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 The C<page> attribute does not have to be specified in your search:
24 my $rs = $schema->resultset('Artist')->search(
31 return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records
33 In either of the above cases, you can get a L<Data::Page> object for the
34 resultset (suitable for use in e.g. a template) using the C<pager> method:
38 =head2 Complex WHERE clauses
40 Sometimes you need to formulate a query using specific operators:
42 my @albums = $schema->resultset('Album')->search({
43 artist => { 'like', '%Lamb%' },
44 title => { 'like', '%Fear of Fours%' },
47 This results in something like the following C<WHERE> clause:
49 WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
51 Other queries might require slightly more complex logic:
53 my @albums = $schema->resultset('Album')->search({
56 artist => { 'like', '%Smashing Pumpkins%' },
57 title => 'Siamese Dream',
59 artist => 'Starchildren',
63 This results in the following C<WHERE> clause:
65 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
66 OR artist = 'Starchildren'
68 For more information on generating complex queries, see
69 L<SQL::Abstract/WHERE CLAUSES>.
71 =head2 Retrieve one and only one row from a resultset
73 Sometimes you need only the first "top" row of a resultset. While this can be
74 easily done with L<< $rs->first|DBIx::Class::ResultSet/first >>, it is suboptimal,
75 as a full blown cursor for the resultset will be created and then immediately
76 destroyed after fetching the first row object.
77 L<< $rs->single|DBIx::Class::ResultSet/single >> is
78 designed specifically for this case - it will grab the first returned result
79 without even instantiating a cursor.
81 Before replacing all your calls to C<first()> with C<single()> please observe the
87 While single() takes a search condition just like search() does, it does
88 _not_ accept search attributes. However one can always chain a single() to
91 my $top_cd = $cd_rs -> search({}, { order_by => 'rating' }) -> single;
95 Since single() is the engine behind find(), it is designed to fetch a
96 single row per database query. Thus a warning will be issued when the
97 underlying SELECT returns more than one row. Sometimes however this usage
98 is valid: i.e. we have an arbitrary number of cd's but only one of them is
99 at the top of the charts at any given time. If you know what you are doing,
100 you can silence the warning by explicitly limiting the resultset size:
102 my $top_cd = $cd_rs -> search ({}, { order_by => 'rating', rows => 1 }) -> single;
106 =head2 Arbitrary SQL through a custom ResultSource
108 Sometimes you have to run arbitrary SQL because your query is too complex
109 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
110 be optimized for your database in a special way, but you still want to
111 get the results as a L<DBIx::Class::ResultSet>.
112 The recommended way to accomplish this is by defining a separate ResultSource
113 for your query. You can then inject complete SQL statements using a scalar
114 reference (this is a feature of L<SQL::Abstract>).
116 Say you want to run a complex custom query on your user data, here's what
117 you have to add to your User class:
119 package My::Schema::User;
121 use base qw/DBIx::Class/;
123 # ->load_components, ->table, ->add_columns, etc.
125 # Make a new ResultSource based on the User class
126 my $source = __PACKAGE__->result_source_instance();
127 my $new_source = $source->new( $source );
128 $new_source->source_name( 'UserFriendsComplex' );
130 # Hand in your query as a scalar reference
131 # It will be added as a sub-select after FROM,
132 # so pay attention to the surrounding brackets!
133 $new_source->name( \<<SQL );
134 ( SELECT u.* FROM user u
135 INNER JOIN user_friends f ON u.id = f.user_id
136 WHERE f.friend_user_id = ?
138 SELECT u.* FROM user u
139 INNER JOIN user_friends f ON u.id = f.friend_user_id
140 WHERE f.user_id = ? )
143 # Finally, register your new ResultSource with your Schema
144 My::Schema->register_extra_source( 'UserFriendsComplex' => $new_source );
146 Next, you can execute your complex query using bind parameters like this:
148 my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {},
150 bind => [ 12345, 12345 ]
154 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
155 that you cannot modify the rows it contains, ie. cannot call L</update>,
156 L</delete>, ... on it).
158 If you prefer to have the definitions of these custom ResultSources in separate
159 files (instead of stuffing all of them into the same resultset class), you can
160 achieve the same with subclassing the resultset class and defining the
163 package My::Schema::UserFriendsComplex;
165 use My::Schema::User;
166 use base qw/My::Schema::User/;
168 __PACKAGE__->table('dummy'); # currently must be called before anything else
170 # Hand in your query as a scalar reference
171 # It will be added as a sub-select after FROM,
172 # so pay attention to the surrounding brackets!
