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 To use your resultset, first tell DBIx::Class to create an instance of it
394 for you, in your My::DBIC::Schema::CD class:
396 # class definition as normal
397 use base 'DBIx::Class::Core';
398 __PACKAGE__->table('cd');
400 # tell DBIC to use the custom ResultSet class
401 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
403 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
405 Then call your new method in your code:
407 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
409 =head2 Using SQL functions on the left hand side of a comparison
411 Using SQL functions on the left hand side of a comparison is generally not a
412 good idea since it requires a scan of the entire table. (Unless your RDBMS
413 supports indexes on expressions - including return values of functions -, and
414 you create an index on the return value of the function in question.) However,
415 it can be accomplished with C<DBIx::Class> when necessary.
417 If you do not have quoting on, simply include the function in your search
418 specification as you would any column:
420 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
422 With quoting on, or for a more portable solution, use literal SQL values with
425 $rs->search(\[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ]);
428 # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
432 -nest => \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ],
436 # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
438 Note: the C<plain_value> string in the C<< [ plain_value => 1979 ] >> part
439 should be either the same as the name of the column (do this if the type of the
440 return value of the function is the same as the type of the column) or
441 otherwise it's essentially a dummy string currently (use C<plain_value> as a
442 habit). It is used by L<DBIx::Class> to handle special column types.
444 See also L<SQL::Abstract/Literal SQL with placeholders and bind values
447 =head1 JOINS AND PREFETCHING
449 =head2 Using joins and prefetch
451 You can use the C<join> attribute to allow searching on, or sorting your
452 results by, one or more columns in a related table.
454 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
456 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
458 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
460 my $rs = $schema->resultset('CD')->search(
462 'artists.name' => 'Bob Marley'
465 join => 'artists', # join the artist table
470 # SELECT cd.* FROM cd
471 # JOIN artist ON cd.artist = artist.id
472 # WHERE artist.name = 'Bob Marley'
474 In that example both the join, and the condition use the relationship name rather than the table name
475 (see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
477 If required, you can now sort on any column in the related tables by including
478 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
480 my $rs = $schema->resultset('CD')->search(
482 'artists.name' => 'Bob Marley'
486 order_by => [qw/ artists.name /]
491 # SELECT cd.* FROM cd
492 # JOIN artist ON cd.artist = artist.id
493 # WHERE artist.name = 'Bob Marley'
494 # ORDER BY artist.name
496 Note that the C<join> attribute should only be used when you need to search or
497 sort using columns in a related table. Joining related tables when you only
498 need columns from the main table will make performance worse!
500 Now let's say you want to display a list of CDs, each with the name of the
501 artist. The following will work fine:
503 while (my $cd = $rs->next) {
504 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
507 There is a problem however. We have searched both the C<cd> and C<artist> tables
508 in our main query, but we have only returned data from the C<cd> table. To get
509 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
512 SELECT artist.* FROM artist WHERE artist.id = ?
514 A statement like the one above will run for each and every CD returned by our
515 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
518 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
519 This allows you to fetch results from related tables in advance:
521 my $rs = $schema->resultset('CD')->search(
523 'artists.name' => 'Bob Marley'
527 order_by => [qw/ artists.name /],
528 prefetch => 'artists' # return artist data too!
532 # Equivalent SQL (note SELECT from both "cd" and "artist"):
533 # SELECT cd.*, artist.* FROM cd
534 # JOIN artist ON cd.artist = artist.id
535 # WHERE artist.name = 'Bob Marley'
536 # ORDER BY artist.name
538 The code to print the CD list remains the same:
540 while (my $cd = $rs->next) {
541 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
544 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
545 so no additional SQL statements are executed. You now have a much more
548 Also note that C<prefetch> should only be used when you know you will
549 definitely use data from a related table. Pre-fetching related tables when you
550 only need columns from the main table will make performance worse!
552 =head2 Multiple joins
554 In the examples above, the C<join> attribute was a scalar. If you
555 pass an array reference instead, you can join to multiple tables. In
556 this example, we want to limit the search further, using
559 # Relationships defined elsewhere:
560 # CD->belongs_to('artist' => 'Artist');
561 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
562 my $rs = $schema->resultset('CD')->search(
564 'artist.name' => 'Bob Marley'
565 'liner_notes.notes' => { 'like', '%some text%' },
568 join => [qw/ artist liner_notes /],
569 order_by => [qw/ artist.name /],
574 # SELECT cd.*, artist.*, liner_notes.* FROM cd
575 # JOIN artist ON cd.artist = artist.id
576 # JOIN liner_notes ON cd.id = liner_notes.cd
577 # WHERE artist.name = 'Bob Marley'
578 # ORDER BY artist.name
580 =head2 Multi-step joins
582 Sometimes you want to join more than one relationship deep. In this example,
583 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
584 contain a specific string:
586 # Relationships defined elsewhere:
587 # Artist->has_many('cds' => 'CD', 'artist');
588 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
590 my $rs = $schema->resultset('Artist')->search(
592 'liner_notes.notes' => { 'like', '%some text%' },
596 'cds' => 'liner_notes'
602 # SELECT artist.* FROM artist
603 # LEFT JOIN cd ON artist.id = cd.artist
604 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
605 # WHERE liner_notes.notes LIKE '%some text%'
607 Joins can be nested to an arbitrary level. So if we decide later that we
608 want to reduce the number of Artists returned based on who wrote the liner
611 # Relationship defined elsewhere:
612 # LinerNotes->belongs_to('author' => 'Person');
614 my $rs = $schema->resultset('Artist')->search(
616 'liner_notes.notes' => { 'like', '%some text%' },
617 'author.name' => 'A. Writer'
622 'liner_notes' => 'author'
629 # SELECT artist.* FROM artist
630 # LEFT JOIN cd ON artist.id = cd.artist
631 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
632 # LEFT JOIN author ON author.id = liner_notes.author
633 # WHERE liner_notes.notes LIKE '%some text%'
634 # AND author.name = 'A. Writer'
636 =head2 Multi-step and multiple joins
638 With various combinations of array and hash references, you can join
639 tables in any combination you desire. For example, to join Artist to
640 CD and Concert, and join CD to LinerNotes:
642 # Relationships defined elsewhere:
643 # Artist->has_many('concerts' => 'Concert', 'artist');
645 my $rs = $schema->resultset('Artist')->search(
658 # SELECT artist.* FROM artist
659 # LEFT JOIN cd ON artist.id = cd.artist
660 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
661 # LEFT JOIN concert ON artist.id = concert.artist
663 =head2 Multi-step prefetch
665 C<prefetch> can be nested more than one relationship
666 deep using the same syntax as a multi-step join:
668 my $rs = $schema->resultset('Tag')->search(
678 # SELECT tag.*, cd.*, artist.* FROM tag
679 # JOIN cd ON tag.cd = cd.id
680 # JOIN artist ON cd.artist = artist.id
682 Now accessing our C<cd> and C<artist> relationships does not need additional
685 my $tag = $rs->first;
686 print $tag->cd->artist->name;
688 =head1 ROW-LEVEL OPERATIONS
690 =head2 Retrieving a row object's Schema
692 It is possible to get a Schema object from a row object like so:
694 my $schema = $cd->result_source->schema;
695 # use the schema as normal:
696 my $artist_rs = $schema->resultset('Artist');
698 This can be useful when you don't want to pass around a Schema object to every
701 =head2 Getting the value of the primary key for the last database insert
703 AKA getting last_insert_id
705 Thanks to the core component PK::Auto, this is straightforward:
707 my $foo = $rs->create(\%blah);
709 my $id = $foo->id; # foo->my_primary_key_field will also work.
711 If you are not using autoincrementing primary keys, this will probably
712 not work, but then you already know the value of the last primary key anyway.
714 =head2 Stringification
716 Employ the standard stringification technique by using the L<overload>
719 To make an object stringify itself as a single column, use something
720 like this (replace C<name> with the column/method of your choice):
722 use overload '""' => sub { shift->name}, fallback => 1;
724 For more complex stringification, you can use an anonymous subroutine:
726 use overload '""' => sub { $_[0]->name . ", " .
727 $_[0]->address }, fallback => 1;
729 =head3 Stringification Example
731 Suppose we have two tables: C<Product> and C<Category>. The table
734 Product(id, Description, category)
735 Category(id, Description)
737 C<category> is a foreign key into the Category table.
739 If you have a Product object C<$obj> and write something like
743 things will not work as expected.
745 To obtain, for example, the category description, you should add this
746 method to the class defining the Category table:
748 use overload "" => sub {
751 return $self->Description;
754 =head2 Want to know if find_or_create found or created a row?
756 Just use C<find_or_new> instead, then check C<in_storage>:
758 my $obj = $rs->find_or_new({ blah => 'blarg' });
759 unless ($obj->in_storage) {
761 # do whatever else you wanted if it was a new row
764 =head2 Static sub-classing DBIx::Class result classes
766 AKA adding additional relationships/methods/etc. to a model for a
767 specific usage of the (shared) model.
771 package My::App::Schema;
773 use base DBIx::Class::Schema;
775 # load subclassed classes from My::App::Schema::Result/ResultSet
776 __PACKAGE__->load_namespaces;
778 # load classes from shared model
780 'My::Shared::Model::Result' => [qw/
787 B<Result-Subclass definition>
789 package My::App::Schema::Result::Baz;
793 use base My::Shared::Model::Result::Baz;
795 # WARNING: Make sure you call table() again in your subclass,
796 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
797 # and the class name is not correctly registered as a source
798 __PACKAGE__->table('baz');
800 sub additional_method {
801 return "I'm an additional method only needed by this app";
806 =head2 Dynamic Sub-classing DBIx::Class proxy classes
808 AKA multi-class object inflation from one table
810 L<DBIx::Class> classes are proxy classes, therefore some different
811 techniques need to be employed for more than basic subclassing. In
812 this example we have a single user table that carries a boolean bit
813 for admin. We would like like to give the admin users
814 objects (L<DBIx::Class::Row>) the same methods as a regular user but
815 also special admin only methods. It doesn't make sense to create two
816 seperate proxy-class files for this. We would be copying all the user
817 methods into the Admin class. There is a cleaner way to accomplish
820 Overriding the C<inflate_result> method within the User proxy-class
821 gives us the effect we want. This method is called by
822 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
823 grab the object being returned, inspect the values we are looking for,
824 bless it if it's an admin object, and then return it. See the example
831 use base qw/DBIx::Class::Schema/;
833 __PACKAGE__->load_namespaces;
838 B<Proxy-Class definitions>
840 package My::Schema::Result::User;
844 use base qw/DBIx::Class::Core/;
846 ### Define what our admin class is, for ensure_class_loaded()
847 my $admin_class = __PACKAGE__ . '::Admin';
849 __PACKAGE__->table('users');
851 __PACKAGE__->add_columns(qw/user_id email password
852 firstname lastname active
855 __PACKAGE__->set_primary_key('user_id');
859 my $ret = $self->next::method(@_);
860 if( $ret->admin ) {### If this is an admin, rebless for extra functions
861 $self->ensure_class_loaded( $admin_class );
862 bless $ret, $admin_class;
868 print "I am a regular user.\n";
875 package My::Schema::Result::User::Admin;
879 use base qw/My::Schema::Result::User/;
881 # This line is important
882 __PACKAGE__->table('users');
886 print "I am an admin.\n";
892 print "I am doing admin stuff\n";
904 my $user_data = { email => 'someguy@place.com',
908 my $admin_data = { email => 'someadmin@adminplace.com',
912 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
914 $schema->resultset('User')->create( $user_data );
915 $schema->resultset('User')->create( $admin_data );
917 ### Now we search for them
918 my $user = $schema->resultset('User')->single( $user_data );
919 my $admin = $schema->resultset('User')->single( $admin_data );
921 print ref $user, "\n";
922 print ref $admin, "\n";
924 print $user->password , "\n"; # pass1
925 print $admin->password , "\n";# pass2; inherited from User
926 print $user->hello , "\n";# I am a regular user.
927 print $admin->hello, "\n";# I am an admin.
929 ### The statement below will NOT print
930 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
931 ### The statement below will print
932 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
934 Alternatively you can use L<DBIx::Class::DynamicSubclass> that implements
935 exactly the above functionality.
937 =head2 Skip row object creation for faster results
939 DBIx::Class is not built for speed, it's built for convenience and
940 ease of use, but sometimes you just need to get the data, and skip the
943 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
945 my $rs = $schema->resultset('CD');
947 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
949 my $hash_ref = $rs->find(1);
953 Beware, changing the Result class using
954 L<DBIx::Class::ResultSet/result_class> will replace any existing class
955 completely including any special components loaded using
956 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
958 =head2 Get raw data for blindingly fast results
960 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
961 above is not fast enough for you, you can use a DBIx::Class to return values
962 exactly as they come out of the database with none of the convenience methods
965 This is used like so:
967 my $cursor = $rs->cursor
968 while (my @vals = $cursor->next) {
969 # use $val[0..n] here
972 You will need to map the array offsets to particular columns (you can
973 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
975 =head1 RESULTSET OPERATIONS
977 =head2 Getting Schema from a ResultSet
979 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
981 $rs->result_source->schema
983 =head2 Getting Columns Of Data
987 If you want to find the sum of a particular column there are several
988 ways, the obvious one is to use search:
990 my $rs = $schema->resultset('Items')->search(
993 select => [ { sum => 'Cost' } ],
994 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
997 my $tc = $rs->first->get_column('total_cost');
999 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
1000 returned when you ask the C<ResultSet> for a column using
1003 my $cost = $schema->resultset('Items')->get_column('Cost');
1004 my $tc = $cost->sum;
1006 With this you can also do:
1008 my $minvalue = $cost->min;
1009 my $maxvalue = $cost->max;
1011 Or just iterate through the values of this column only:
1013 while ( my $c = $cost->next ) {
1017 foreach my $c ($cost->all) {
1021 C<ResultSetColumn> only has a limited number of built-in functions. If
1022 you need one that it doesn't have, then you can use the C<func> method
1025 my $avg = $cost->func('AVERAGE');
1027 This will cause the following SQL statement to be run:
1029 SELECT AVERAGE(Cost) FROM Items me
1031 Which will of course only work if your database supports this function.
1032 See L<DBIx::Class::ResultSetColumn> for more documentation.
1034 =head2 Creating a result set from a set of rows
1036 Sometimes you have a (set of) row objects that you want to put into a
1037 resultset without the need to hit the DB again. You can do that by using the
1038 L<set_cache|DBIx::Class::Resultset/set_cache> method:
1040 my @uploadable_groups;
1041 while (my $group = $groups->next) {
1042 if ($group->can_upload($self)) {
1043 push @uploadable_groups, $group;
1046 my $new_rs = $self->result_source->resultset;
1047 $new_rs->set_cache(\@uploadable_groups);
1051 =head1 USING RELATIONSHIPS
1053 =head2 Create a new row in a related table
1055 my $author = $book->create_related('author', { name => 'Fred'});
1057 =head2 Search in a related table
1059 Only searches for books named 'Titanic' by the author in $author.
1061 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1063 =head2 Delete data in a related table
1065 Deletes only the book named Titanic by the author in $author.
1067 $author->delete_related('books', { name => 'Titanic' });
1069 =head2 Ordering a relationship result set
1071 If you always want a relation to be ordered, you can specify this when you
1072 create the relationship.
1074 To order C<< $book->pages >> by descending page_number, create the relation
1077 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
1079 =head2 Filtering a relationship result set
1081 If you want to get a filtered result set, you can just add add to $attr as follows:
1083 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1085 =head2 Many-to-many relationships
1087 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1090 use base 'DBIx::Class::Core';
1091 __PACKAGE__->table('user');
1092 __PACKAGE__->add_columns(qw/id name/);
1093 __PACKAGE__->set_primary_key('id');
1094 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1095 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1097 package My::UserAddress;
1098 use base 'DBIx::Class::Core';
1099 __PACKAGE__->table('user_address');
1100 __PACKAGE__->add_columns(qw/user address/);
1101 __PACKAGE__->set_primary_key(qw/user address/);
1102 __PACKAGE__->belongs_to('user' => 'My::User');
1103 __PACKAGE__->belongs_to('address' => 'My::Address');
1105 package My::Address;
1106 use base 'DBIx::Class::Core';
1107 __PACKAGE__->table('address');
1108 __PACKAGE__->add_columns(qw/id street town area_code country/);
1109 __PACKAGE__->set_primary_key('id');
1110 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1111 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1113 $rs = $user->addresses(); # get all addresses for a user
1114 $rs = $address->users(); # get all users for an address
1116 my $address = $user->add_to_addresses( # returns a My::Address instance,
1117 # NOT a My::UserAddress instance!
1119 country => 'United Kingdom',
1126 =head2 Relationships across DB schemas
1128 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1129 is easy as long as the schemas themselves are all accessible via the same DBI
1130 connection. In most cases, this means that they are on the same database host
1131 as each other and your connecting database user has the proper permissions to them.
1133 To accomplish this one only needs to specify the DB schema name in the table
1134 declaration, like so...
1136 package MyDatabase::Main::Artist;
1137 use base qw/DBIx::Class::Core/;
1139 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1141 __PACKAGE__->add_columns(qw/ artist_id name /);
1142 __PACKAGE__->set_primary_key('artist_id');
1143 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1147 Whatever string you specify there will be used to build the "FROM" clause in SQL
1150 The big drawback to this is you now have DB schema names hardcoded in your
1151 class files. This becomes especially troublesome if you have multiple instances
1152 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1153 the DB schemas are named based on the environment (e.g. database1_dev).
1155 However, one can dynamically "map" to the proper DB schema by overriding the
1156 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1157 building a renaming facility, like so:
1159 package MyDatabase::Schema;
1162 extends 'DBIx::Class::Schema';
1164 around connection => sub {
1165 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1167 my $postfix = delete $attr->{schema_name_postfix};
1172 $self->append_db_name($postfix);
1176 sub append_db_name {
1177 my ( $self, $postfix ) = @_;
1181 { $_->name =~ /^\w+\./mx }
1183 { $self->source($_) }
1186 foreach my $source (@sources_with_db) {
1187 my $name = $source->name;
1188 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1190 $source->name($name);
1196 By overridding the L<connection|DBIx::Class::Schama/connection>
1197 method and extracting a custom option from the provided \%attr hashref one can
1198 then simply iterate over all the Schema's ResultSources, renaming them as
1201 To use this facility, simply add or modify the \%attr hashref that is passed to
1202 L<connection|DBIx::Class::Schama/connect>, as follows:
1205 = MyDatabase::Schema->connect(
1210 schema_name_postfix => '_dev'
1211 # ... Other options as desired ...
1214 Obviously, one could accomplish even more advanced mapping via a hash map or a
1219 As of version 0.04001, there is improved transaction support in
1220 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1221 example of the recommended way to use it:
1223 my $genus = $schema->resultset('Genus')->find(12);
1225 my $coderef2 = sub {
1230 my $coderef1 = sub {
1231 $genus->add_to_species({ name => 'troglodyte' });
1234 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1235 return $genus->species;
1240 $rs = $schema->txn_do($coderef1);
1243 if ($@) { # Transaction failed
1244 die "the sky is falling!" #
1245 if ($@ =~ /Rollback failed/); # Rollback failed
1247 deal_with_failed_transaction();
1250 Nested transactions will work as expected. That is, only the outermost
1251 transaction will actually issue a commit to the $dbh, and a rollback
1252 at any level of any transaction will cause the entire nested
1253 transaction to fail.
1255 =head2 Nested transactions and auto-savepoints
1257 If savepoints are supported by your RDBMS, it is possible to achieve true
1258 nested transactions with minimal effort. To enable auto-savepoints via nested
1259 transactions, supply the C<< auto_savepoint = 1 >> connection attribute.
1261 Here is an example of true nested transactions. In the example, we start a big
1262 task which will create several rows. Generation of data for each row is a
1263 fragile operation and might fail. If we fail creating something, depending on
1264 the type of failure, we want to abort the whole task, or only skip the failed
1267 my $schema = MySchema->connect("dbi:Pg:dbname=my_db");
1269 # Start a transaction. Every database change from here on will only be
1270 # commited into the database if the eval block succeeds.
1272 $schema->txn_do(sub {
1275 my $job = $schema->resultset('Job')->create({ name=> 'big job' });
1276 # SQL: INSERT INTO job ( name) VALUES ( 'big job' );
1280 # Start a nested transaction, which in fact sets a savepoint.
1282 $schema->txn_do(sub {
1283 # SQL: SAVEPOINT savepoint_0;
1285 my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
1286 # SQL: INSERT INTO thing ( job) VALUES ( 1 );
1289 # This will generate an error, thus setting $@
1291 $thing->update({force_fail=>'foo'});
1292 # SQL: UPDATE thing SET force_fail = 'foo'
1293 # WHERE ( id = 42 );
1298 # SQL: ROLLBACK TO SAVEPOINT savepoint_0;
1300 # There was an error while creating a $thing. Depending on the error
1301 # we want to abort the whole transaction, or only rollback the
1302 # changes related to the creation of this $thing
1304 # Abort the whole job
1305 if ($@ =~ /horrible_problem/) {
1306 print "something horrible happend, aborting job!";
1307 die $@; # rethrow error
1310 # Ignore this $thing, report the error, and continue with the
1312 print "Cannot create thing: $@";
1314 # There was no error, so save all changes since the last
1317 # SQL: RELEASE SAVEPOINT savepoint_0;
1322 # There was an error while handling the $job. Rollback all changes
1323 # since the transaction started, including the already commited
1324 # ('released') savepoints. There will be neither a new $job nor any
1325 # $thing entry in the database.
1329 print "ERROR: $@\n";
1332 # There was no error while handling the $job. Commit all changes.
1333 # Only now other connections can see the newly created $job and
1341 In this example it might be hard to see where the rollbacks, releases and
1342 commits are happening, but it works just the same as for plain L<<txn_do>>: If
1343 the C<eval>-block around C<txn_do> fails, a rollback is issued. If the C<eval>
1344 succeeds, the transaction is committed (or the savepoint released).
1346 While you can get more fine-grained controll using C<svp_begin>, C<svp_release>
1347 and C<svp_rollback>, it is strongly recommended to use C<txn_do> with coderefs.
1351 =head2 Creating Schemas From An Existing Database
1353 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1354 L<DBIx::Class::Schema> and associated sources by examining the database.
1356 The recommend way of achieving this is to use the
1357 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1359 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1360 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1362 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1363 source definitions for all the tables found in the C<foo> database.
1365 =head2 Creating DDL SQL
1367 The following functionality requires you to have L<SQL::Translator>
1368 (also known as "SQL Fairy") installed.
1370 To create a set of database-specific .sql files for the above schema:
1372 my $schema = My::Schema->connect($dsn);
1373 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1378 By default this will create schema files in the current directory, for
1379 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1381 To create a new database using the schema:
1383 my $schema = My::Schema->connect($dsn);
1384 $schema->deploy({ add_drop_table => 1});
1386 To import created .sql files using the mysql client:
1388 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1390 To create C<ALTER TABLE> conversion scripts to update a database to a
1391 newer version of your schema at a later point, first set a new
1392 C<$VERSION> in your Schema file, then:
1394 my $schema = My::Schema->connect($dsn);
1395 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1401 This will produce new database-specific .sql files for the new version
1402 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1403 requires that the files for 0.1 as created above are available in the
1404 given directory to diff against.
1406 =head2 Select from dual
1408 Dummy tables are needed by some databases to allow calling functions
1409 or expressions that aren't based on table content, for examples of how
1410 this applies to various database types, see:
1411 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1413 Note: If you're using Oracles dual table don't B<ever> do anything
1414 other than a select, if you CRUD on your dual table you *will* break
1417 Make a table class as you would for any other table
1419 package MyAppDB::Dual;
1422 use base 'DBIx::Class::Core';
1423 __PACKAGE__->table("Dual");
1424 __PACKAGE__->add_columns(
1426 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1429 Once you've loaded your table class select from it using C<select>
1430 and C<as> instead of C<columns>
1432 my $rs = $schema->resultset('Dual')->search(undef,
1433 { select => [ 'sydate' ],
1438 All you have to do now is be careful how you access your resultset, the below
1439 will not work because there is no column called 'now' in the Dual table class
1441 while (my $dual = $rs->next) {
1442 print $dual->now."\n";
1444 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1446 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1447 your Dual class for whatever you wanted to select from dual, but that's just
1448 silly, instead use C<get_column>
1450 while (my $dual = $rs->next) {
1451 print $dual->get_column('now')."\n";
1456 my $cursor = $rs->cursor;
1457 while (my @vals = $cursor->next) {
1458 print $vals[0]."\n";
1461 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1462 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1463 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1464 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1465 L<SQL::Translator> to not create table dual:
1468 add_drop_table => 1,
1469 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1471 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1473 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1475 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1476 while ( my $dual = $rs->next ) {
1477 print $dual->{now}."\n";
1480 Here are some example C<select> conditions to illustrate the different syntax
1481 you could use for doing stuff like
1482 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1484 # get a sequence value
1485 select => [ 'A_SEQ.nextval' ],
1487 # get create table sql
1488 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1490 # get a random num between 0 and 100
1491 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1494 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1497 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1499 # which day of the week were you born on?
1500 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1502 # select 16 rows from dual
1503 select => [ "'hello'" ],
1505 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1509 =head2 Adding Indexes And Functions To Your SQL
1511 Often you will want indexes on columns on your table to speed up searching. To
1512 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1513 class (refer to the advanced
1514 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1515 to share a hook between multiple sources):
1517 package My::Schema::Result::Artist;
1519 __PACKAGE__->table('artist');
1520 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1522 sub sqlt_deploy_hook {
1523 my ($self, $sqlt_table) = @_;
1525 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1530 Sometimes you might want to change the index depending on the type of the
1531 database for which SQL is being generated:
1533 my ($db_type = $sqlt_table->schema->translator->producer_type)
1534 =~ s/^SQL::Translator::Producer:://;
1536 You can also add hooks to the schema level to stop certain tables being
1543 sub sqlt_deploy_hook {
1544 my ($self, $sqlt_schema) = @_;
1546 $sqlt_schema->drop_table('table_name');
1549 You could also add views, procedures or triggers to the output using
1550 L<SQL::Translator::Schema/add_view>,
1551 L<SQL::Translator::Schema/add_procedure> or
1552 L<SQL::Translator::Schema/add_trigger>.
1555 =head2 Schema versioning
1557 The following example shows simplistically how you might use DBIx::Class to
1558 deploy versioned schemas to your customers. The basic process is as follows:
1564 Create a DBIx::Class schema
1576 Modify schema to change functionality
1580 Deploy update to customers
1584 B<Create a DBIx::Class schema>
1586 This can either be done manually, or generated from an existing database as
1587 described under L</Creating Schemas From An Existing Database>
1591 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1593 B<Deploy to customers>
1595 There are several ways you could deploy your schema. These are probably
1596 beyond the scope of this recipe, but might include:
1602 Require customer to apply manually using their RDBMS.
1606 Package along with your app, making database dump/schema update/tests
1607 all part of your install.
1611 B<Modify the schema to change functionality>
1613 As your application evolves, it may be necessary to modify your schema
1614 to change functionality. Once the changes are made to your schema in
1615 DBIx::Class, export the modified schema and the conversion scripts as
1616 in L</Creating DDL SQL>.
1618 B<Deploy update to customers>
1620 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1621 Schema class. This will add a new table to your database called
1622 C<dbix_class_schema_vesion> which will keep track of which version is installed
1623 and warn if the user trys to run a newer schema version than the
1624 database thinks it has.
1626 Alternatively, you can send the conversion sql scripts to your
1629 =head2 Setting quoting for the generated SQL
1631 If the database contains column names with spaces and/or reserved words, they
1632 need to be quoted in the SQL queries. This is done using:
1634 $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
1635 $schema->storage->sql_maker->name_sep('.');
1637 The first sets the quote characters. Either a pair of matching
1638 brackets, or a C<"> or C<'>:
1640 $schema->storage->sql_maker->quote_char('"');
1642 Check the documentation of your database for the correct quote
1643 characters to use. C<name_sep> needs to be set to allow the SQL
1644 generator to put the quotes the correct place.
1646 In most cases you should set these as part of the arguments passed to
1647 L<DBIx::Class::Schema/connect>:
1649 my $schema = My::Schema->connect(
1659 In some cases, quoting will be required for all users of a schema. To enforce
1660 this, you can also overload the C<connection> method for your schema class:
1664 my $rv = $self->next::method( @_ );
1665 $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
1666 $rv->storage->sql_maker->name_sep('.');
1670 =head2 Setting limit dialect for SQL::Abstract::Limit
1672 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1673 the remote SQL server by looking at the database handle. This is a
1674 common problem when using the DBD::JDBC, since the DBD-driver only
1675 know that in has a Java-driver available, not which JDBC driver the
1676 Java component has loaded. This specifically sets the limit_dialect
1677 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1680 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1682 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1683 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1685 The limit dialect can also be set at connect time by specifying a
1686 C<limit_dialect> key in the final hash as shown above.
1688 =head2 Working with PostgreSQL array types
1690 You can also assign values to PostgreSQL array columns by passing array
1691 references in the C<\%columns> (C<\%vals>) hashref of the
1692 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1695 $resultset->create({
1696 numbers => [1, 2, 3]
1701 numbers => [1, 2, 3]
1708 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1709 methods) you cannot directly use array references (since this is interpreted as
1710 a list of values to be C<OR>ed), but you can use the following syntax to force
1711 passing them as bind values:
1715 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1719 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1720 placeholders and bind values (subqueries)> for more explanation. Note that
1721 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1722 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1723 arrayrefs together with the column name, like this: C<< [column_name => value]
1726 =head1 BOOTSTRAPPING/MIGRATING
1728 =head2 Easy migration from class-based to schema-based setup
1730 You want to start using the schema-based approach to L<DBIx::Class>
1731 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1732 of existing classes that you don't want to move by hand. Try this nifty script
1736 use SQL::Translator;
1738 my $schema = MyDB->schema_instance;
1740 my $translator = SQL::Translator->new(
1741 debug => $debug || 0,
1742 trace => $trace || 0,
1743 no_comments => $no_comments || 0,
1744 show_warnings => $show_warnings || 0,
1745 add_drop_table => $add_drop_table || 0,
1746 validate => $validate || 0,
1748 'DBIx::Schema' => $schema,
1751 'prefix' => 'My::Schema',
1755 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1756 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1758 my $output = $translator->translate(@args) or die
1759 "Error: " . $translator->error;
1763 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1764 namespace, which is currently left as an exercise for the reader.
1766 =head1 OVERLOADING METHODS
1768 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1769 method calls, useful for things like default values and triggers. You have to
1770 use calls to C<next::method> to overload methods. More information on using
1771 L<Class::C3> with L<DBIx::Class> can be found in
1772 L<DBIx::Class::Manual::Component>.
1774 =head2 Setting default values for a row
1776 It's as simple as overriding the C<new> method. Note the use of
1780 my ( $class, $attrs ) = @_;
1782 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1784 my $new = $class->next::method($attrs);
1789 For more information about C<next::method>, look in the L<Class::C3>
1790 documentation. See also L<DBIx::Class::Manual::Component> for more
1791 ways to write your own base classes to do this.
1793 People looking for ways to do "triggers" with DBIx::Class are probably
1794 just looking for this.
1796 =head2 Changing one field whenever another changes
1798 For example, say that you have three columns, C<id>, C<number>, and
1799 C<squared>. You would like to make changes to C<number> and have
1800 C<squared> be automagically set to the value of C<number> squared.
1801 You can accomplish this by overriding C<store_column>:
1804 my ( $self, $name, $value ) = @_;
1805 if ($name eq 'number') {
1806 $self->squared($value * $value);
1808 $self->next::method($name, $value);
1811 Note that the hard work is done by the call to C<next::method>, which
1812 redispatches your call to store_column in the superclass(es).
1814 =head2 Automatically creating related objects
1816 You might have a class C<Artist> which has many C<CD>s. Further, you
1817 want to create a C<CD> object every time you insert an C<Artist> object.
1818 You can accomplish this by overriding C<insert> on your objects:
1821 my ( $self, @args ) = @_;
1822 $self->next::method(@args);
1823 $self->cds->new({})->fill_from_artist($self)->insert;
1827 where C<fill_from_artist> is a method you specify in C<CD> which sets
1828 values in C<CD> based on the data in the C<Artist> object you pass in.
1830 =head2 Wrapping/overloading a column accessor
1834 Say you have a table "Camera" and want to associate a description
1835 with each camera. For most cameras, you'll be able to generate the description from
1836 the other columns. However, in a few special cases you may want to associate a
1837 custom description with a camera.
1841 In your database schema, define a description field in the "Camera" table that
1842 can contain text and null values.
1844 In DBIC, we'll overload the column accessor to provide a sane default if no
1845 custom description is defined. The accessor will either return or generate the
1846 description, depending on whether the field is null or not.
1848 First, in your "Camera" schema class, define the description field as follows:
1850 __PACKAGE__->add_columns(description => { accessor => '_description' });
1852 Next, we'll define the accessor-wrapper subroutine:
1857 # If there is an update to the column, we'll let the original accessor
1859 return $self->_description(@_) if @_;
1861 # Fetch the column value.
1862 my $description = $self->_description;
1864 # If there's something in the description field, then just return that.
1865 return $description if defined $description && length $descripton;
1867 # Otherwise, generate a description.
1868 return $self->generate_description;
1871 =head1 DEBUGGING AND PROFILING
1873 =head2 DBIx::Class objects with Data::Dumper
1875 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1876 be hard to find the pertinent data in all the data it can generate.
1877 Specifically, if one naively tries to use it like so,
1881 my $cd = $schema->resultset('CD')->find(1);
1884 several pages worth of data from the CD object's schema and result source will
1885 be dumped to the screen. Since usually one is only interested in a few column
1886 values of the object, this is not very helpful.
1888 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1889 it. Simply define a hook that L<Data::Dumper> will call on the object before
1890 dumping it. For example,
1897 result_source => undef,
1905 local $Data::Dumper::Freezer = '_dumper_hook';
1907 my $cd = $schema->resultset('CD')->find(1);
1909 # dumps $cd without its ResultSource
1911 If the structure of your schema is such that there is a common base class for
1912 all your table classes, simply put a method similar to C<_dumper_hook> in the
1913 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1914 will automagically clean up your data before printing it. See
1915 L<Data::Dumper/EXAMPLES> for more information.
1919 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1920 executed as well as notifications of query completion and transaction
1921 begin/commit. If you'd like to profile the SQL you can subclass the
1922 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1925 package My::Profiler;
1928 use base 'DBIx::Class::Storage::Statistics';
1930 use Time::HiRes qw(time);
1939 $self->print("Executing $sql: ".join(', ', @params)."\n");
1948 my $elapsed = sprintf("%0.4f", time() - $start);
1949 $self->print("Execution took $elapsed seconds.\n");
1955 You can then install that class as the debugging object:
1957 __PACKAGE__->storage->debugobj(new My::Profiler());
1958 __PACKAGE__->storage->debug(1);
1960 A more complicated example might involve storing each execution of SQL in an
1968 my $elapsed = time() - $start;
1969 push(@{ $calls{$sql} }, {
1975 You could then create average, high and low execution times for an SQL
1976 statement and dig down to see if certain parameters cause aberrant behavior.
1977 You might want to check out L<DBIx::Class::QueryLog> as well.
1979 =head1 STARTUP SPEED
1981 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1982 as the ORM loads all the relevant classes. This section examines
1983 techniques for reducing the startup delay.
1985 These tips are are listed in order of decreasing effectiveness - so the
1986 first tip, if applicable, should have the greatest effect on your
1989 =head2 Statically Define Your Schema
1992 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1993 classes dynamically based on the database schema then there will be a
1994 significant startup delay.
1996 For production use a statically defined schema (which can be generated
1997 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1998 the database schema once - see
1999 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
2000 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
2001 details on creating static schemas from a database).
2003 =head2 Move Common Startup into a Base Class
2005 Typically L<DBIx::Class> result classes start off with
2007 use base qw/DBIx::Class::Core/;
2008 __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2010 If this preamble is moved into a common base class:-
2014 use base qw/DBIx::Class::Core/;
2015 __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2018 and each result class then uses this as a base:-
2020 use base qw/MyDBICbase/;
2022 then the load_components is only performed once, which can result in a
2023 considerable startup speedup for schemas with many classes.
2025 =head2 Explicitly List Schema Result Classes
2027 The schema class will normally contain
2029 __PACKAGE__->load_classes();
2031 to load the result classes. This will use L<Module::Find|Module::Find>
2032 to find and load the appropriate modules. Explicitly defining the
2033 classes you wish to load will remove the overhead of
2034 L<Module::Find|Module::Find> and the related directory operations:
2036 __PACKAGE__->load_classes(qw/ CD Artist Track /);
2038 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
2039 syntax to load the appropriate classes there is not a direct alternative
2040 avoiding L<Module::Find|Module::Find>.
2044 =head2 Cached statements
2046 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
2047 This is normally a good idea, but if too many statements are cached, the database may use too much
2048 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
2049 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
2051 # print all currently cached prepared statements
2052 print for keys %{$schema->storage->dbh->{CachedKids}};
2053 # get a count of currently cached prepared statements
2054 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
2056 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
2059 my $kids = $schema->storage->dbh->{CachedKids};
2060 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
2062 But what you probably want is to expire unused statements and not those that are used frequently.
2063 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
2067 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
2068 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },