id = liner_notes.author
640 # WHERE liner_notes.notes LIKE '%some text%'
641 # AND author.name = 'A. Writer'
643 =head2 Multi-step and multiple joins
645 With various combinations of array and hash references, you can join
646 tables in any combination you desire. For example, to join Artist to
647 CD and Concert, and join CD to LinerNotes:
649 # Relationships defined elsewhere:
650 # Artist->has_many('concerts' => 'Concert', 'artist');
652 my $rs = $schema->resultset('Artist')->search(
665 # SELECT artist.* FROM artist
666 # LEFT JOIN cd ON artist.id = cd.artist
667 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
668 # LEFT JOIN concert ON artist.id = concert.artist
670 =head2 Multi-step prefetch
672 C<prefetch> can be nested more than one relationship
673 deep using the same syntax as a multi-step join:
675 my $rs = $schema->resultset('Tag')->search(
685 # SELECT tag.*, cd.*, artist.* FROM tag
686 # JOIN cd ON tag.cd = cd.id
687 # JOIN artist ON cd.artist = artist.id
689 Now accessing our C<cd> and C<artist> relationships does not need additional
692 my $tag = $rs->first;
693 print $tag->cd->artist->name;
695 =head1 ROW-LEVEL OPERATIONS
697 =head2 Retrieving a row object's Schema
699 It is possible to get a Schema object from a row object like so:
701 my $schema = $cd->result_source->schema;
702 # use the schema as normal:
703 my $artist_rs = $schema->resultset('Artist');
705 This can be useful when you don't want to pass around a Schema object to every
708 =head2 Getting the value of the primary key for the last database insert
710 AKA getting last_insert_id
712 Thanks to the core component PK::Auto, this is straightforward:
714 my $foo = $rs->create(\%blah);
716 my $id = $foo->id; # foo->my_primary_key_field will also work.
718 If you are not using autoincrementing primary keys, this will probably
719 not work, but then you already know the value of the last primary key anyway.
721 =head2 Stringification
723 Employ the standard stringification technique by using the L<overload>
726 To make an object stringify itself as a single column, use something
727 like this (replace C<name> with the column/method of your choice):
729 use overload '""' => sub { shift->name}, fallback => 1;
731 For more complex stringification, you can use an anonymous subroutine:
733 use overload '""' => sub { $_[0]->name . ", " .
734 $_[0]->address }, fallback => 1;
736 =head3 Stringification Example
738 Suppose we have two tables: C<Product> and C<Category>. The table
741 Product(id, Description, category)
742 Category(id, Description)
744 C<category> is a foreign key into the Category table.
746 If you have a Product object C<$obj> and write something like
750 things will not work as expected.
752 To obtain, for example, the category description, you should add this
753 method to the class defining the Category table:
755 use overload "" => sub {
758 return $self->Description;
761 =head2 Want to know if find_or_create found or created a row?
763 Just use C<find_or_new> instead, then check C<in_storage>:
765 my $obj = $rs->find_or_new({ blah => 'blarg' });
766 unless ($obj->in_storage) {
768 # do whatever else you wanted if it was a new row
771 =head2 Static sub-classing DBIx::Class result classes
773 AKA adding additional relationships/methods/etc. to a model for a
774 specific usage of the (shared) model.