173 __PACKAGE__->name( \<<SQL );
174 ( SELECT u.* FROM user u
175 INNER JOIN user_friends f ON u.id = f.user_id
176 WHERE f.friend_user_id = ?
178 SELECT u.* FROM user u
179 INNER JOIN user_friends f ON u.id = f.friend_user_id
180 WHERE f.user_id = ? )
185 =head2 Using specific columns
187 When you only want specific columns from a table, you can use
188 C<columns> to specify which ones you need. This is useful to avoid
189 loading columns with large amounts of data that you aren't about to
192 my $rs = $schema->resultset('Artist')->search(
195 columns => [qw/ name /]
200 # SELECT artist.name FROM artist
202 This is a shortcut for C<select> and C<as>, see below. C<columns>
203 cannot be used together with C<select> and C<as>.
205 =head2 Using database functions or stored procedures
207 The combination of C<select> and C<as> can be used to return the result of a
208 database function or stored procedure as a column value. You use C<select> to
209 specify the source for your column value (e.g. a column name, function, or
210 stored procedure name). You then use C<as> to set the column name you will use
211 to access the returned value:
213 my $rs = $schema->resultset('Artist')->search(
216 select => [ 'name', { LENGTH => 'name' } ],
217 as => [qw/ name name_length /],
222 # SELECT name name, LENGTH( name )
225 Note that the C< as > attribute has absolutely nothing to with the sql
226 syntax C< SELECT foo AS bar > (see the documentation in
227 L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
228 column in your base class (i.e. it was added with C<add_columns>), you
229 just access it as normal. Our C<Artist> class has a C<name> column, so
230 we just use the C<name> accessor:
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 =head2 SELECT DISTINCT with multiple columns
251 my $rs = $schema->resultset('Foo')->search(
255 { distinct => [ $source->columns ] }
257 as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
261 =head2 SELECT COUNT(DISTINCT colname)
263 my $rs = $schema->resultset('Foo')->search(
267 { count => { distinct => 'colname' } }
273 my $count = $rs->next->get_column('count');
275 =head2 Grouping results
277 L<DBIx::Class> supports C<GROUP BY> as follows:
279 my $rs = $schema->resultset('Artist')->search(
283 select => [ 'name', { count => 'cds.id' } ],
284 as => [qw/ name cd_count /],
285 group_by => [qw/ name /]
290 # SELECT name, COUNT( cd.id ) FROM artist
291 # LEFT JOIN cd ON artist.id = cd.artist
294 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
295 are in any way unsure about the use of the attributes above (C< join
296 >, C< select >, C< as > and C< group_by >).
300 You can write subqueries relatively easily in DBIC.
302 my $inside_rs = $schema->resultset('Artist')->search({
303 name => [ 'Billy Joel', 'Brittany Spears' ],
306 my $rs = $schema->resulset('CD')->search({
307 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
310 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
312 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
313 The following will B<not> work:
315 my $rs = $schema->resulset('CD')->search({
316 artist_id => $inside_rs->get_column('id')->as_query,
319 =head2 Predefined searches
321 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
322 and define often used searches as methods:
324 package My::DBIC::ResultSet::CD;
327 use base 'DBIx::Class::ResultSet';
329 sub search_cds_ordered {
332 return $self->search(
334 { order_by => 'name DESC' },
340 To use your resultset, first tell DBIx::Class to create an instance of it
341 for you, in your My::DBIC::Schema::CD class:
343 # class definition as normal
344 __PACKAGE__->load_components(qw/ Core /);
345 __PACKAGE__->table('cd');
347 # tell DBIC to use the custom ResultSet class
348 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
350 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
352 Then call your new method in your code:
354 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
356 =head2 Using SQL functions on the left hand side of a comparison
358 Using SQL functions on the left hand side of a comparison is generally
359 not a good idea since it requires a scan of the entire table. However,
360 it can be accomplished with C<DBIx::Class> when necessary.
362 If you do not have quoting on, simply include the function in your search
363 specification as you would any column:
365 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
367 With quoting on, or for a more portable solution, use the C<where>
370 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
374 (When the bind args ordering bug is fixed, this technique will be better
375 and can replace the one above.)
377 With quoting on, or for a more portable solution, use the C<where> and
381 where => \'YEAR(date_of_birth) = ?',
387 =head1 JOINS AND PREFETCHING
389 =head2 Using joins and prefetch
391 You can use the C<join> attribute to allow searching on, or sorting your
392 results by, one or more columns in a related table. To return all CDs matching
393 a particular artist name:
395 my $rs = $schema->resultset('CD')->search(
397 'artist.name' => 'Bob Marley'
400 join => 'artist', # join the artist table
405 # SELECT cd.* FROM cd
406 # JOIN artist ON cd.artist = artist.id
407 # WHERE artist.name = 'Bob Marley'
409 If required, you can now sort on any column in the related tables by including
410 it in your C<order_by> attribute:
412 my $rs = $schema->resultset('CD')->search(
414 'artist.name' => 'Bob Marley'
418 order_by => [qw/ artist.name /]
423 # SELECT cd.* FROM cd
424 # JOIN artist ON cd.artist = artist.id
425 # WHERE artist.name = 'Bob Marley'
426 # ORDER BY artist.name
428 Note that the C<join> attribute should only be used when you need to search or
429 sort using columns in a related table. Joining related tables when you only
430 need columns from the main table will make performance worse!
432 Now let's say you want to display a list of CDs, each with the name of the
433 artist. The following will work fine:
435 while (my $cd = $rs->next) {
436 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
439 There is a problem however. We have searched both the C<cd> and C<artist> tables
440 in our main query, but we have only returned data from the C<cd> table. To get
441 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
444 SELECT artist.* FROM artist WHERE artist.id = ?
446 A statement like the one above will run for each and every CD returned by our
447 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
450 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
451 This allows you to fetch results from related tables in advance:
453 my $rs = $schema->resultset('CD')->search(
455 'artist.name' => 'Bob Marley'
459 order_by => [qw/ artist.name /],
460 prefetch => 'artist' # return artist data too!
464 # Equivalent SQL (note SELECT from both "cd" and "artist"):
465 # SELECT cd.*, artist.* FROM cd
466 # JOIN artist ON cd.artist = artist.id
467 # WHERE artist.name = 'Bob Marley'
468 # ORDER BY artist.name
470 The code to print the CD list remains the same:
472 while (my $cd = $rs->next) {
473 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
476 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
477 so no additional SQL statements are executed. You now have a much more
480 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
481 C<has_many> relationships.
483 Also note that C<prefetch> should only be used when you know you will
484 definitely use data from a related table. Pre-fetching related tables when you
485 only need columns from the main table will make performance worse!
487 =head2 Multiple joins
489 In the examples above, the C<join> attribute was a scalar. If you
490 pass an array reference instead, you can join to multiple tables. In
491 this example, we want to limit the search further, using
494 # Relationships defined elsewhere:
495 # CD->belongs_to('artist' => 'Artist');
496 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
497 my $rs = $schema->resultset('CD')->search(
499 'artist.name' => 'Bob Marley'
500 'liner_notes.notes' => { 'like', '%some text%' },
503 join => [qw/ artist liner_notes /],
504 order_by => [qw/ artist.name /],
509 # SELECT cd.*, artist.*, liner_notes.* FROM cd
510 # JOIN artist ON cd.artist = artist.id
511 # JOIN liner_notes ON cd.id = liner_notes.cd
512 # WHERE artist.name = 'Bob Marley'
513 # ORDER BY artist.name
515 =head2 Multi-step joins
517 Sometimes you want to join more than one relationship deep. In this example,
518 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
519 contain a specific string:
521 # Relationships defined elsewhere:
522 # Artist->has_many('cds' => 'CD', 'artist');
523 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
525 my $rs = $schema->resultset('Artist')->search(
527 'liner_notes.notes' => { 'like', '%some text%' },
531 'cds' => 'liner_notes'
537 # SELECT artist.* FROM artist
538 # LEFT JOIN cd ON artist.id = cd.artist
539 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
540 # WHERE liner_notes.notes LIKE '%some text%'
542 Joins can be nested to an arbitrary level. So if we decide later that we
543 want to reduce the number of Artists returned based on who wrote the liner
546 # Relationship defined elsewhere:
547 # LinerNotes->belongs_to('author' => 'Person');
549 my $rs = $schema->resultset('Artist')->search(
551 'liner_notes.notes' => { 'like', '%some text%' },
552 'author.name' => 'A. Writer'
557 'liner_notes' => 'author'
564 # SELECT artist.* FROM artist
565 # LEFT JOIN cd ON artist.id = cd.artist
566 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
567 # LEFT JOIN author ON author.id = liner_notes.author
568 # WHERE liner_notes.notes LIKE '%some text%'
569 # AND author.name = 'A. Writer'
571 =head2 Multi-step and multiple joins
573 With various combinations of array and hash references, you can join
574 tables in any combination you desire. For example, to join Artist to
575 CD and Concert, and join CD to LinerNotes:
577 # Relationships defined elsewhere:
578 # Artist->has_many('concerts' => 'Concert', 'artist');
580 my $rs = $schema->resultset('Artist')->search(
593 # SELECT artist.* FROM artist
594 # LEFT JOIN cd ON artist.id = cd.artist
595 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
596 # LEFT JOIN concert ON artist.id = concert.artist
598 =head2 Multi-step prefetch
600 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
601 deep using the same syntax as a multi-step join:
603 my $rs = $schema->resultset('Tag')->search(
613 # SELECT tag.*, cd.*, artist.* FROM tag
614 # JOIN cd ON tag.cd = cd.id
615 # JOIN artist ON cd.artist = artist.id
617 Now accessing our C<cd> and C<artist> relationships does not need additional
620 my $tag = $rs->first;
621 print $tag->cd->artist->name;
623 =head1 ROW-LEVEL OPERATIONS
625 =head2 Retrieving a row object's Schema
627 It is possible to get a Schema object from a row object like so:
629 my $schema = $cd->result_source->schema;
630 # use the schema as normal:
631 my $artist_rs = $schema->resultset('Artist');
633 This can be useful when you don't want to pass around a Schema object to every
636 =head2 Getting the value of the primary key for the last database insert
638 AKA getting last_insert_id
640 If you are using PK::Auto (which is a core component as of 0.07), this is
643 my $foo = $rs->create(\%blah);
645 my $id = $foo->id; # foo->my_primary_key_field will also work.
647 If you are not using autoincrementing primary keys, this will probably
648 not work, but then you already know the value of the last primary key anyway.
650 =head2 Stringification
652 Employ the standard stringification technique by using the C<overload>
655 To make an object stringify itself as a single column, use something
656 like this (replace C<foo> with the column/method of your choice):
658 use overload '""' => sub { shift->name}, fallback => 1;
660 For more complex stringification, you can use an anonymous subroutine:
662 use overload '""' => sub { $_[0]->name . ", " .
663 $_[0]->address }, fallback => 1;
665 =head3 Stringification Example
667 Suppose we have two tables: C<Product> and C<Category>. The table
670 Product(id, Description, category)
671 Category(id, Description)
673 C<category> is a foreign key into the Category table.
675 If you have a Product object C<$obj> and write something like
679 things will not work as expected.
681 To obtain, for example, the category description, you should add this
682 method to the class defining the Category table:
684 use overload "" => sub {
687 return $self->Description;
690 =head2 Want to know if find_or_create found or created a row?
692 Just use C<find_or_new> instead, then check C<in_storage>:
694 my $obj = $rs->find_or_new({ blah => 'blarg' });
695 unless ($obj->in_storage) {
697 # do whatever else you wanted if it was a new row
700 =head2 Dynamic Sub-classing DBIx::Class proxy classes
702 AKA multi-class object inflation from one table
704 L<DBIx::Class> classes are proxy classes, therefore some different
705 techniques need to be employed for more than basic subclassing. In
706 this example we have a single user table that carries a boolean bit
707 for admin. We would like like to give the admin users
708 objects(L<DBIx::Class::Row>) the same methods as a regular user but
709 also special admin only methods. It doesn't make sense to create two
710 seperate proxy-class files for this. We would be copying all the user
711 methods into the Admin class. There is a cleaner way to accomplish
714 Overriding the C<inflate_result> method within the User proxy-class
715 gives us the effect we want. This method is called by
716 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
717 grab the object being returned, inspect the values we are looking for,
718 bless it if it's an admin object, and then return it. See the example
725 use base qw/DBIx::Class::Schema/;
727 __PACKAGE__->load_classes(qw/User/);
730 B<Proxy-Class definitions>
732 package DB::Schema::User;
736 use base qw/DBIx::Class/;
738 ### Defined what our admin class is for ensure_class_loaded
739 my $admin_class = __PACKAGE__ . '::Admin';
741 __PACKAGE__->load_components(qw/Core/);
743 __PACKAGE__->table('users');
745 __PACKAGE__->add_columns(qw/user_id email password
746 firstname lastname active
749 __PACKAGE__->set_primary_key('user_id');
753 my $ret = $self->next::method(@_);
754 if( $ret->admin ) {### If this is an admin rebless for extra functions
755 $self->ensure_class_loaded( $admin_class );
756 bless $ret, $admin_class;
762 print "I am a regular user.\n";
767 package DB::Schema::User::Admin;
771 use base qw/DB::Schema::User/;
775 print "I am an admin.\n";
781 print "I am doing admin stuff\n";
791 my $user_data = { email => 'someguy@place.com',
795 my $admin_data = { email => 'someadmin@adminplace.com',
799 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
801 $schema->resultset('User')->create( $user_data );
802 $schema->resultset('User')->create( $admin_data );
804 ### Now we search for them
805 my $user = $schema->resultset('User')->single( $user_data );
806 my $admin = $schema->resultset('User')->single( $admin_data );
808 print ref $user, "\n";
809 print ref $admin, "\n";
811 print $user->password , "\n"; # pass1
812 print $admin->password , "\n";# pass2; inherited from User
813 print $user->hello , "\n";# I am a regular user.
814 print $admin->hello, "\n";# I am an admin.
816 ### The statement below will NOT print
817 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
818 ### The statement below will print
819 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
821 =head2 Skip row object creation for faster results
823 DBIx::Class is not built for speed, it's built for convenience and
824 ease of use, but sometimes you just need to get the data, and skip the
827 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
829 my $rs = $schema->resultset('CD');
831 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
833 my $hash_ref = $rs->find(1);
837 =head2 Get raw data for blindingly fast results
839 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
840 above is not fast enough for you, you can use a DBIx::Class to return values
841 exactly as they come out of the data base with none of the convenience methods
844 This is used like so:
846 my $cursor = $rs->cursor
847 while (my @vals = $cursor->next) {
848 # use $val[0..n] here
851 You will need to map the array offsets to particular columns (you can
852 use the I<select> attribute of C<search()> to force ordering).
854 =head1 RESULTSET OPERATIONS
856 =head2 Getting Schema from a ResultSet
858 To get the schema object from a result set, do the following:
860 $rs->result_source->schema
862 =head2 Getting Columns Of Data
866 If you want to find the sum of a particular column there are several
867 ways, the obvious one is to use search:
869 my $rs = $schema->resultset('Items')->search(
872 select => [ { sum => 'Cost' } ],
873 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
876 my $tc = $rs->first->get_column('total_cost');
878 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
879 returned when you ask the C<ResultSet> for a column using
882 my $cost = $schema->resultset('Items')->get_column('Cost');
885 With this you can also do:
887 my $minvalue = $cost->min;
888 my $maxvalue = $cost->max;
890 Or just iterate through the values of this column only:
892 while ( my $c = $cost->next ) {
896 foreach my $c ($cost->all) {
900 C<ResultSetColumn> only has a limited number of built-in functions, if
901 you need one that it doesn't have, then you can use the C<func> method
904 my $avg = $cost->func('AVERAGE');
906 This will cause the following SQL statement to be run:
908 SELECT AVERAGE(Cost) FROM Items me
910 Which will of course only work if your database supports this function.
911 See L<DBIx::Class::ResultSetColumn> for more documentation.
913 =head2 Creating a result set from a set of rows
915 Sometimes you have a (set of) row objects that you want to put into a
916 resultset without the need to hit the DB again. You can do that by using the
917 L<set_cache|DBIx::Class::Resultset/set_cache> method:
919 my @uploadable_groups;
920 while (my $group = $groups->next) {
921 if ($group->can_upload($self)) {
922 push @uploadable_groups, $group;
925 my $new_rs = $self->result_source->resultset;
926 $new_rs->set_cache(\@uploadable_groups);
930 =head1 USING RELATIONSHIPS
932 =head2 Create a new row in a related table
934 my $author = $book->create_related('author', { name => 'Fred'});
936 =head2 Search in a related table
938 Only searches for books named 'Titanic' by the author in $author.
940 my $books_rs = $author->search_related('books', { name => 'Titanic' });
942 =head2 Delete data in a related table
944 Deletes only the book named Titanic by the author in $author.
946 $author->delete_related('books', { name => 'Titanic' });
948 =head2 Ordering a relationship result set
950 If you always want a relation to be ordered, you can specify this when you
951 create the relationship.
953 To order C<< $book->pages >> by descending page_number, create the relation
956 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
958 =head2 Filtering a relationship result set
960 If you want to get a filtered result set, you can just add add to $attr as follows:
962 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
964 =head2 Many-to-many relationships
966 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
969 use base 'DBIx::Class';
970 __PACKAGE__->load_components('Core');
971 __PACKAGE__->table('user');
972 __PACKAGE__->add_columns(qw/id name/);
973 __PACKAGE__->set_primary_key('id');
974 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
975 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
977 package My::UserAddress;
978 use base 'DBIx::Class';
979 __PACKAGE__->load_components('Core');
980 __PACKAGE__->table('user_address');
981 __PACKAGE__->add_columns(qw/user address/);
982 __PACKAGE__->set_primary_key(qw/user address/);
983 __PACKAGE__->belongs_to('user' => 'My::User');
984 __PACKAGE__->belongs_to('address' => 'My::Address');
987 use base 'DBIx::Class';
988 __PACKAGE__->load_components('Core');
989 __PACKAGE__->table('address');
990 __PACKAGE__->add_columns(qw/id street town area_code country/);
991 __PACKAGE__->set_primary_key('id');
992 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
993 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
995 $rs = $user->addresses(); # get all addresses for a user
996 $rs = $address->users(); # get all users for an address
1000 As of version 0.04001, there is improved transaction support in
1001 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1002 example of the recommended way to use it:
1004 my $genus = $schema->resultset('Genus')->find(12);
1006 my $coderef2 = sub {
1011 my $coderef1 = sub {
1012 $genus->add_to_species({ name => 'troglodyte' });
1015 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1016 return $genus->species;
1021 $rs = $schema->txn_do($coderef1);
1024 if ($@) { # Transaction failed
1025 die "the sky is falling!" #
1026 if ($@ =~ /Rollback failed/); # Rollback failed
1028 deal_with_failed_transaction();
1031 Nested transactions will work as expected. That is, only the outermost
1032 transaction will actually issue a commit to the $dbh, and a rollback
1033 at any level of any transaction will cause the entire nested
1034 transaction to fail. Support for savepoints and for true nested
1035 transactions (for databases that support them) will hopefully be added
1040 =head2 Creating Schemas From An Existing Database
1042 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1043 L<DBIx::Class::Schema> and associated sources by examining the database.
1045 The recommend way of achieving this is to use the
1046 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1048 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1049 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1051 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1052 source definitions for all the tables found in the C<foo> database.
1054 =head2 Creating DDL SQL
1056 The following functionality requires you to have L<SQL::Translator>
1057 (also known as "SQL Fairy") installed.
1059 To create a set of database-specific .sql files for the above schema:
1061 my $schema = My::Schema->connect($dsn);
1062 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1067 By default this will create schema files in the current directory, for
1068 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1070 To create a new database using the schema:
1072 my $schema = My::Schema->connect($dsn);
1073 $schema->deploy({ add_drop_tables => 1});
1075 To import created .sql files using the mysql client:
1077 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1079 To create C<ALTER TABLE> conversion scripts to update a database to a
1080 newer version of your schema at a later point, first set a new
1081 C<$VERSION> in your Schema file, then:
1083 my $schema = My::Schema->connect($dsn);
1084 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1090 This will produce new database-specific .sql files for the new version
1091 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1092 requires that the files for 0.1 as created above are available in the
1093 given directory to diff against.
1095 =head2 Select from dual
1097 Dummy tables are needed by some databases to allow calling functions
1098 or expressions that aren't based on table content, for examples of how
1099 this applies to various database types, see:
1100 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1102 Note: If you're using Oracles dual table don't B<ever> do anything
1103 other than a select, if you CRUD on your dual table you *will* break
1106 Make a table class as you would for any other table
1108 package MyAppDB::Dual;
1111 use base 'DBIx::Class';
1112 __PACKAGE__->load_components("Core");
1113 __PACKAGE__->table("Dual");
1114 __PACKAGE__->add_columns(
1116 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1119 Once you've loaded your table class select from it using C<select>
1120 and C<as> instead of C<columns>
1122 my $rs = $schema->resultset('Dual')->search(undef,
1123 { select => [ 'sydate' ],
1128 All you have to do now is be careful how you access your resultset, the below
1129 will not work because there is no column called 'now' in the Dual table class
1131 while (my $dual = $rs->next) {
1132 print $dual->now."\n";
1134 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1136 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1137 your Dual class for whatever you wanted to select from dual, but that's just
1138 silly, instead use C<get_column>
1140 while (my $dual = $rs->next) {
1141 print $dual->get_column('now')."\n";
1146 my $cursor = $rs->cursor;
1147 while (my @vals = $cursor->next) {
1148 print $vals[0]."\n";
1151 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1153 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1154 while ( my $dual = $rs->next ) {
1155 print $dual->{now}."\n";
1158 Here are some example C<select> conditions to illustrate the different syntax
1159 you could use for doing stuff like
1160 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1162 # get a sequence value
1163 select => [ 'A_SEQ.nextval' ],
1165 # get create table sql
1166 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1168 # get a random num between 0 and 100
1169 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1172 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1175 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1177 # which day of the week were you born on?
1178 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1180 # select 16 rows from dual
1181 select => [ "'hello'" ],
1183 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1187 =head2 Adding Indexes And Functions To Your SQL
1189 Often you will want indexes on columns on your table to speed up searching. To
1190 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1191 class (refer to the advanced
1192 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1193 to share a hook between multiple sources):
1195 package My::Schema::Artist;
1197 __PACKAGE__->table('artist');
1198 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1200 sub sqlt_deploy_hook {
1201 my ($self, $sqlt_table) = @_;
1203 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1208 Sometimes you might want to change the index depending on the type of the
1209 database for which SQL is being generated:
1211 my ($db_type = $sqlt_table->schema->translator->producer_type)
1212 =~ s/^SQL::Translator::Producer:://;
1214 You can also add hooks to the schema level to stop certain tables being
1221 sub sqlt_deploy_hook {
1222 my ($self, $sqlt_schema) = @_;
1224 $sqlt_schema->drop_table('table_name');
1227 You could also add views, procedures or triggers to the output using
1228 L<SQL::Translator::Schema/add_view>,
1229 L<SQL::Translator::Schema/add_procedure> or
1230 L<SQL::Translator::Schema/add_trigger>.
1233 =head2 Schema versioning
1235 The following example shows simplistically how you might use DBIx::Class to
1236 deploy versioned schemas to your customers. The basic process is as follows:
1242 Create a DBIx::Class schema
1254 Modify schema to change functionality
1258 Deploy update to customers
1262 B<Create a DBIx::Class schema>
1264 This can either be done manually, or generated from an existing database as
1265 described under L</Creating Schemas From An Existing Database>
1269 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1271 B<Deploy to customers>
1273 There are several ways you could deploy your schema. These are probably
1274 beyond the scope of this recipe, but might include:
1280 Require customer to apply manually using their RDBMS.
1284 Package along with your app, making database dump/schema update/tests
1285 all part of your install.
1289 B<Modify the schema to change functionality>
1291 As your application evolves, it may be necessary to modify your schema
1292 to change functionality. Once the changes are made to your schema in
1293 DBIx::Class, export the modified schema and the conversion scripts as
1294 in L</Creating DDL SQL>.
1296 B<Deploy update to customers>
1298 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1299 Schema class. This will add a new table to your database called
1300 C<dbix_class_schema_vesion> which will keep track of which version is installed
1301 and warn if the user trys to run a newer schema version than the
1302 database thinks it has.
1304 Alternatively, you can send the conversion sql scripts to your
1307 =head2 Setting quoting for the generated SQL.
1309 If the database contains column names with spaces and/or reserved words, they
1310 need to be quoted in the SQL queries. This is done using:
1312 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1313 __PACKAGE__->storage->sql_maker->name_sep('.');
1315 The first sets the quote characters. Either a pair of matching
1316 brackets, or a C<"> or C<'>:
1318 __PACKAGE__->storage->sql_maker->quote_char('"');
1320 Check the documentation of your database for the correct quote
1321 characters to use. C<name_sep> needs to be set to allow the SQL
1322 generator to put the quotes the correct place.
1324 In most cases you should set these as part of the arguments passed to
1325 L<DBIx::Class::Schema/connect>:
1327 my $schema = My::Schema->connect(
1337 =head2 Setting limit dialect for SQL::Abstract::Limit
1339 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1340 the remote SQL server by looking at the database handle. This is a
1341 common problem when using the DBD::JDBC, since the DBD-driver only
1342 know that in has a Java-driver available, not which JDBC driver the
1343 Java component has loaded. This specifically sets the limit_dialect
1344 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1347 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1349 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1350 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1352 The limit dialect can also be set at connect time by specifying a
1353 C<limit_dialect> key in the final hash as shown above.
1355 =head2 Working with PostgreSQL array types
1357 If your SQL::Abstract version (>= 1.50) supports it, you can assign to
1358 PostgreSQL array values by passing array references in the C<\%columns>
1359 (C<\%vals>) hashref of the L<DBIx::Class::ResultSet/create> and
1360 L<DBIx::Class::Row/update> family of methods:
1362 $resultset->create({
1363 numbers => [1, 2, 3]
1368 numbers => [1, 2, 3]
1375 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1376 methods) you cannot directly use array references (since this is interpreted as
1377 a list of values to be C<OR>ed), but you can use the following syntax to force
1378 passing them as bind values:
1382 numbers => \[ '= ?', [1, 2, 3] ]
1386 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1387 placeholders and bind values (subqueries)> for more explanation.
1389 =head1 BOOTSTRAPPING/MIGRATING
1391 =head2 Easy migration from class-based to schema-based setup
1393 You want to start using the schema-based approach to L<DBIx::Class>
1394 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1395 of existing classes that you don't want to move by hand. Try this nifty script
1399 use SQL::Translator;
1401 my $schema = MyDB->schema_instance;
1403 my $translator = SQL::Translator->new(
1404 debug => $debug || 0,
1405 trace => $trace || 0,
1406 no_comments => $no_comments || 0,
1407 show_warnings => $show_warnings || 0,
1408 add_drop_table => $add_drop_table || 0,
1409 validate => $validate || 0,
1411 'DBIx::Schema' => $schema,
1414 'prefix' => 'My::Schema',
1418 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1419 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1421 my $output = $translator->translate(@args) or die
1422 "Error: " . $translator->error;
1426 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1427 namespace, which is currently left as an exercise for the reader.
1429 =head1 OVERLOADING METHODS
1431 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1432 method calls, useful for things like default values and triggers. You have to
1433 use calls to C<next::method> to overload methods. More information on using
1434 L<Class::C3> with L<DBIx::Class> can be found in
1435 L<DBIx::Class::Manual::Component>.
1437 =head2 Setting default values for a row
1439 It's as simple as overriding the C<new> method. Note the use of
1443 my ( $class, $attrs ) = @_;
1445 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1447 my $new = $class->next::method($attrs);
1452 For more information about C<next::method>, look in the L<Class::C3>
1453 documentation. See also L<DBIx::Class::Manual::Component> for more
1454 ways to write your own base classes to do this.
1456 People looking for ways to do "triggers" with DBIx::Class are probably
1457 just looking for this.
1459 =head2 Changing one field whenever another changes
1461 For example, say that you have three columns, C<id>, C<number>, and
1462 C<squared>. You would like to make changes to C<number> and have
1463 C<squared> be automagically set to the value of C<number> squared.
1464 You can accomplish this by overriding C<store_column>:
1467 my ( $self, $name, $value ) = @_;
1468 if ($name eq 'number') {
1469 $self->squared($value * $value);
1471 $self->next::method($name, $value);
1474 Note that the hard work is done by the call to C<next::method>, which
1475 redispatches your call to store_column in the superclass(es).
1477 =head2 Automatically creating related objects
1479 You might have a class C<Artist> which has many C<CD>s. Further, if you
1480 want to create a C<CD> object every time you insert an C<Artist> object.
1481 You can accomplish this by overriding C<insert> on your objects:
1484 my ( $self, @args ) = @_;
1485 $self->next::method(@args);
1486 $self->cds->new({})->fill_from_artist($self)->insert;
1490 where C<fill_from_artist> is a method you specify in C<CD> which sets
1491 values in C<CD> based on the data in the C<Artist> object you pass in.
1493 =head2 Wrapping/overloading a column accessor
1497 Say you have a table "Camera" and want to associate a description
1498 with each camera. For most cameras, you'll be able to generate the description from
1499 the other columns. However, in a few special cases you may want to associate a
1500 custom description with a camera.
1504 In your database schema, define a description field in the "Camera" table that
1505 can contain text and null values.
1507 In DBIC, we'll overload the column accessor to provide a sane default if no
1508 custom description is defined. The accessor will either return or generate the
1509 description, depending on whether the field is null or not.
1511 First, in your "Camera" schema class, define the description field as follows:
1513 __PACKAGE__->add_columns(description => { accessor => '_description' });
1515 Next, we'll define the accessor-wrapper subroutine:
1520 # If there is an update to the column, we'll let the original accessor
1522 return $self->_description(@_) if @_;
1524 # Fetch the column value.
1525 my $description = $self->_description;
1527 # If there's something in the description field, then just return that.
1528 return $description if defined $description && length $descripton;
1530 # Otherwise, generate a description.
1531 return $self->generate_description;
1534 =head1 DEBUGGING AND PROFILING
1536 =head2 DBIx::Class objects with Data::Dumper
1538 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1539 be hard to find the pertinent data in all the data it can generate.
1540 Specifically, if one naively tries to use it like so,
1544 my $cd = $schema->resultset('CD')->find(1);
1547 several pages worth of data from the CD object's schema and result source will
1548 be dumped to the screen. Since usually one is only interested in a few column
1549 values of the object, this is not very helpful.
1551 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1552 it. Simply define a hook that L<Data::Dumper> will call on the object before
1553 dumping it. For example,
1560 result_source => undef,
1568 local $Data::Dumper::Freezer = '_dumper_hook';
1570 my $cd = $schema->resultset('CD')->find(1);
1572 # dumps $cd without its ResultSource
1574 If the structure of your schema is such that there is a common base class for
1575 all your table classes, simply put a method similar to C<_dumper_hook> in the
1576 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1577 will automagically clean up your data before printing it. See
1578 L<Data::Dumper/EXAMPLES> for more information.
1582 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1583 executed as well as notifications of query completion and transaction
1584 begin/commit. If you'd like to profile the SQL you can subclass the
1585 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1588 package My::Profiler;
1591 use base 'DBIx::Class::Storage::Statistics';
1593 use Time::HiRes qw(time);
1602 $self->print("Executing $sql: ".join(', ', @params)."\n");
1611 my $elapsed = sprintf("%0.4f", time() - $start);
1612 $self->print("Execution took $elapsed seconds.\n");
1618 You can then install that class as the debugging object:
1620 __PACKAGE__->storage->debugobj(new My::Profiler());
1621 __PACKAGE__->storage->debug(1);
1623 A more complicated example might involve storing each execution of SQL in an
1631 my $elapsed = time() - $start;
1632 push(@{ $calls{$sql} }, {
1638 You could then create average, high and low execution times for an SQL
1639 statement and dig down to see if certain parameters cause aberrant behavior.
1640 You might want to check out L<DBIx::Class::QueryLog> as well.
1642 =head1 STARTUP SPEED
1644 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1645 as the ORM loads all the relevant classes. This section examines
1646 techniques for reducing the startup delay.
1648 These tips are are listed in order of decreasing effectiveness - so the
1649 first tip, if applicable, should have the greatest effect on your
1652 =head2 Statically Define Your Schema
1655 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1656 classes dynamically based on the database schema then there will be a
1657 significant startup delay.
1659 For production use a statically defined schema (which can be generated
1660 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1661 the database schema once - see
1662 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1663 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1664 details on creating static schemas from a database).
1666 =head2 Move Common Startup into a Base Class
1668 Typically L<DBIx::Class> result classes start off with
1670 use base qw/DBIx::Class/;
1671 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1673 If this preamble is moved into a common base class:-
1677 use base qw/DBIx::Class/;
1678 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1681 and each result class then uses this as a base:-
1683 use base qw/MyDBICbase/;
1685 then the load_components is only performed once, which can result in a
1686 considerable startup speedup for schemas with many classes.
1688 =head2 Explicitly List Schema Result Classes
1690 The schema class will normally contain
1692 __PACKAGE__->load_classes();
1694 to load the result classes. This will use L<Module::Find|Module::Find>
1695 to find and load the appropriate modules. Explicitly defining the
1696 classes you wish to load will remove the overhead of
1697 L<Module::Find|Module::Find> and the related directory operations:-
1699 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1701 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1702 syntax to load the appropriate classes there is not a direct alternative
1703 avoiding L<Module::Find|Module::Find>.