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->resultset('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->resultset('CD')->search({
316 artist_id => $inside_rs->get_column('id')->as_query,
319 =head3 Correlated subqueries
321 my $cdrs = $schema->resultset('CD');
322 my $rs = $cdrs->search({
324 '=' => $cdrs->search(
325 { artistid => { '=' => \'me.artistid' } },
327 )->get_column('year')->max_rs->as_query,
331 That creates the following SQL:
333 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
336 SELECT MAX(inner.year)
338 WHERE artistid = me.artistid
341 =head2 Where subqueries will work
343 Currently, subqueries will B<only> work in the where-clause of a search. In
344 other words, in the first hashref of a search() method. Work is being done
345 to make them work as part of the second hashref (from, select, +select, etc).
347 =head2 Predefined searches
349 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
350 and define often used searches as methods:
352 package My::DBIC::ResultSet::CD;
355 use base 'DBIx::Class::ResultSet';
357 sub search_cds_ordered {
360 return $self->search(
362 { order_by => 'name DESC' },
368 To use your resultset, first tell DBIx::Class to create an instance of it
369 for you, in your My::DBIC::Schema::CD class:
371 # class definition as normal
372 __PACKAGE__->load_components(qw/ Core /);
373 __PACKAGE__->table('cd');
375 # tell DBIC to use the custom ResultSet class
376 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
378 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
380 Then call your new method in your code:
382 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
384 =head2 Using SQL functions on the left hand side of a comparison
386 Using SQL functions on the left hand side of a comparison is generally
387 not a good idea since it requires a scan of the entire table. However,
388 it can be accomplished with C<DBIx::Class> when necessary.
390 If you do not have quoting on, simply include the function in your search
391 specification as you would any column:
393 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
395 With quoting on, or for a more portable solution, use the C<where>
398 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
402 (When the bind args ordering bug is fixed, this technique will be better
403 and can replace the one above.)
405 With quoting on, or for a more portable solution, use the C<where> and
409 where => \'YEAR(date_of_birth) = ?',
415 =head1 JOINS AND PREFETCHING
417 =head2 Using joins and prefetch
419 You can use the C<join> attribute to allow searching on, or sorting your
420 results by, one or more columns in a related table. To return all CDs matching
421 a particular artist name:
423 my $rs = $schema->resultset('CD')->search(
425 'artist.name' => 'Bob Marley'
428 join => 'artist', # join the artist table
433 # SELECT cd.* FROM cd
434 # JOIN artist ON cd.artist = artist.id
435 # WHERE artist.name = 'Bob Marley'
437 If required, you can now sort on any column in the related tables by including
438 it in your C<order_by> attribute:
440 my $rs = $schema->resultset('CD')->search(
442 'artist.name' => 'Bob Marley'
446 order_by => [qw/ artist.name /]
451 # SELECT cd.* FROM cd
452 # JOIN artist ON cd.artist = artist.id
453 # WHERE artist.name = 'Bob Marley'
454 # ORDER BY artist.name
456 Note that the C<join> attribute should only be used when you need to search or
457 sort using columns in a related table. Joining related tables when you only
458 need columns from the main table will make performance worse!
460 Now let's say you want to display a list of CDs, each with the name of the
461 artist. The following will work fine:
463 while (my $cd = $rs->next) {
464 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
467 There is a problem however. We have searched both the C<cd> and C<artist> tables
468 in our main query, but we have only returned data from the C<cd> table. To get
469 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
472 SELECT artist.* FROM artist WHERE artist.id = ?
474 A statement like the one above will run for each and every CD returned by our
475 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
478 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
479 This allows you to fetch results from related tables in advance:
481 my $rs = $schema->resultset('CD')->search(
483 'artist.name' => 'Bob Marley'
487 order_by => [qw/ artist.name /],
488 prefetch => 'artist' # return artist data too!
492 # Equivalent SQL (note SELECT from both "cd" and "artist"):
493 # SELECT cd.*, artist.* FROM cd
494 # JOIN artist ON cd.artist = artist.id
495 # WHERE artist.name = 'Bob Marley'
496 # ORDER BY artist.name
498 The code to print the CD list remains the same:
500 while (my $cd = $rs->next) {
501 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
504 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
505 so no additional SQL statements are executed. You now have a much more
508 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
509 C<has_many> relationships.
511 Also note that C<prefetch> should only be used when you know you will
512 definitely use data from a related table. Pre-fetching related tables when you
513 only need columns from the main table will make performance worse!
515 =head2 Multiple joins
517 In the examples above, the C<join> attribute was a scalar. If you
518 pass an array reference instead, you can join to multiple tables. In
519 this example, we want to limit the search further, using
522 # Relationships defined elsewhere:
523 # CD->belongs_to('artist' => 'Artist');
524 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
525 my $rs = $schema->resultset('CD')->search(
527 'artist.name' => 'Bob Marley'
528 'liner_notes.notes' => { 'like', '%some text%' },
531 join => [qw/ artist liner_notes /],
532 order_by => [qw/ artist.name /],
537 # SELECT cd.*, artist.*, liner_notes.* FROM cd
538 # JOIN artist ON cd.artist = artist.id
539 # JOIN liner_notes ON cd.id = liner_notes.cd
540 # WHERE artist.name = 'Bob Marley'
541 # ORDER BY artist.name
543 =head2 Multi-step joins
545 Sometimes you want to join more than one relationship deep. In this example,
546 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
547 contain a specific string:
549 # Relationships defined elsewhere:
550 # Artist->has_many('cds' => 'CD', 'artist');
551 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
553 my $rs = $schema->resultset('Artist')->search(
555 'liner_notes.notes' => { 'like', '%some text%' },
559 'cds' => 'liner_notes'
565 # SELECT artist.* FROM artist
566 # LEFT JOIN cd ON artist.id = cd.artist
567 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
568 # WHERE liner_notes.notes LIKE '%some text%'
570 Joins can be nested to an arbitrary level. So if we decide later that we
571 want to reduce the number of Artists returned based on who wrote the liner
574 # Relationship defined elsewhere:
575 # LinerNotes->belongs_to('author' => 'Person');
577 my $rs = $schema->resultset('Artist')->search(
579 'liner_notes.notes' => { 'like', '%some text%' },
580 'author.name' => 'A. Writer'
585 'liner_notes' => 'author'
592 # SELECT artist.* FROM artist
593 # LEFT JOIN cd ON artist.id = cd.artist
594 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
595 # LEFT JOIN author ON author.id = liner_notes.author
596 # WHERE liner_notes.notes LIKE '%some text%'
597 # AND author.name = 'A. Writer'
599 =head2 Multi-step and multiple joins
601 With various combinations of array and hash references, you can join
602 tables in any combination you desire. For example, to join Artist to
603 CD and Concert, and join CD to LinerNotes:
605 # Relationships defined elsewhere:
606 # Artist->has_many('concerts' => 'Concert', 'artist');
608 my $rs = $schema->resultset('Artist')->search(
621 # SELECT artist.* FROM artist
622 # LEFT JOIN cd ON artist.id = cd.artist
623 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
624 # LEFT JOIN concert ON artist.id = concert.artist
626 =head2 Multi-step prefetch
628 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
629 deep using the same syntax as a multi-step join:
631 my $rs = $schema->resultset('Tag')->search(
641 # SELECT tag.*, cd.*, artist.* FROM tag
642 # JOIN cd ON tag.cd = cd.id
643 # JOIN artist ON cd.artist = artist.id
645 Now accessing our C<cd> and C<artist> relationships does not need additional
648 my $tag = $rs->first;
649 print $tag->cd->artist->name;
651 =head1 ROW-LEVEL OPERATIONS
653 =head2 Retrieving a row object's Schema
655 It is possible to get a Schema object from a row object like so:
657 my $schema = $cd->result_source->schema;
658 # use the schema as normal:
659 my $artist_rs = $schema->resultset('Artist');
661 This can be useful when you don't want to pass around a Schema object to every
664 =head2 Getting the value of the primary key for the last database insert
666 AKA getting last_insert_id
668 If you are using PK::Auto (which is a core component as of 0.07), this is
671 my $foo = $rs->create(\%blah);
673 my $id = $foo->id; # foo->my_primary_key_field will also work.
675 If you are not using autoincrementing primary keys, this will probably
676 not work, but then you already know the value of the last primary key anyway.
678 =head2 Stringification
680 Employ the standard stringification technique by using the C<overload>
683 To make an object stringify itself as a single column, use something
684 like this (replace C<foo> with the column/method of your choice):
686 use overload '""' => sub { shift->name}, fallback => 1;
688 For more complex stringification, you can use an anonymous subroutine:
690 use overload '""' => sub { $_[0]->name . ", " .
691 $_[0]->address }, fallback => 1;
693 =head3 Stringification Example
695 Suppose we have two tables: C<Product> and C<Category>. The table
698 Product(id, Description, category)
699 Category(id, Description)
701 C<category> is a foreign key into the Category table.
703 If you have a Product object C<$obj> and write something like
707 things will not work as expected.
709 To obtain, for example, the category description, you should add this
710 method to the class defining the Category table:
712 use overload "" => sub {
715 return $self->Description;
718 =head2 Want to know if find_or_create found or created a row?
720 Just use C<find_or_new> instead, then check C<in_storage>:
722 my $obj = $rs->find_or_new({ blah => 'blarg' });
723 unless ($obj->in_storage) {
725 # do whatever else you wanted if it was a new row
728 =head2 Dynamic Sub-classing DBIx::Class proxy classes
730 AKA multi-class object inflation from one table
732 L<DBIx::Class> classes are proxy classes, therefore some different
733 techniques need to be employed for more than basic subclassing. In
734 this example we have a single user table that carries a boolean bit
735 for admin. We would like like to give the admin users
736 objects(L<DBIx::Class::Row>) the same methods as a regular user but
737 also special admin only methods. It doesn't make sense to create two
738 seperate proxy-class files for this. We would be copying all the user
739 methods into the Admin class. There is a cleaner way to accomplish
742 Overriding the C<inflate_result> method within the User proxy-class
743 gives us the effect we want. This method is called by
744 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
745 grab the object being returned, inspect the values we are looking for,
746 bless it if it's an admin object, and then return it. See the example
753 use base qw/DBIx::Class::Schema/;
755 __PACKAGE__->load_classes(qw/User/);
758 B<Proxy-Class definitions>
760 package DB::Schema::User;
764 use base qw/DBIx::Class/;
766 ### Defined what our admin class is for ensure_class_loaded
767 my $admin_class = __PACKAGE__ . '::Admin';
769 __PACKAGE__->load_components(qw/Core/);
771 __PACKAGE__->table('users');
773 __PACKAGE__->add_columns(qw/user_id email password
774 firstname lastname active
777 __PACKAGE__->set_primary_key('user_id');
781 my $ret = $self->next::method(@_);
782 if( $ret->admin ) {### If this is an admin rebless for extra functions
783 $self->ensure_class_loaded( $admin_class );
784 bless $ret, $admin_class;
790 print "I am a regular user.\n";
795 package DB::Schema::User::Admin;
799 use base qw/DB::Schema::User/;
803 print "I am an admin.\n";
809 print "I am doing admin stuff\n";
819 my $user_data = { email => 'someguy@place.com',
823 my $admin_data = { email => 'someadmin@adminplace.com',
827 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
829 $schema->resultset('User')->create( $user_data );
830 $schema->resultset('User')->create( $admin_data );
832 ### Now we search for them
833 my $user = $schema->resultset('User')->single( $user_data );
834 my $admin = $schema->resultset('User')->single( $admin_data );
836 print ref $user, "\n";
837 print ref $admin, "\n";
839 print $user->password , "\n"; # pass1
840 print $admin->password , "\n";# pass2; inherited from User
841 print $user->hello , "\n";# I am a regular user.
842 print $admin->hello, "\n";# I am an admin.
844 ### The statement below will NOT print
845 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
846 ### The statement below will print
847 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
849 =head2 Skip row object creation for faster results
851 DBIx::Class is not built for speed, it's built for convenience and
852 ease of use, but sometimes you just need to get the data, and skip the
855 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
857 my $rs = $schema->resultset('CD');
859 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
861 my $hash_ref = $rs->find(1);
865 =head2 Get raw data for blindingly fast results
867 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
868 above is not fast enough for you, you can use a DBIx::Class to return values
869 exactly as they come out of the data base with none of the convenience methods
872 This is used like so:
874 my $cursor = $rs->cursor
875 while (my @vals = $cursor->next) {
876 # use $val[0..n] here
879 You will need to map the array offsets to particular columns (you can
880 use the I<select> attribute of C<search()> to force ordering).
882 =head1 RESULTSET OPERATIONS
884 =head2 Getting Schema from a ResultSet
886 To get the schema object from a result set, do the following:
888 $rs->result_source->schema
890 =head2 Getting Columns Of Data
894 If you want to find the sum of a particular column there are several
895 ways, the obvious one is to use search:
897 my $rs = $schema->resultset('Items')->search(
900 select => [ { sum => 'Cost' } ],
901 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
904 my $tc = $rs->first->get_column('total_cost');
906 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
907 returned when you ask the C<ResultSet> for a column using
910 my $cost = $schema->resultset('Items')->get_column('Cost');
913 With this you can also do:
915 my $minvalue = $cost->min;
916 my $maxvalue = $cost->max;
918 Or just iterate through the values of this column only:
920 while ( my $c = $cost->next ) {
924 foreach my $c ($cost->all) {
928 C<ResultSetColumn> only has a limited number of built-in functions, if
929 you need one that it doesn't have, then you can use the C<func> method
932 my $avg = $cost->func('AVERAGE');
934 This will cause the following SQL statement to be run:
936 SELECT AVERAGE(Cost) FROM Items me
938 Which will of course only work if your database supports this function.
939 See L<DBIx::Class::ResultSetColumn> for more documentation.
941 =head2 Creating a result set from a set of rows
943 Sometimes you have a (set of) row objects that you want to put into a
944 resultset without the need to hit the DB again. You can do that by using the
945 L<set_cache|DBIx::Class::Resultset/set_cache> method:
947 my @uploadable_groups;
948 while (my $group = $groups->next) {
949 if ($group->can_upload($self)) {
950 push @uploadable_groups, $group;
953 my $new_rs = $self->result_source->resultset;
954 $new_rs->set_cache(\@uploadable_groups);
958 =head1 USING RELATIONSHIPS
960 =head2 Create a new row in a related table
962 my $author = $book->create_related('author', { name => 'Fred'});
964 =head2 Search in a related table
966 Only searches for books named 'Titanic' by the author in $author.
968 my $books_rs = $author->search_related('books', { name => 'Titanic' });
970 =head2 Delete data in a related table
972 Deletes only the book named Titanic by the author in $author.
974 $author->delete_related('books', { name => 'Titanic' });
976 =head2 Ordering a relationship result set
978 If you always want a relation to be ordered, you can specify this when you
979 create the relationship.
981 To order C<< $book->pages >> by descending page_number, create the relation
984 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
986 =head2 Filtering a relationship result set
988 If you want to get a filtered result set, you can just add add to $attr as follows:
990 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
992 =head2 Many-to-many relationships
994 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
997 use base 'DBIx::Class';
998 __PACKAGE__->load_components('Core');
999 __PACKAGE__->table('user');
1000 __PACKAGE__->add_columns(qw/id name/);
1001 __PACKAGE__->set_primary_key('id');
1002 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1003 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1005 package My::UserAddress;
1006 use base 'DBIx::Class';
1007 __PACKAGE__->load_components('Core');
1008 __PACKAGE__->table('user_address');
1009 __PACKAGE__->add_columns(qw/user address/);
1010 __PACKAGE__->set_primary_key(qw/user address/);
1011 __PACKAGE__->belongs_to('user' => 'My::User');
1012 __PACKAGE__->belongs_to('address' => 'My::Address');
1014 package My::Address;
1015 use base 'DBIx::Class';
1016 __PACKAGE__->load_components('Core');
1017 __PACKAGE__->table('address');
1018 __PACKAGE__->add_columns(qw/id street town area_code country/);
1019 __PACKAGE__->set_primary_key('id');
1020 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1021 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1023 $rs = $user->addresses(); # get all addresses for a user
1024 $rs = $address->users(); # get all users for an address
1028 As of version 0.04001, there is improved transaction support in
1029 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1030 example of the recommended way to use it:
1032 my $genus = $schema->resultset('Genus')->find(12);
1034 my $coderef2 = sub {
1039 my $coderef1 = sub {
1040 $genus->add_to_species({ name => 'troglodyte' });
1043 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1044 return $genus->species;
1049 $rs = $schema->txn_do($coderef1);
1052 if ($@) { # Transaction failed
1053 die "the sky is falling!" #
1054 if ($@ =~ /Rollback failed/); # Rollback failed
1056 deal_with_failed_transaction();
1059 Nested transactions will work as expected. That is, only the outermost
1060 transaction will actually issue a commit to the $dbh, and a rollback
1061 at any level of any transaction will cause the entire nested
1062 transaction to fail. Support for savepoints and for true nested
1063 transactions (for databases that support them) will hopefully be added
1068 =head2 Creating Schemas From An Existing Database
1070 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1071 L<DBIx::Class::Schema> and associated sources by examining the database.
1073 The recommend way of achieving this is to use the
1074 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1076 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1077 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1079 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1080 source definitions for all the tables found in the C<foo> database.
1082 =head2 Creating DDL SQL
1084 The following functionality requires you to have L<SQL::Translator>
1085 (also known as "SQL Fairy") installed.
1087 To create a set of database-specific .sql files for the above schema:
1089 my $schema = My::Schema->connect($dsn);
1090 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1095 By default this will create schema files in the current directory, for
1096 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1098 To create a new database using the schema:
1100 my $schema = My::Schema->connect($dsn);
1101 $schema->deploy({ add_drop_tables => 1});
1103 To import created .sql files using the mysql client:
1105 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1107 To create C<ALTER TABLE> conversion scripts to update a database to a
1108 newer version of your schema at a later point, first set a new
1109 C<$VERSION> in your Schema file, then:
1111 my $schema = My::Schema->connect($dsn);
1112 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1118 This will produce new database-specific .sql files for the new version
1119 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1120 requires that the files for 0.1 as created above are available in the
1121 given directory to diff against.
1123 =head2 Select from dual
1125 Dummy tables are needed by some databases to allow calling functions
1126 or expressions that aren't based on table content, for examples of how
1127 this applies to various database types, see:
1128 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1130 Note: If you're using Oracles dual table don't B<ever> do anything
1131 other than a select, if you CRUD on your dual table you *will* break
1134 Make a table class as you would for any other table
1136 package MyAppDB::Dual;
1139 use base 'DBIx::Class';
1140 __PACKAGE__->load_components("Core");
1141 __PACKAGE__->table("Dual");
1142 __PACKAGE__->add_columns(
1144 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1147 Once you've loaded your table class select from it using C<select>
1148 and C<as> instead of C<columns>
1150 my $rs = $schema->resultset('Dual')->search(undef,
1151 { select => [ 'sydate' ],
1156 All you have to do now is be careful how you access your resultset, the below
1157 will not work because there is no column called 'now' in the Dual table class
1159 while (my $dual = $rs->next) {
1160 print $dual->now."\n";
1162 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1164 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1165 your Dual class for whatever you wanted to select from dual, but that's just
1166 silly, instead use C<get_column>
1168 while (my $dual = $rs->next) {
1169 print $dual->get_column('now')."\n";
1174 my $cursor = $rs->cursor;
1175 while (my @vals = $cursor->next) {
1176 print $vals[0]."\n";
1179 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1181 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1182 while ( my $dual = $rs->next ) {
1183 print $dual->{now}."\n";
1186 Here are some example C<select> conditions to illustrate the different syntax
1187 you could use for doing stuff like
1188 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1190 # get a sequence value
1191 select => [ 'A_SEQ.nextval' ],
1193 # get create table sql
1194 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1196 # get a random num between 0 and 100
1197 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1200 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1203 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1205 # which day of the week were you born on?
1206 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1208 # select 16 rows from dual
1209 select => [ "'hello'" ],
1211 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1215 =head2 Adding Indexes And Functions To Your SQL
1217 Often you will want indexes on columns on your table to speed up searching. To
1218 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1219 class (refer to the advanced
1220 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1221 to share a hook between multiple sources):
1223 package My::Schema::Artist;
1225 __PACKAGE__->table('artist');
1226 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1228 sub sqlt_deploy_hook {
1229 my ($self, $sqlt_table) = @_;
1231 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1236 Sometimes you might want to change the index depending on the type of the
1237 database for which SQL is being generated:
1239 my ($db_type = $sqlt_table->schema->translator->producer_type)
1240 =~ s/^SQL::Translator::Producer:://;
1242 You can also add hooks to the schema level to stop certain tables being
1249 sub sqlt_deploy_hook {
1250 my ($self, $sqlt_schema) = @_;
1252 $sqlt_schema->drop_table('table_name');
1255 You could also add views, procedures or triggers to the output using
1256 L<SQL::Translator::Schema/add_view>,
1257 L<SQL::Translator::Schema/add_procedure> or
1258 L<SQL::Translator::Schema/add_trigger>.
1261 =head2 Schema versioning
1263 The following example shows simplistically how you might use DBIx::Class to
1264 deploy versioned schemas to your customers. The basic process is as follows:
1270 Create a DBIx::Class schema
1282 Modify schema to change functionality
1286 Deploy update to customers
1290 B<Create a DBIx::Class schema>
1292 This can either be done manually, or generated from an existing database as
1293 described under L</Creating Schemas From An Existing Database>
1297 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1299 B<Deploy to customers>
1301 There are several ways you could deploy your schema. These are probably
1302 beyond the scope of this recipe, but might include:
1308 Require customer to apply manually using their RDBMS.
1312 Package along with your app, making database dump/schema update/tests
1313 all part of your install.
1317 B<Modify the schema to change functionality>
1319 As your application evolves, it may be necessary to modify your schema
1320 to change functionality. Once the changes are made to your schema in
1321 DBIx::Class, export the modified schema and the conversion scripts as
1322 in L</Creating DDL SQL>.
1324 B<Deploy update to customers>
1326 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1327 Schema class. This will add a new table to your database called
1328 C<dbix_class_schema_vesion> which will keep track of which version is installed
1329 and warn if the user trys to run a newer schema version than the
1330 database thinks it has.
1332 Alternatively, you can send the conversion sql scripts to your
1335 =head2 Setting quoting for the generated SQL.
1337 If the database contains column names with spaces and/or reserved words, they
1338 need to be quoted in the SQL queries. This is done using:
1340 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1341 __PACKAGE__->storage->sql_maker->name_sep('.');
1343 The first sets the quote characters. Either a pair of matching
1344 brackets, or a C<"> or C<'>:
1346 __PACKAGE__->storage->sql_maker->quote_char('"');
1348 Check the documentation of your database for the correct quote
1349 characters to use. C<name_sep> needs to be set to allow the SQL
1350 generator to put the quotes the correct place.
1352 In most cases you should set these as part of the arguments passed to
1353 L<DBIx::Class::Schema/connect>:
1355 my $schema = My::Schema->connect(
1365 =head2 Setting limit dialect for SQL::Abstract::Limit
1367 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1368 the remote SQL server by looking at the database handle. This is a
1369 common problem when using the DBD::JDBC, since the DBD-driver only
1370 know that in has a Java-driver available, not which JDBC driver the
1371 Java component has loaded. This specifically sets the limit_dialect
1372 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1375 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1377 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1378 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1380 The limit dialect can also be set at connect time by specifying a
1381 C<limit_dialect> key in the final hash as shown above.
1383 =head2 Working with PostgreSQL array types
1385 If your SQL::Abstract version (>= 1.50) supports it, you can assign to
1386 PostgreSQL array values by passing array references in the C<\%columns>
1387 (C<\%vals>) hashref of the L<DBIx::Class::ResultSet/create> and
1388 L<DBIx::Class::Row/update> family of methods:
1390 $resultset->create({
1391 numbers => [1, 2, 3]
1396 numbers => [1, 2, 3]
1403 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1404 methods) you cannot directly use array references (since this is interpreted as
1405 a list of values to be C<OR>ed), but you can use the following syntax to force
1406 passing them as bind values:
1410 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1414 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1415 placeholders and bind values (subqueries)> for more explanation. Note that
1416 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1417 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1418 arrayrefs together with the column name, like this: C<< [column_name => value]
1421 =head1 BOOTSTRAPPING/MIGRATING
1423 =head2 Easy migration from class-based to schema-based setup
1425 You want to start using the schema-based approach to L<DBIx::Class>
1426 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1427 of existing classes that you don't want to move by hand. Try this nifty script
1431 use SQL::Translator;
1433 my $schema = MyDB->schema_instance;
1435 my $translator = SQL::Translator->new(
1436 debug => $debug || 0,
1437 trace => $trace || 0,
1438 no_comments => $no_comments || 0,
1439 show_warnings => $show_warnings || 0,
1440 add_drop_table => $add_drop_table || 0,
1441 validate => $validate || 0,
1443 'DBIx::Schema' => $schema,
1446 'prefix' => 'My::Schema',
1450 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1451 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1453 my $output = $translator->translate(@args) or die
1454 "Error: " . $translator->error;
1458 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1459 namespace, which is currently left as an exercise for the reader.
1461 =head1 OVERLOADING METHODS
1463 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1464 method calls, useful for things like default values and triggers. You have to
1465 use calls to C<next::method> to overload methods. More information on using
1466 L<Class::C3> with L<DBIx::Class> can be found in
1467 L<DBIx::Class::Manual::Component>.
1469 =head2 Setting default values for a row
1471 It's as simple as overriding the C<new> method. Note the use of
1475 my ( $class, $attrs ) = @_;
1477 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1479 my $new = $class->next::method($attrs);
1484 For more information about C<next::method>, look in the L<Class::C3>
1485 documentation. See also L<DBIx::Class::Manual::Component> for more
1486 ways to write your own base classes to do this.
1488 People looking for ways to do "triggers" with DBIx::Class are probably
1489 just looking for this.
1491 =head2 Changing one field whenever another changes
1493 For example, say that you have three columns, C<id>, C<number>, and
1494 C<squared>. You would like to make changes to C<number> and have
1495 C<squared> be automagically set to the value of C<number> squared.
1496 You can accomplish this by overriding C<store_column>:
1499 my ( $self, $name, $value ) = @_;
1500 if ($name eq 'number') {
1501 $self->squared($value * $value);
1503 $self->next::method($name, $value);
1506 Note that the hard work is done by the call to C<next::method>, which
1507 redispatches your call to store_column in the superclass(es).
1509 =head2 Automatically creating related objects
1511 You might have a class C<Artist> which has many C<CD>s. Further, if you
1512 want to create a C<CD> object every time you insert an C<Artist> object.
1513 You can accomplish this by overriding C<insert> on your objects:
1516 my ( $self, @args ) = @_;
1517 $self->next::method(@args);
1518 $self->cds->new({})->fill_from_artist($self)->insert;
1522 where C<fill_from_artist> is a method you specify in C<CD> which sets
1523 values in C<CD> based on the data in the C<Artist> object you pass in.
1525 =head2 Wrapping/overloading a column accessor
1529 Say you have a table "Camera" and want to associate a description
1530 with each camera. For most cameras, you'll be able to generate the description from
1531 the other columns. However, in a few special cases you may want to associate a
1532 custom description with a camera.
1536 In your database schema, define a description field in the "Camera" table that
1537 can contain text and null values.
1539 In DBIC, we'll overload the column accessor to provide a sane default if no
1540 custom description is defined. The accessor will either return or generate the
1541 description, depending on whether the field is null or not.
1543 First, in your "Camera" schema class, define the description field as follows:
1545 __PACKAGE__->add_columns(description => { accessor => '_description' });
1547 Next, we'll define the accessor-wrapper subroutine:
1552 # If there is an update to the column, we'll let the original accessor
1554 return $self->_description(@_) if @_;
1556 # Fetch the column value.
1557 my $description = $self->_description;
1559 # If there's something in the description field, then just return that.
1560 return $description if defined $description && length $descripton;
1562 # Otherwise, generate a description.
1563 return $self->generate_description;
1566 =head1 DEBUGGING AND PROFILING
1568 =head2 DBIx::Class objects with Data::Dumper
1570 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1571 be hard to find the pertinent data in all the data it can generate.
1572 Specifically, if one naively tries to use it like so,
1576 my $cd = $schema->resultset('CD')->find(1);
1579 several pages worth of data from the CD object's schema and result source will
1580 be dumped to the screen. Since usually one is only interested in a few column
1581 values of the object, this is not very helpful.
1583 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1584 it. Simply define a hook that L<Data::Dumper> will call on the object before
1585 dumping it. For example,
1592 result_source => undef,
1600 local $Data::Dumper::Freezer = '_dumper_hook';
1602 my $cd = $schema->resultset('CD')->find(1);
1604 # dumps $cd without its ResultSource
1606 If the structure of your schema is such that there is a common base class for
1607 all your table classes, simply put a method similar to C<_dumper_hook> in the
1608 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1609 will automagically clean up your data before printing it. See
1610 L<Data::Dumper/EXAMPLES> for more information.
1614 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1615 executed as well as notifications of query completion and transaction
1616 begin/commit. If you'd like to profile the SQL you can subclass the
1617 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1620 package My::Profiler;
1623 use base 'DBIx::Class::Storage::Statistics';
1625 use Time::HiRes qw(time);
1634 $self->print("Executing $sql: ".join(', ', @params)."\n");
1643 my $elapsed = sprintf("%0.4f", time() - $start);
1644 $self->print("Execution took $elapsed seconds.\n");
1650 You can then install that class as the debugging object:
1652 __PACKAGE__->storage->debugobj(new My::Profiler());
1653 __PACKAGE__->storage->debug(1);
1655 A more complicated example might involve storing each execution of SQL in an
1663 my $elapsed = time() - $start;
1664 push(@{ $calls{$sql} }, {
1670 You could then create average, high and low execution times for an SQL
1671 statement and dig down to see if certain parameters cause aberrant behavior.
1672 You might want to check out L<DBIx::Class::QueryLog> as well.
1674 =head1 STARTUP SPEED
1676 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1677 as the ORM loads all the relevant classes. This section examines
1678 techniques for reducing the startup delay.
1680 These tips are are listed in order of decreasing effectiveness - so the
1681 first tip, if applicable, should have the greatest effect on your
1684 =head2 Statically Define Your Schema
1687 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1688 classes dynamically based on the database schema then there will be a
1689 significant startup delay.
1691 For production use a statically defined schema (which can be generated
1692 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1693 the database schema once - see
1694 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1695 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1696 details on creating static schemas from a database).
1698 =head2 Move Common Startup into a Base Class
1700 Typically L<DBIx::Class> result classes start off with
1702 use base qw/DBIx::Class/;
1703 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1705 If this preamble is moved into a common base class:-
1709 use base qw/DBIx::Class/;
1710 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1713 and each result class then uses this as a base:-
1715 use base qw/MyDBICbase/;
1717 then the load_components is only performed once, which can result in a
1718 considerable startup speedup for schemas with many classes.
1720 =head2 Explicitly List Schema Result Classes
1722 The schema class will normally contain
1724 __PACKAGE__->load_classes();
1726 to load the result classes. This will use L<Module::Find|Module::Find>
1727 to find and load the appropriate modules. Explicitly defining the
1728 classes you wish to load will remove the overhead of
1729 L<Module::Find|Module::Find> and the related directory operations:-
1731 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1733 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1734 syntax to load the appropriate classes there is not a direct alternative
1735 avoiding L<Module::Find|Module::Find>.