778 package My::App::Schema;
780 use base 'DBIx::Class::Schema';
782 # load subclassed classes from My::App::Schema::Result/ResultSet
783 __PACKAGE__->load_namespaces;
785 # load classes from shared model
787 'My::Shared::Model::Result' => [qw/
794 B<Result-Subclass definition>
796 package My::App::Schema::Result::Baz;
800 use base 'My::Shared::Model::Result::Baz';
802 # WARNING: Make sure you call table() again in your subclass,
803 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
804 # and the class name is not correctly registered as a source
805 __PACKAGE__->table('baz');
807 sub additional_method {
808 return "I'm an additional method only needed by this app";
813 =head2 Dynamic Sub-classing DBIx::Class proxy classes
815 AKA multi-class object inflation from one table
817 L<DBIx::Class> classes are proxy classes, therefore some different
818 techniques need to be employed for more than basic subclassing. In
819 this example we have a single user table that carries a boolean bit
820 for admin. We would like like to give the admin users
821 objects (L<DBIx::Class::Row>) the same methods as a regular user but
822 also special admin only methods. It doesn't make sense to create two
823 separate proxy-class files for this. We would be copying all the user
824 methods into the Admin class. There is a cleaner way to accomplish
827 Overriding the C<inflate_result> method within the User proxy-class
828 gives us the effect we want. This method is called by
829 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
830 grab the object being returned, inspect the values we are looking for,
831 bless it if it's an admin object, and then return it. See the example
838 use base qw/DBIx::Class::Schema/;
840 __PACKAGE__->load_namespaces;
845 B<Proxy-Class definitions>
847 package My::Schema::Result::User;
851 use base qw/DBIx::Class::Core/;
853 ### Define what our admin class is, for ensure_class_loaded()
854 my $admin_class = __PACKAGE__ . '::Admin';
856 __PACKAGE__->table('users');
858 __PACKAGE__->add_columns(qw/user_id email password
859 firstname lastname active
862 __PACKAGE__->set_primary_key('user_id');
866 my $ret = $self->next::method(@_);
867 if( $ret->admin ) {### If this is an admin, rebless for extra functions
868 $self->ensure_class_loaded( $admin_class );
869 bless $ret, $admin_class;
875 print "I am a regular user.\n";
882 package My::Schema::Result::User::Admin;
886 use base qw/My::Schema::Result::User/;
888 # This line is important
889 __PACKAGE__->table('users');
893 print "I am an admin.\n";
899 print "I am doing admin stuff\n";
911 my $user_data = { email => 'someguy@place.com',
915 my $admin_data = { email => 'someadmin@adminplace.com',
919 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
921 $schema->resultset('User')->create( $user_data );
922 $schema->resultset('User')->create( $admin_data );
924 ### Now we search for them
925 my $user = $schema->resultset('User')->single( $user_data );
926 my $admin = $schema->resultset('User')->single( $admin_data );
928 print ref $user, "\n";
929 print ref $admin, "\n";
931 print $user->password , "\n"; # pass1
932 print $admin->password , "\n";# pass2; inherited from User
933 print $user->hello , "\n";# I am a regular user.
934 print $admin->hello, "\n";# I am an admin.
936 ### The statement below will NOT print
937 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
938 ### The statement below will print
939 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
941 Alternatively you can use L<DBIx::Class::DynamicSubclass> that implements
942 exactly the above functionality.
944 =head2 Skip row object creation for faster results
946 DBIx::Class is not built for speed, it's built for convenience and
947 ease of use, but sometimes you just need to get the data, and skip the
950 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
952 my $rs = $schema->resultset('CD');
954 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
956 my $hash_ref = $rs->find(1);
960 Beware, changing the Result class using
961 L<DBIx::Class::ResultSet/result_class> will replace any existing class
962 completely including any special components loaded using
963 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
965 =head2 Get raw data for blindingly fast results
967 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
968 above is not fast enough for you, you can use a DBIx::Class to return values
969 exactly as they come out of the database with none of the convenience methods
972 This is used like so:
974 my $cursor = $rs->cursor
975 while (my @vals = $cursor->next) {
976 # use $val[0..n] here
979 You will need to map the array offsets to particular columns (you can
980 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
982 =head1 RESULTSET OPERATIONS
984 =head2 Getting Schema from a ResultSet
986 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
988 $rs->result_source->schema
990 =head2 Getting Columns Of Data
994 If you want to find the sum of a particular column there are several
995 ways, the obvious one is to use search:
997 my $rs = $schema->resultset('Items')->search(
1000 select => [ { sum => 'Cost' } ],
1001 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
1004 my $tc = $rs->first->get_column('total_cost');
1006 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
1007 returned when you ask the C<ResultSet> for a column using
1010 my $cost = $schema->resultset('Items')->get_column('Cost');
1011 my $tc = $cost->sum;
1013 With this you can also do:
1015 my $minvalue = $cost->min;
1016 my $maxvalue = $cost->max;
1018 Or just iterate through the values of this column only:
1020 while ( my $c = $cost->next ) {
1024 foreach my $c ($cost->all) {
1028 C<ResultSetColumn> only has a limited number of built-in functions. If
1029 you need one that it doesn't have, then you can use the C<func> method
1032 my $avg = $cost->func('AVERAGE');
1034 This will cause the following SQL statement to be run:
1036 SELECT AVERAGE(Cost) FROM Items me
1038 Which will of course only work if your database supports this function.
1039 See L<DBIx::Class::ResultSetColumn> for more documentation.
1041 =head2 Creating a result set from a set of rows
1043 Sometimes you have a (set of) row objects that you want to put into a
1044 resultset without the need to hit the DB again. You can do that by using the
1045 L<set_cache|DBIx::Class::Resultset/set_cache> method:
1047 my @uploadable_groups;
1048 while (my $group = $groups->next) {
1049 if ($group->can_upload($self)) {
1050 push @uploadable_groups, $group;
1053 my $new_rs = $self->result_source->resultset;
1054 $new_rs->set_cache(\@uploadable_groups);
1058 =head1 USING RELATIONSHIPS
1060 =head2 Create a new row in a related table
1062 my $author = $book->create_related('author', { name => 'Fred'});
1064 =head2 Search in a related table
1066 Only searches for books named 'Titanic' by the author in $author.
1068 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1070 =head2 Delete data in a related table
1072 Deletes only the book named Titanic by the author in $author.
1074 $author->delete_related('books', { name => 'Titanic' });
1076 =head2 Ordering a relationship result set
1078 If you always want a relation to be ordered, you can specify this when you
1079 create the relationship.
1081 To order C<< $book->pages >> by descending page_number, create the relation
1084 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
1086 =head2 Filtering a relationship result set
1088 If you want to get a filtered result set, you can just add add to $attr as follows:
1090 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1092 =head2 Many-to-many relationships
1094 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1097 use base 'DBIx::Class::Core';
1098 __PACKAGE__->table('user');
1099 __PACKAGE__->add_columns(qw/id name/);
1100 __PACKAGE__->set_primary_key('id');
1101 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1102 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1104 package My::UserAddress;
1105 use base 'DBIx::Class::Core';
1106 __PACKAGE__->table('user_address');
1107 __PACKAGE__->add_columns(qw/user address/);
1108 __PACKAGE__->set_primary_key(qw/user address/);
1109 __PACKAGE__->belongs_to('user' => 'My::User');
1110 __PACKAGE__->belongs_to('address' => 'My::Address');
1112 package My::Address;
1113 use base 'DBIx::Class::Core';
1114 __PACKAGE__->table('address');
1115 __PACKAGE__->add_columns(qw/id street town area_code country/);
1116 __PACKAGE__->set_primary_key('id');
1117 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1118 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1120 $rs = $user->addresses(); # get all addresses for a user
1121 $rs = $address->users(); # get all users for an address
1123 my $address = $user->add_to_addresses( # returns a My::Address instance,
1124 # NOT a My::UserAddress instance!
1126 country => 'United Kingdom',
1133 =head2 Relationships across DB schemas
1135 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1136 is easy as long as the schemas themselves are all accessible via the same DBI
1137 connection. In most cases, this means that they are on the same database host
1138 as each other and your connecting database user has the proper permissions to them.
1140 To accomplish this one only needs to specify the DB schema name in the table
1141 declaration, like so...
1143 package MyDatabase::Main::Artist;
1144 use base qw/DBIx::Class::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 =head2 Transactions with txn_do
1228 As of version 0.04001, there is improved transaction support in
1229 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1230 example of the recommended way to use it:
1232 my $genus = $schema->resultset('Genus')->find(12);
1234 my $coderef2 = sub {
1239 my $coderef1 = sub {
1240 $genus->add_to_species({ name => 'troglodyte' });
1243 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1244 return $genus->species;
1250 $rs = $schema->txn_do($coderef1);
1252 # Transaction failed
1253 die "the sky is falling!" #
1254 if ($_ =~ /Rollback failed/); # Rollback failed
1256 deal_with_failed_transaction();
1259 Note: by default C<txn_do> will re-run the coderef one more time if an
1260 error occurs due to client disconnection (e.g. the server is bounced).
1261 You need to make sure that your coderef can be invoked multiple times
1262 without terrible side effects.
1264 Nested transactions will work as expected. That is, only the outermost
1265 transaction will actually issue a commit to the $dbh, and a rollback
1266 at any level of any transaction will cause the entire nested
1267 transaction to fail.
1269 =head2 Nested transactions and auto-savepoints
1271 If savepoints are supported by your RDBMS, it is possible to achieve true
1272 nested transactions with minimal effort. To enable auto-savepoints via nested
1273 transactions, supply the C<< auto_savepoint = 1 >> connection attribute.
1275 Here is an example of true nested transactions. In the example, we start a big
1276 task which will create several rows. Generation of data for each row is a
1277 fragile operation and might fail. If we fail creating something, depending on
1278 the type of failure, we want to abort the whole task, or only skip the failed
1281 my $schema = MySchema->connect("dbi:Pg:dbname=my_db");
1283 # Start a transaction. Every database change from here on will only be
1284 # committed into the database if the try block succeeds.
1288 $schema->txn_do(sub {
1291 my $job = $schema->resultset('Job')->create({ name=> 'big job' });
1292 # SQL: INSERT INTO job ( name) VALUES ( 'big job' );
1296 # Start a nested transaction, which in fact sets a savepoint.
1298 $schema->txn_do(sub {
1299 # SQL: SAVEPOINT savepoint_0;
1301 my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
1302 # SQL: INSERT INTO thing ( job) VALUES ( 1 );
1305 # This will generate an error, thus setting $@
1307 $thing->update({force_fail=>'foo'});
1308 # SQL: UPDATE thing SET force_fail = 'foo'
1309 # WHERE ( id = 42 );
1313 # SQL: ROLLBACK TO SAVEPOINT savepoint_0;
1315 # There was an error while creating a $thing. Depending on the error
1316 # we want to abort the whole transaction, or only rollback the
1317 # changes related to the creation of this $thing
1319 # Abort the whole job
1320 if ($_ =~ /horrible_problem/) {
1321 print "something horrible happend, aborting job!";
1322 die $_; # rethrow error
1325 # Ignore this $thing, report the error, and continue with the
1327 print "Cannot create thing: $_";
1329 # There was no error, so save all changes since the last
1332 # SQL: RELEASE SAVEPOINT savepoint_0;
1340 # There was an error while handling the $job. Rollback all changes
1341 # since the transaction started, including the already committed
1342 # ('released') savepoints. There will be neither a new $job nor any
1343 # $thing entry in the database.
1347 print "ERROR: $exception\n";
1350 # There was no error while handling the $job. Commit all changes.
1351 # Only now other connections can see the newly created $job and
1359 In this example it might be hard to see where the rollbacks, releases and
1360 commits are happening, but it works just the same as for plain L<<txn_do>>: If
1361 the C<try>-block around C<txn_do> fails, a rollback is issued. If the C<try>
1362 succeeds, the transaction is committed (or the savepoint released).
1364 While you can get more fine-grained control using C<svp_begin>, C<svp_release>
1365 and C<svp_rollback>, it is strongly recommended to use C<txn_do> with coderefs.
1367 =head2 Simple Transactions with DBIx::Class::Storage::TxnScopeGuard
1369 An easy way to use transactions is with
1370 L<DBIx::Class::Storage::TxnScopeGuard>. See L</Automatically creating
1371 related objects> for an example.
1373 Note that unlike txn_do, TxnScopeGuard will only make sure the connection is
1374 alive when issuing the C<BEGIN> statement. It will not (and really can not)
1375 retry if the server goes away mid-operations, unlike C<txn_do>.
1379 =head2 Creating Schemas From An Existing Database
1381 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1382 L<DBIx::Class::Schema> and associated sources by examining the database.
1384 The recommend way of achieving this is to use the
1385 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1387 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1388 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1390 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1391 source definitions for all the tables found in the C<foo> database.
1393 =head2 Creating DDL SQL
1395 The following functionality requires you to have L<SQL::Translator>
1396 (also known as "SQL Fairy") installed.
1398 To create a set of database-specific .sql files for the above schema:
1400 my $schema = My::Schema->connect($dsn);
1401 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1406 By default this will create schema files in the current directory, for
1407 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1409 To create a new database using the schema:
1411 my $schema = My::Schema->connect($dsn);
1412 $schema->deploy({ add_drop_table => 1});
1414 To import created .sql files using the mysql client:
1416 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1418 To create C<ALTER TABLE> conversion scripts to update a database to a
1419 newer version of your schema at a later point, first set a new
1420 C<$VERSION> in your Schema file, then:
1422 my $schema = My::Schema->connect($dsn);
1423 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1429 This will produce new database-specific .sql files for the new version
1430 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1431 requires that the files for 0.1 as created above are available in the
1432 given directory to diff against.
1434 =head2 Select from dual
1436 Dummy tables are needed by some databases to allow calling functions
1437 or expressions that aren't based on table content, for examples of how
1438 this applies to various database types, see:
1439 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1441 Note: If you're using Oracles dual table don't B<ever> do anything
1442 other than a select, if you CRUD on your dual table you *will* break
1445 Make a table class as you would for any other table
1447 package MyAppDB::Dual;
1450 use base 'DBIx::Class::Core';
1451 __PACKAGE__->table("Dual");
1452 __PACKAGE__->add_columns(
1454 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1457 Once you've loaded your table class select from it using C<select>
1458 and C<as> instead of C<columns>
1460 my $rs = $schema->resultset('Dual')->search(undef,
1461 { select => [ 'sydate' ],
1466 All you have to do now is be careful how you access your resultset, the below
1467 will not work because there is no column called 'now' in the Dual table class
1469 while (my $dual = $rs->next) {
1470 print $dual->now."\n";
1472 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1474 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1475 your Dual class for whatever you wanted to select from dual, but that's just
1476 silly, instead use C<get_column>
1478 while (my $dual = $rs->next) {
1479 print $dual->get_column('now')."\n";
1484 my $cursor = $rs->cursor;
1485 while (my @vals = $cursor->next) {
1486 print $vals[0]."\n";
1489 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1490 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1491 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1492 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1493 L<SQL::Translator> to not create table dual:
1496 add_drop_table => 1,
1497 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1499 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1501 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1503 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1504 while ( my $dual = $rs->next ) {
1505 print $dual->{now}."\n";
1508 Here are some example C<select> conditions to illustrate the different syntax
1509 you could use for doing stuff like
1510 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1512 # get a sequence value
1513 select => [ 'A_SEQ.nextval' ],
1515 # get create table sql
1516 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1518 # get a random num between 0 and 100
1519 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1522 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1525 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1527 # which day of the week were you born on?
1528 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1530 # select 16 rows from dual
1531 select => [ "'hello'" ],
1533 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1537 =head2 Adding Indexes And Functions To Your SQL
1539 Often you will want indexes on columns on your table to speed up searching. To
1540 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1541 class (refer to the advanced
1542 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1543 to share a hook between multiple sources):
1545 package My::Schema::Result::Artist;
1547 __PACKAGE__->table('artist');
1548 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1550 sub sqlt_deploy_hook {
1551 my ($self, $sqlt_table) = @_;
1553 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1558 Sometimes you might want to change the index depending on the type of the
1559 database for which SQL is being generated:
1561 my ($db_type = $sqlt_table->schema->translator->producer_type)
1562 =~ s/^SQL::Translator::Producer:://;
1564 You can also add hooks to the schema level to stop certain tables being
1571 sub sqlt_deploy_hook {
1572 my ($self, $sqlt_schema) = @_;
1574 $sqlt_schema->drop_table('table_name');
1577 You could also add views, procedures or triggers to the output using
1578 L<SQL::Translator::Schema/add_view>,
1579 L<SQL::Translator::Schema/add_procedure> or
1580 L<SQL::Translator::Schema/add_trigger>.
1583 =head2 Schema versioning
1585 The following example shows simplistically how you might use DBIx::Class to
1586 deploy versioned schemas to your customers. The basic process is as follows:
1592 Create a DBIx::Class schema
1604 Modify schema to change functionality
1608 Deploy update to customers
1612 B<Create a DBIx::Class schema>
1614 This can either be done manually, or generated from an existing database as
1615 described under L</Creating Schemas From An Existing Database>
1619 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1621 B<Deploy to customers>
1623 There are several ways you could deploy your schema. These are probably
1624 beyond the scope of this recipe, but might include:
1630 Require customer to apply manually using their RDBMS.
1634 Package along with your app, making database dump/schema update/tests
1635 all part of your install.
1639 B<Modify the schema to change functionality>
1641 As your application evolves, it may be necessary to modify your schema
1642 to change functionality. Once the changes are made to your schema in
1643 DBIx::Class, export the modified schema and the conversion scripts as
1644 in L</Creating DDL SQL>.
1646 B<Deploy update to customers>
1648 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1649 Schema class. This will add a new table to your database called
1650 C<dbix_class_schema_vesion> which will keep track of which version is installed
1651 and warn if the user tries to run a newer schema version than the
1652 database thinks it has.
1654 Alternatively, you can send the conversion SQL scripts to your
1657 =head2 Setting quoting for the generated SQL
1659 If the database contains column names with spaces and/or reserved words, they
1660 need to be quoted in the SQL queries. This is done using:
1662 $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
1663 $schema->storage->sql_maker->name_sep('.');
1665 The first sets the quote characters. Either a pair of matching
1666 brackets, or a C<"> or C<'>:
1668 $schema->storage->sql_maker->quote_char('"');
1670 Check the documentation of your database for the correct quote
1671 characters to use. C<name_sep> needs to be set to allow the SQL
1672 generator to put the quotes the correct place.
1674 In most cases you should set these as part of the arguments passed to
1675 L<DBIx::Class::Schema/connect>:
1677 my $schema = My::Schema->connect(
1687 In some cases, quoting will be required for all users of a schema. To enforce
1688 this, you can also overload the C<connection> method for your schema class:
1692 my $rv = $self->next::method( @_ );
1693 $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
1694 $rv->storage->sql_maker->name_sep('.');
1698 =head2 Setting limit dialect for SQL::Abstract::Limit
1700 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1701 the remote SQL server by looking at the database handle. This is a
1702 common problem when using the DBD::JDBC, since the DBD-driver only
1703 know that in has a Java-driver available, not which JDBC driver the
1704 Java component has loaded. This specifically sets the limit_dialect
1705 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1708 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1710 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1711 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1713 The limit dialect can also be set at connect time by specifying a
1714 C<limit_dialect> key in the final hash as shown above.
1716 =head2 Working with PostgreSQL array types
1718 You can also assign values to PostgreSQL array columns by passing array
1719 references in the C<\%columns> (C<\%vals>) hashref of the
1720 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1723 $resultset->create({
1724 numbers => [1, 2, 3]
1729 numbers => [1, 2, 3]
1736 In conditions (e.g. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1737 methods) you cannot directly use array references (since this is interpreted as
1738 a list of values to be C<OR>ed), but you can use the following syntax to force
1739 passing them as bind values:
1743 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1747 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1748 placeholders and bind values (subqueries)> for more explanation. Note that
1749 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1750 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1751 arrayrefs together with the column name, like this: C<< [column_name => value]
1754 =head2 Using Unicode
1756 When using unicode character data there are two alternatives -
1757 either your database supports unicode characters (including setting
1758 the utf8 flag on the returned string), or you need to encode/decode
1759 data appropriately each time a string field is inserted into or
1760 retrieved from the database. It is better to avoid
1761 encoding/decoding data and to use your database's own unicode
1762 capabilities if at all possible.
1764 The L<DBIx::Class::UTF8Columns> component handles storing selected
1765 unicode columns in a database that does not directly support
1766 unicode. If used with a database that does correctly handle unicode
1767 then strange and unexpected data corrupt B<will> occur.
1769 The Catalyst Wiki Unicode page at
1770 L<http://wiki.catalystframework.org/wiki/tutorialsandhowtos/using_unicode>
1771 has additional information on the use of Unicode with Catalyst and
1774 The following databases do correctly handle unicode data:-
1778 MySQL supports unicode, and will correctly flag utf8 data from the
1779 database if the C<mysql_enable_utf8> is set in the connect options.
1781 my $schema = My::Schema->connection('dbi:mysql:dbname=test',
1783 { mysql_enable_utf8 => 1} );
1786 When set, a data retrieved from a textual column type (char,
1787 varchar, etc) will have the UTF-8 flag turned on if necessary. This
1788 enables character semantics on that string. You will also need to
1789 ensure that your database / table / column is configured to use
1790 UTF8. See Chapter 10 of the mysql manual for details.
1792 See L<DBD::mysql> for further details.
1796 Information about Oracle support for unicode can be found in
1797 L<DBD::Oracle/Unicode>.
1801 PostgreSQL supports unicode if the character set is correctly set
1802 at database creation time. Additionally the C<pg_enable_utf8>
1803 should be set to ensure unicode data is correctly marked.
1805 my $schema = My::Schema->connection('dbi:Pg:dbname=test',
1807 { pg_enable_utf8 => 1} );
1809 Further information can be found in L<DBD::Pg>.
1813 SQLite version 3 and above natively use unicode internally. To
1814 correctly mark unicode strings taken from the database, the
1815 C<sqlite_unicode> flag should be set at connect time (in versions
1816 of L<DBD::SQLite> prior to 1.27 this attribute was named
1819 my $schema = My::Schema->connection('dbi:SQLite:/tmp/test.db',
1821 { sqlite_unicode => 1} );
1823 =head1 BOOTSTRAPPING/MIGRATING
1825 =head2 Easy migration from class-based to schema-based setup
1827 You want to start using the schema-based approach to L<DBIx::Class>
1828 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1829 of existing classes that you don't want to move by hand. Try this nifty script
1833 use SQL::Translator;
1835 my $schema = MyDB->schema_instance;
1837 my $translator = SQL::Translator->new(
1838 debug => $debug || 0,
1839 trace => $trace || 0,
1840 no_comments => $no_comments || 0,
1841 show_warnings => $show_warnings || 0,
1842 add_drop_table => $add_drop_table || 0,
1843 validate => $validate || 0,
1845 'DBIx::Schema' => $schema,
1848 'prefix' => 'My::Schema',
1852 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1853 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1855 my $output = $translator->translate(@args) or die
1856 "Error: " . $translator->error;
1860 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1861 namespace, which is currently left as an exercise for the reader.
1863 =head1 OVERLOADING METHODS
1865 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1866 method calls, useful for things like default values and triggers. You have to
1867 use calls to C<next::method> to overload methods. More information on using
1868 L<Class::C3> with L<DBIx::Class> can be found in
1869 L<DBIx::Class::Manual::Component>.
1871 =head2 Setting default values for a row
1873 It's as simple as overriding the C<new> method. Note the use of
1877 my ( $class, $attrs ) = @_;
1879 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1881 my $new = $class->next::method($attrs);
1886 For more information about C<next::method>, look in the L<Class::C3>
1887 documentation. See also L<DBIx::Class::Manual::Component> for more
1888 ways to write your own base classes to do this.
1890 People looking for ways to do "triggers" with DBIx::Class are probably
1891 just looking for this.
1893 =head2 Changing one field whenever another changes
1895 For example, say that you have three columns, C<id>, C<number>, and
1896 C<squared>. You would like to make changes to C<number> and have
1897 C<squared> be automagically set to the value of C<number> squared.
1898 You can accomplish this by overriding C<store_column>:
1901 my ( $self, $name, $value ) = @_;
1902 if ($name eq 'number') {
1903 $self->squared($value * $value);
1905 $self->next::method($name, $value);
1908 Note that the hard work is done by the call to C<next::method>, which
1909 redispatches your call to store_column in the superclass(es).
1911 =head2 Automatically creating related objects
1913 You might have a class C<Artist> which has many C<CD>s. Further, you
1914 want to create a C<CD> object every time you insert an C<Artist> object.
1915 You can accomplish this by overriding C<insert> on your objects:
1918 my ( $self, @args ) = @_;
1919 $self->next::method(@args);
1920 $self->create_related ('cds', \%initial_cd_data );
1924 If you want to wrap the two inserts in a transaction (for consistency,
1925 an excellent idea), you can use the awesome
1926 L<DBIx::Class::Storage::TxnScopeGuard>:
1929 my ( $self, @args ) = @_;
1931 my $guard = $self->result_source->schema->txn_scope_guard;
1933 $self->next::method(@args);
1934 $self->create_related ('cds', \%initial_cd_data );
1942 =head2 Wrapping/overloading a column accessor
1946 Say you have a table "Camera" and want to associate a description
1947 with each camera. For most cameras, you'll be able to generate the description from
1948 the other columns. However, in a few special cases you may want to associate a
1949 custom description with a camera.
1953 In your database schema, define a description field in the "Camera" table that
1954 can contain text and null values.
1956 In DBIC, we'll overload the column accessor to provide a sane default if no
1957 custom description is defined. The accessor will either return or generate the
1958 description, depending on whether the field is null or not.
1960 First, in your "Camera" schema class, define the description field as follows:
1962 __PACKAGE__->add_columns(description => { accessor => '_description' });
1964 Next, we'll define the accessor-wrapper subroutine:
1969 # If there is an update to the column, we'll let the original accessor
1971 return $self->_description(@_) if @_;
1973 # Fetch the column value.
1974 my $description = $self->_description;
1976 # If there's something in the description field, then just return that.
1977 return $description if defined $description && length $descripton;
1979 # Otherwise, generate a description.
1980 return $self->generate_description;
1983 =head1 DEBUGGING AND PROFILING
1985 =head2 DBIx::Class objects with Data::Dumper
1987 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1988 be hard to find the pertinent data in all the data it can generate.
1989 Specifically, if one naively tries to use it like so,
1993 my $cd = $schema->resultset('CD')->find(1);
1996 several pages worth of data from the CD object's schema and result source will
1997 be dumped to the screen. Since usually one is only interested in a few column
1998 values of the object, this is not very helpful.
2000 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
2001 it. Simply define a hook that L<Data::Dumper> will call on the object before
2002 dumping it. For example,
2009 result_source => undef,
2017 local $Data::Dumper::Freezer = '_dumper_hook';
2019 my $cd = $schema->resultset('CD')->find(1);
2021 # dumps $cd without its ResultSource
2023 If the structure of your schema is such that there is a common base class for
2024 all your table classes, simply put a method similar to C<_dumper_hook> in the
2025 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
2026 will automagically clean up your data before printing it. See
2027 L<Data::Dumper/EXAMPLES> for more information.
2031 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
2032 executed as well as notifications of query completion and transaction
2033 begin/commit. If you'd like to profile the SQL you can subclass the
2034 L<DBIx::Class::Storage::Statistics> class and write your own profiling
2037 package My::Profiler;
2040 use base 'DBIx::Class::Storage::Statistics';
2042 use Time::HiRes qw(time);
2051 $self->print("Executing $sql: ".join(', ', @params)."\n");
2060 my $elapsed = sprintf("%0.4f", time() - $start);
2061 $self->print("Execution took $elapsed seconds.\n");
2067 You can then install that class as the debugging object:
2069 __PACKAGE__->storage->debugobj(new My::Profiler());
2070 __PACKAGE__->storage->debug(1);
2072 A more complicated example might involve storing each execution of SQL in an
2080 my $elapsed = time() - $start;
2081 push(@{ $calls{$sql} }, {
2087 You could then create average, high and low execution times for an SQL
2088 statement and dig down to see if certain parameters cause aberrant behavior.
2089 You might want to check out L<DBIx::Class::QueryLog> as well.
2091 =head1 IMPROVING PERFORMANCE
2097 Install L<Class::XSAccessor> to speed up L<Class::Accessor::Grouped>.
2101 On Perl 5.8 install L<Class::C3::XS>.
2105 L<prefetch|DBIx::Class::ResultSet/prefetch> relationships, where possible. See
2106 L</Using joins and prefetch>.
2110 Use L<populate|DBIx::Class::ResultSet/populate> in void context to insert data
2111 when you don't need the resulting L<DBIx::Class::Row> objects, if possible, but
2114 When inserting many rows, for best results, populate a large number of rows at a
2115 time, but not so large that the table is locked for an unacceptably long time.
2117 If using L<create|DBIx::Class::ResultSet/create> instead, use a transaction and
2118 commit every C<X> rows; where C<X> gives you the best performance without
2119 locking the table for too long.
2123 When selecting many rows, if you don't need full-blown L<DBIx::Class::Row>
2124 objects, consider using L<DBIx::Class::ResultClass::HashRefInflator>.
2128 See also L</STARTUP SPEED> and L</MEMORY USAGE> in this document.
2132 =head1 STARTUP SPEED
2134 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
2135 as the ORM loads all the relevant classes. This section examines
2136 techniques for reducing the startup delay.
2138 These tips are are listed in order of decreasing effectiveness - so the
2139 first tip, if applicable, should have the greatest effect on your
2142 =head2 Statically Define Your Schema
2145 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
2146 classes dynamically based on the database schema then there will be a
2147 significant startup delay.
2149 For production use a statically defined schema (which can be generated
2150 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
2151 the database schema once - see
2152 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
2153 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
2154 details on creating static schemas from a database).
2156 =head2 Move Common Startup into a Base Class
2158 Typically L<DBIx::Class> result classes start off with
2160 use base qw/DBIx::Class::Core/;
2161 __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2163 If this preamble is moved into a common base class:-
2167 use base qw/DBIx::Class::Core/;
2168 __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2171 and each result class then uses this as a base:-
2173 use base qw/MyDBICbase/;
2175 then the load_components is only performed once, which can result in a
2176 considerable startup speedup for schemas with many classes.
2178 =head2 Explicitly List Schema Result Classes
2180 The schema class will normally contain
2182 __PACKAGE__->load_classes();
2184 to load the result classes. This will use L<Module::Find|Module::Find>
2185 to find and load the appropriate modules. Explicitly defining the
2186 classes you wish to load will remove the overhead of
2187 L<Module::Find|Module::Find> and the related directory operations:
2189 __PACKAGE__->load_classes(qw/ CD Artist Track /);
2191 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
2192 syntax to load the appropriate classes there is not a direct alternative
2193 avoiding L<Module::Find|Module::Find>.
2197 =head2 Cached statements
2199 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
2200 This is normally a good idea, but if too many statements are cached, the database may use too much
2201 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
2202 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
2204 # print all currently cached prepared statements
2205 print for keys %{$schema->storage->dbh->{CachedKids}};
2206 # get a count of currently cached prepared statements
2207 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
2209 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
2212 my $kids = $schema->storage->dbh->{CachedKids};
2213 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
2215 But what you probably want is to expire unused statements and not those that are used frequently.
2216 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
2220 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
2221 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },