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 >).
298 =head2 Subqueries (EXPERIMENTAL)
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,
321 Subqueries are supported in the where clause (first hashref), and in the
322 from, select, and +select attributes.
324 =head3 Correlated subqueries
326 my $cdrs = $schema->resultset('CD');
327 my $rs = $cdrs->search({
329 '=' => $cdrs->search(
330 { artistid => { '=' => \'me.artistid' } },
332 )->get_column('year')->max_rs->as_query,
336 That creates the following SQL:
338 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
341 SELECT MAX(inner.year)
343 WHERE artistid = me.artistid
348 Please note that subqueries are considered an experimental feature.
350 =head2 Predefined searches
352 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
353 and define often used searches as methods:
355 package My::DBIC::ResultSet::CD;
358 use base 'DBIx::Class::ResultSet';
360 sub search_cds_ordered {
363 return $self->search(
365 { order_by => 'name DESC' },
371 To use your resultset, first tell DBIx::Class to create an instance of it
372 for you, in your My::DBIC::Schema::CD class:
374 # class definition as normal
375 __PACKAGE__->load_components(qw/ Core /);
376 __PACKAGE__->table('cd');
378 # tell DBIC to use the custom ResultSet class
379 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
381 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
383 Then call your new method in your code:
385 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
387 =head2 Using SQL functions on the left hand side of a comparison
389 Using SQL functions on the left hand side of a comparison is generally
390 not a good idea since it requires a scan of the entire table. However,
391 it can be accomplished with C<DBIx::Class> when necessary.
393 If you do not have quoting on, simply include the function in your search
394 specification as you would any column:
396 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
398 With quoting on, or for a more portable solution, use the C<where>
401 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
405 (When the bind args ordering bug is fixed, this technique will be better
406 and can replace the one above.)
408 With quoting on, or for a more portable solution, use the C<where> and
412 where => \'YEAR(date_of_birth) = ?',
418 =head1 JOINS AND PREFETCHING
420 =head2 Using joins and prefetch
422 You can use the C<join> attribute to allow searching on, or sorting your
423 results by, one or more columns in a related table. To return all CDs matching
424 a particular artist name:
426 my $rs = $schema->resultset('CD')->search(
428 'artist.name' => 'Bob Marley'
431 join => 'artist', # join the artist table
436 # SELECT cd.* FROM cd
437 # JOIN artist ON cd.artist = artist.id
438 # WHERE artist.name = 'Bob Marley'
440 If required, you can now sort on any column in the related tables by including
441 it in your C<order_by> attribute:
443 my $rs = $schema->resultset('CD')->search(
445 'artist.name' => 'Bob Marley'
449 order_by => [qw/ artist.name /]
454 # SELECT cd.* FROM cd
455 # JOIN artist ON cd.artist = artist.id
456 # WHERE artist.name = 'Bob Marley'
457 # ORDER BY artist.name
459 Note that the C<join> attribute should only be used when you need to search or
460 sort using columns in a related table. Joining related tables when you only
461 need columns from the main table will make performance worse!
463 Now let's say you want to display a list of CDs, each with the name of the
464 artist. The following will work fine:
466 while (my $cd = $rs->next) {
467 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
470 There is a problem however. We have searched both the C<cd> and C<artist> tables
471 in our main query, but we have only returned data from the C<cd> table. To get
472 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
475 SELECT artist.* FROM artist WHERE artist.id = ?
477 A statement like the one above will run for each and every CD returned by our
478 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
481 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
482 This allows you to fetch results from related tables in advance:
484 my $rs = $schema->resultset('CD')->search(
486 'artist.name' => 'Bob Marley'
490 order_by => [qw/ artist.name /],
491 prefetch => 'artist' # return artist data too!
495 # Equivalent SQL (note SELECT from both "cd" and "artist"):
496 # SELECT cd.*, artist.* FROM cd
497 # JOIN artist ON cd.artist = artist.id
498 # WHERE artist.name = 'Bob Marley'
499 # ORDER BY artist.name
501 The code to print the CD list remains the same:
503 while (my $cd = $rs->next) {
504 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
507 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
508 so no additional SQL statements are executed. You now have a much more
511 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
512 C<has_many> relationships.
514 Also note that C<prefetch> should only be used when you know you will
515 definitely use data from a related table. Pre-fetching related tables when you
516 only need columns from the main table will make performance worse!
518 =head2 Multiple joins
520 In the examples above, the C<join> attribute was a scalar. If you
521 pass an array reference instead, you can join to multiple tables. In
522 this example, we want to limit the search further, using
525 # Relationships defined elsewhere:
526 # CD->belongs_to('artist' => 'Artist');
527 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
528 my $rs = $schema->resultset('CD')->search(
530 'artist.name' => 'Bob Marley'
531 'liner_notes.notes' => { 'like', '%some text%' },
534 join => [qw/ artist liner_notes /],
535 order_by => [qw/ artist.name /],
540 # SELECT cd.*, artist.*, liner_notes.* FROM cd
541 # JOIN artist ON cd.artist = artist.id
542 # JOIN liner_notes ON cd.id = liner_notes.cd
543 # WHERE artist.name = 'Bob Marley'
544 # ORDER BY artist.name
546 =head2 Multi-step joins
548 Sometimes you want to join more than one relationship deep. In this example,
549 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
550 contain a specific string:
552 # Relationships defined elsewhere:
553 # Artist->has_many('cds' => 'CD', 'artist');
554 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
556 my $rs = $schema->resultset('Artist')->search(
558 'liner_notes.notes' => { 'like', '%some text%' },
562 'cds' => 'liner_notes'
568 # SELECT artist.* FROM artist
569 # LEFT JOIN cd ON artist.id = cd.artist
570 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
571 # WHERE liner_notes.notes LIKE '%some text%'
573 Joins can be nested to an arbitrary level. So if we decide later that we
574 want to reduce the number of Artists returned based on who wrote the liner
577 # Relationship defined elsewhere:
578 # LinerNotes->belongs_to('author' => 'Person');
580 my $rs = $schema->resultset('Artist')->search(
582 'liner_notes.notes' => { 'like', '%some text%' },
583 'author.name' => 'A. Writer'
588 'liner_notes' => 'author'
595 # SELECT artist.* FROM artist
596 # LEFT JOIN cd ON artist.id = cd.artist
597 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
598 # LEFT JOIN author ON author.id = liner_notes.author
599 # WHERE liner_notes.notes LIKE '%some text%'
600 # AND author.name = 'A. Writer'
602 =head2 Multi-step and multiple joins
604 With various combinations of array and hash references, you can join
605 tables in any combination you desire. For example, to join Artist to
606 CD and Concert, and join CD to LinerNotes:
608 # Relationships defined elsewhere:
609 # Artist->has_many('concerts' => 'Concert', 'artist');
611 my $rs = $schema->resultset('Artist')->search(
624 # SELECT artist.* FROM artist
625 # LEFT JOIN cd ON artist.id = cd.artist
626 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
627 # LEFT JOIN concert ON artist.id = concert.artist
629 =head2 Multi-step prefetch
631 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
632 deep using the same syntax as a multi-step join:
634 my $rs = $schema->resultset('Tag')->search(
644 # SELECT tag.*, cd.*, artist.* FROM tag
645 # JOIN cd ON tag.cd = cd.id
646 # JOIN artist ON cd.artist = artist.id
648 Now accessing our C<cd> and C<artist> relationships does not need additional
651 my $tag = $rs->first;
652 print $tag->cd->artist->name;
654 =head1 ROW-LEVEL OPERATIONS
656 =head2 Retrieving a row object's Schema
658 It is possible to get a Schema object from a row object like so:
660 my $schema = $cd->result_source->schema;
661 # use the schema as normal:
662 my $artist_rs = $schema->resultset('Artist');
664 This can be useful when you don't want to pass around a Schema object to every
667 =head2 Getting the value of the primary key for the last database insert
669 AKA getting last_insert_id
671 If you are using PK::Auto (which is a core component as of 0.07), this is
674 my $foo = $rs->create(\%blah);
676 my $id = $foo->id; # foo->my_primary_key_field will also work.
678 If you are not using autoincrementing primary keys, this will probably
679 not work, but then you already know the value of the last primary key anyway.
681 =head2 Stringification
683 Employ the standard stringification technique by using the C<overload>
686 To make an object stringify itself as a single column, use something
687 like this (replace C<foo> with the column/method of your choice):
689 use overload '""' => sub { shift->name}, fallback => 1;
691 For more complex stringification, you can use an anonymous subroutine:
693 use overload '""' => sub { $_[0]->name . ", " .
694 $_[0]->address }, fallback => 1;
696 =head3 Stringification Example
698 Suppose we have two tables: C<Product> and C<Category>. The table
701 Product(id, Description, category)
702 Category(id, Description)
704 C<category> is a foreign key into the Category table.
706 If you have a Product object C<$obj> and write something like
710 things will not work as expected.
712 To obtain, for example, the category description, you should add this
713 method to the class defining the Category table:
715 use overload "" => sub {
718 return $self->Description;
721 =head2 Want to know if find_or_create found or created a row?
723 Just use C<find_or_new> instead, then check C<in_storage>:
725 my $obj = $rs->find_or_new({ blah => 'blarg' });
726 unless ($obj->in_storage) {
728 # do whatever else you wanted if it was a new row
731 =head2 Dynamic Sub-classing DBIx::Class proxy classes
733 AKA multi-class object inflation from one table
735 L<DBIx::Class> classes are proxy classes, therefore some different
736 techniques need to be employed for more than basic subclassing. In
737 this example we have a single user table that carries a boolean bit
738 for admin. We would like like to give the admin users
739 objects(L<DBIx::Class::Row>) the same methods as a regular user but
740 also special admin only methods. It doesn't make sense to create two
741 seperate proxy-class files for this. We would be copying all the user
742 methods into the Admin class. There is a cleaner way to accomplish
745 Overriding the C<inflate_result> method within the User proxy-class
746 gives us the effect we want. This method is called by
747 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
748 grab the object being returned, inspect the values we are looking for,
749 bless it if it's an admin object, and then return it. See the example
756 use base qw/DBIx::Class::Schema/;
758 __PACKAGE__->load_classes(qw/User/);
761 B<Proxy-Class definitions>
763 package DB::Schema::User;
767 use base qw/DBIx::Class/;
769 ### Defined what our admin class is for ensure_class_loaded
770 my $admin_class = __PACKAGE__ . '::Admin';
772 __PACKAGE__->load_components(qw/Core/);
774 __PACKAGE__->table('users');
776 __PACKAGE__->add_columns(qw/user_id email password
777 firstname lastname active
780 __PACKAGE__->set_primary_key('user_id');
784 my $ret = $self->next::method(@_);
785 if( $ret->admin ) {### If this is an admin rebless for extra functions
786 $self->ensure_class_loaded( $admin_class );
787 bless $ret, $admin_class;
793 print "I am a regular user.\n";
798 package DB::Schema::User::Admin;
802 use base qw/DB::Schema::User/;
806 print "I am an admin.\n";
812 print "I am doing admin stuff\n";
822 my $user_data = { email => 'someguy@place.com',
826 my $admin_data = { email => 'someadmin@adminplace.com',
830 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
832 $schema->resultset('User')->create( $user_data );
833 $schema->resultset('User')->create( $admin_data );
835 ### Now we search for them
836 my $user = $schema->resultset('User')->single( $user_data );
837 my $admin = $schema->resultset('User')->single( $admin_data );
839 print ref $user, "\n";
840 print ref $admin, "\n";
842 print $user->password , "\n"; # pass1
843 print $admin->password , "\n";# pass2; inherited from User
844 print $user->hello , "\n";# I am a regular user.
845 print $admin->hello, "\n";# I am an admin.
847 ### The statement below will NOT print
848 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
849 ### The statement below will print
850 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
852 =head2 Skip row object creation for faster results
854 DBIx::Class is not built for speed, it's built for convenience and
855 ease of use, but sometimes you just need to get the data, and skip the
858 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
860 my $rs = $schema->resultset('CD');
862 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
864 my $hash_ref = $rs->find(1);
868 =head2 Get raw data for blindingly fast results
870 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
871 above is not fast enough for you, you can use a DBIx::Class to return values
872 exactly as they come out of the data base with none of the convenience methods
875 This is used like so:
877 my $cursor = $rs->cursor
878 while (my @vals = $cursor->next) {
879 # use $val[0..n] here
882 You will need to map the array offsets to particular columns (you can
883 use the I<select> attribute of C<search()> to force ordering).
885 =head1 RESULTSET OPERATIONS
887 =head2 Getting Schema from a ResultSet
889 To get the schema object from a result set, do the following:
891 $rs->result_source->schema
893 =head2 Getting Columns Of Data
897 If you want to find the sum of a particular column there are several
898 ways, the obvious one is to use search:
900 my $rs = $schema->resultset('Items')->search(
903 select => [ { sum => 'Cost' } ],
904 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
907 my $tc = $rs->first->get_column('total_cost');
909 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
910 returned when you ask the C<ResultSet> for a column using
913 my $cost = $schema->resultset('Items')->get_column('Cost');
916 With this you can also do:
918 my $minvalue = $cost->min;
919 my $maxvalue = $cost->max;
921 Or just iterate through the values of this column only:
923 while ( my $c = $cost->next ) {
927 foreach my $c ($cost->all) {
931 C<ResultSetColumn> only has a limited number of built-in functions, if
932 you need one that it doesn't have, then you can use the C<func> method
935 my $avg = $cost->func('AVERAGE');
937 This will cause the following SQL statement to be run:
939 SELECT AVERAGE(Cost) FROM Items me
941 Which will of course only work if your database supports this function.
942 See L<DBIx::Class::ResultSetColumn> for more documentation.
944 =head2 Creating a result set from a set of rows
946 Sometimes you have a (set of) row objects that you want to put into a
947 resultset without the need to hit the DB again. You can do that by using the
948 L<set_cache|DBIx::Class::Resultset/set_cache> method:
950 my @uploadable_groups;
951 while (my $group = $groups->next) {
952 if ($group->can_upload($self)) {
953 push @uploadable_groups, $group;
956 my $new_rs = $self->result_source->resultset;
957 $new_rs->set_cache(\@uploadable_groups);
961 =head1 USING RELATIONSHIPS
963 =head2 Create a new row in a related table
965 my $author = $book->create_related('author', { name => 'Fred'});
967 =head2 Search in a related table
969 Only searches for books named 'Titanic' by the author in $author.
971 my $books_rs = $author->search_related('books', { name => 'Titanic' });
973 =head2 Delete data in a related table
975 Deletes only the book named Titanic by the author in $author.
977 $author->delete_related('books', { name => 'Titanic' });
979 =head2 Ordering a relationship result set
981 If you always want a relation to be ordered, you can specify this when you
982 create the relationship.
984 To order C<< $book->pages >> by descending page_number, create the relation
987 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
989 =head2 Filtering a relationship result set
991 If you want to get a filtered result set, you can just add add to $attr as follows:
993 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
995 =head2 Many-to-many relationships
997 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1000 use base 'DBIx::Class';
1001 __PACKAGE__->load_components('Core');
1002 __PACKAGE__->table('user');
1003 __PACKAGE__->add_columns(qw/id name/);
1004 __PACKAGE__->set_primary_key('id');
1005 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1006 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1008 package My::UserAddress;
1009 use base 'DBIx::Class';
1010 __PACKAGE__->load_components('Core');
1011 __PACKAGE__->table('user_address');
1012 __PACKAGE__->add_columns(qw/user address/);
1013 __PACKAGE__->set_primary_key(qw/user address/);
1014 __PACKAGE__->belongs_to('user' => 'My::User');
1015 __PACKAGE__->belongs_to('address' => 'My::Address');
1017 package My::Address;
1018 use base 'DBIx::Class';
1019 __PACKAGE__->load_components('Core');
1020 __PACKAGE__->table('address');
1021 __PACKAGE__->add_columns(qw/id street town area_code country/);
1022 __PACKAGE__->set_primary_key('id');
1023 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1024 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1026 $rs = $user->addresses(); # get all addresses for a user
1027 $rs = $address->users(); # get all users for an address
1031 As of version 0.04001, there is improved transaction support in
1032 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1033 example of the recommended way to use it:
1035 my $genus = $schema->resultset('Genus')->find(12);
1037 my $coderef2 = sub {
1042 my $coderef1 = sub {
1043 $genus->add_to_species({ name => 'troglodyte' });
1046 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1047 return $genus->species;
1052 $rs = $schema->txn_do($coderef1);
1055 if ($@) { # Transaction failed
1056 die "the sky is falling!" #
1057 if ($@ =~ /Rollback failed/); # Rollback failed
1059 deal_with_failed_transaction();
1062 Nested transactions will work as expected. That is, only the outermost
1063 transaction will actually issue a commit to the $dbh, and a rollback
1064 at any level of any transaction will cause the entire nested
1065 transaction to fail. Support for savepoints and for true nested
1066 transactions (for databases that support them) will hopefully be added
1071 =head2 Creating Schemas From An Existing Database
1073 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1074 L<DBIx::Class::Schema> and associated sources by examining the database.
1076 The recommend way of achieving this is to use the
1077 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1079 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1080 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1082 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1083 source definitions for all the tables found in the C<foo> database.
1085 =head2 Creating DDL SQL
1087 The following functionality requires you to have L<SQL::Translator>
1088 (also known as "SQL Fairy") installed.
1090 To create a set of database-specific .sql files for the above schema:
1092 my $schema = My::Schema->connect($dsn);
1093 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1098 By default this will create schema files in the current directory, for
1099 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1101 To create a new database using the schema:
1103 my $schema = My::Schema->connect($dsn);
1104 $schema->deploy({ add_drop_tables => 1});
1106 To import created .sql files using the mysql client:
1108 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1110 To create C<ALTER TABLE> conversion scripts to update a database to a
1111 newer version of your schema at a later point, first set a new
1112 C<$VERSION> in your Schema file, then:
1114 my $schema = My::Schema->connect($dsn);
1115 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1121 This will produce new database-specific .sql files for the new version
1122 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1123 requires that the files for 0.1 as created above are available in the
1124 given directory to diff against.
1126 =head2 Select from dual
1128 Dummy tables are needed by some databases to allow calling functions
1129 or expressions that aren't based on table content, for examples of how
1130 this applies to various database types, see:
1131 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1133 Note: If you're using Oracles dual table don't B<ever> do anything
1134 other than a select, if you CRUD on your dual table you *will* break
1137 Make a table class as you would for any other table
1139 package MyAppDB::Dual;
1142 use base 'DBIx::Class';
1143 __PACKAGE__->load_components("Core");
1144 __PACKAGE__->table("Dual");
1145 __PACKAGE__->add_columns(
1147 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1150 Once you've loaded your table class select from it using C<select>
1151 and C<as> instead of C<columns>
1153 my $rs = $schema->resultset('Dual')->search(undef,
1154 { select => [ 'sydate' ],
1159 All you have to do now is be careful how you access your resultset, the below
1160 will not work because there is no column called 'now' in the Dual table class
1162 while (my $dual = $rs->next) {
1163 print $dual->now."\n";
1165 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1167 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1168 your Dual class for whatever you wanted to select from dual, but that's just
1169 silly, instead use C<get_column>
1171 while (my $dual = $rs->next) {
1172 print $dual->get_column('now')."\n";
1177 my $cursor = $rs->cursor;
1178 while (my @vals = $cursor->next) {
1179 print $vals[0]."\n";
1182 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1184 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1185 while ( my $dual = $rs->next ) {
1186 print $dual->{now}."\n";
1189 Here are some example C<select> conditions to illustrate the different syntax
1190 you could use for doing stuff like
1191 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1193 # get a sequence value
1194 select => [ 'A_SEQ.nextval' ],
1196 # get create table sql
1197 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1199 # get a random num between 0 and 100
1200 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1203 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1206 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1208 # which day of the week were you born on?
1209 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1211 # select 16 rows from dual
1212 select => [ "'hello'" ],
1214 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1218 =head2 Adding Indexes And Functions To Your SQL
1220 Often you will want indexes on columns on your table to speed up searching. To
1221 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1222 class (refer to the advanced
1223 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1224 to share a hook between multiple sources):
1226 package My::Schema::Artist;
1228 __PACKAGE__->table('artist');
1229 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1231 sub sqlt_deploy_hook {
1232 my ($self, $sqlt_table) = @_;
1234 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1239 Sometimes you might want to change the index depending on the type of the
1240 database for which SQL is being generated:
1242 my ($db_type = $sqlt_table->schema->translator->producer_type)
1243 =~ s/^SQL::Translator::Producer:://;
1245 You can also add hooks to the schema level to stop certain tables being
1252 sub sqlt_deploy_hook {
1253 my ($self, $sqlt_schema) = @_;
1255 $sqlt_schema->drop_table('table_name');
1258 You could also add views, procedures or triggers to the output using
1259 L<SQL::Translator::Schema/add_view>,
1260 L<SQL::Translator::Schema/add_procedure> or
1261 L<SQL::Translator::Schema/add_trigger>.
1264 =head2 Schema versioning
1266 The following example shows simplistically how you might use DBIx::Class to
1267 deploy versioned schemas to your customers. The basic process is as follows:
1273 Create a DBIx::Class schema
1285 Modify schema to change functionality
1289 Deploy update to customers
1293 B<Create a DBIx::Class schema>
1295 This can either be done manually, or generated from an existing database as
1296 described under L</Creating Schemas From An Existing Database>
1300 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1302 B<Deploy to customers>
1304 There are several ways you could deploy your schema. These are probably
1305 beyond the scope of this recipe, but might include:
1311 Require customer to apply manually using their RDBMS.
1315 Package along with your app, making database dump/schema update/tests
1316 all part of your install.
1320 B<Modify the schema to change functionality>
1322 As your application evolves, it may be necessary to modify your schema
1323 to change functionality. Once the changes are made to your schema in
1324 DBIx::Class, export the modified schema and the conversion scripts as
1325 in L</Creating DDL SQL>.
1327 B<Deploy update to customers>
1329 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1330 Schema class. This will add a new table to your database called
1331 C<dbix_class_schema_vesion> which will keep track of which version is installed
1332 and warn if the user trys to run a newer schema version than the
1333 database thinks it has.
1335 Alternatively, you can send the conversion sql scripts to your
1338 =head2 Setting quoting for the generated SQL.
1340 If the database contains column names with spaces and/or reserved words, they
1341 need to be quoted in the SQL queries. This is done using:
1343 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1344 __PACKAGE__->storage->sql_maker->name_sep('.');
1346 The first sets the quote characters. Either a pair of matching
1347 brackets, or a C<"> or C<'>:
1349 __PACKAGE__->storage->sql_maker->quote_char('"');
1351 Check the documentation of your database for the correct quote
1352 characters to use. C<name_sep> needs to be set to allow the SQL
1353 generator to put the quotes the correct place.
1355 In most cases you should set these as part of the arguments passed to
1356 L<DBIx::Class::Schema/connect>:
1358 my $schema = My::Schema->connect(
1368 =head2 Setting limit dialect for SQL::Abstract::Limit
1370 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1371 the remote SQL server by looking at the database handle. This is a
1372 common problem when using the DBD::JDBC, since the DBD-driver only
1373 know that in has a Java-driver available, not which JDBC driver the
1374 Java component has loaded. This specifically sets the limit_dialect
1375 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1378 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1380 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1381 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1383 The limit dialect can also be set at connect time by specifying a
1384 C<limit_dialect> key in the final hash as shown above.
1386 =head2 Working with PostgreSQL array types
1388 You can also assign values to PostgreSQL array columns by passing array
1389 references in the C<\%columns> (C<\%vals>) hashref of the
1390 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1393 $resultset->create({
1394 numbers => [1, 2, 3]
1399 numbers => [1, 2, 3]
1406 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1407 methods) you cannot directly use array references (since this is interpreted as
1408 a list of values to be C<OR>ed), but you can use the following syntax to force
1409 passing them as bind values:
1413 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1417 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1418 placeholders and bind values (subqueries)> for more explanation. Note that
1419 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1420 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1421 arrayrefs together with the column name, like this: C<< [column_name => value]
1424 =head1 BOOTSTRAPPING/MIGRATING
1426 =head2 Easy migration from class-based to schema-based setup
1428 You want to start using the schema-based approach to L<DBIx::Class>
1429 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1430 of existing classes that you don't want to move by hand. Try this nifty script
1434 use SQL::Translator;
1436 my $schema = MyDB->schema_instance;
1438 my $translator = SQL::Translator->new(
1439 debug => $debug || 0,
1440 trace => $trace || 0,
1441 no_comments => $no_comments || 0,
1442 show_warnings => $show_warnings || 0,
1443 add_drop_table => $add_drop_table || 0,
1444 validate => $validate || 0,
1446 'DBIx::Schema' => $schema,
1449 'prefix' => 'My::Schema',
1453 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1454 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1456 my $output = $translator->translate(@args) or die
1457 "Error: " . $translator->error;
1461 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1462 namespace, which is currently left as an exercise for the reader.
1464 =head1 OVERLOADING METHODS
1466 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1467 method calls, useful for things like default values and triggers. You have to
1468 use calls to C<next::method> to overload methods. More information on using
1469 L<Class::C3> with L<DBIx::Class> can be found in
1470 L<DBIx::Class::Manual::Component>.
1472 =head2 Setting default values for a row
1474 It's as simple as overriding the C<new> method. Note the use of
1478 my ( $class, $attrs ) = @_;
1480 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1482 my $new = $class->next::method($attrs);
1487 For more information about C<next::method>, look in the L<Class::C3>
1488 documentation. See also L<DBIx::Class::Manual::Component> for more
1489 ways to write your own base classes to do this.
1491 People looking for ways to do "triggers" with DBIx::Class are probably
1492 just looking for this.
1494 =head2 Changing one field whenever another changes
1496 For example, say that you have three columns, C<id>, C<number>, and
1497 C<squared>. You would like to make changes to C<number> and have
1498 C<squared> be automagically set to the value of C<number> squared.
1499 You can accomplish this by overriding C<store_column>:
1502 my ( $self, $name, $value ) = @_;
1503 if ($name eq 'number') {
1504 $self->squared($value * $value);
1506 $self->next::method($name, $value);
1509 Note that the hard work is done by the call to C<next::method>, which
1510 redispatches your call to store_column in the superclass(es).
1512 =head2 Automatically creating related objects
1514 You might have a class C<Artist> which has many C<CD>s. Further, if you
1515 want to create a C<CD> object every time you insert an C<Artist> object.
1516 You can accomplish this by overriding C<insert> on your objects:
1519 my ( $self, @args ) = @_;
1520 $self->next::method(@args);
1521 $self->cds->new({})->fill_from_artist($self)->insert;
1525 where C<fill_from_artist> is a method you specify in C<CD> which sets
1526 values in C<CD> based on the data in the C<Artist> object you pass in.
1528 =head2 Wrapping/overloading a column accessor
1532 Say you have a table "Camera" and want to associate a description
1533 with each camera. For most cameras, you'll be able to generate the description from
1534 the other columns. However, in a few special cases you may want to associate a
1535 custom description with a camera.
1539 In your database schema, define a description field in the "Camera" table that
1540 can contain text and null values.
1542 In DBIC, we'll overload the column accessor to provide a sane default if no
1543 custom description is defined. The accessor will either return or generate the
1544 description, depending on whether the field is null or not.
1546 First, in your "Camera" schema class, define the description field as follows:
1548 __PACKAGE__->add_columns(description => { accessor => '_description' });
1550 Next, we'll define the accessor-wrapper subroutine:
1555 # If there is an update to the column, we'll let the original accessor
1557 return $self->_description(@_) if @_;
1559 # Fetch the column value.
1560 my $description = $self->_description;
1562 # If there's something in the description field, then just return that.
1563 return $description if defined $description && length $descripton;
1565 # Otherwise, generate a description.
1566 return $self->generate_description;
1569 =head1 DEBUGGING AND PROFILING
1571 =head2 DBIx::Class objects with Data::Dumper
1573 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1574 be hard to find the pertinent data in all the data it can generate.
1575 Specifically, if one naively tries to use it like so,
1579 my $cd = $schema->resultset('CD')->find(1);
1582 several pages worth of data from the CD object's schema and result source will
1583 be dumped to the screen. Since usually one is only interested in a few column
1584 values of the object, this is not very helpful.
1586 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1587 it. Simply define a hook that L<Data::Dumper> will call on the object before
1588 dumping it. For example,
1595 result_source => undef,
1603 local $Data::Dumper::Freezer = '_dumper_hook';
1605 my $cd = $schema->resultset('CD')->find(1);
1607 # dumps $cd without its ResultSource
1609 If the structure of your schema is such that there is a common base class for
1610 all your table classes, simply put a method similar to C<_dumper_hook> in the
1611 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1612 will automagically clean up your data before printing it. See
1613 L<Data::Dumper/EXAMPLES> for more information.
1617 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1618 executed as well as notifications of query completion and transaction
1619 begin/commit. If you'd like to profile the SQL you can subclass the
1620 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1623 package My::Profiler;
1626 use base 'DBIx::Class::Storage::Statistics';
1628 use Time::HiRes qw(time);
1637 $self->print("Executing $sql: ".join(', ', @params)."\n");
1646 my $elapsed = sprintf("%0.4f", time() - $start);
1647 $self->print("Execution took $elapsed seconds.\n");
1653 You can then install that class as the debugging object:
1655 __PACKAGE__->storage->debugobj(new My::Profiler());
1656 __PACKAGE__->storage->debug(1);
1658 A more complicated example might involve storing each execution of SQL in an
1666 my $elapsed = time() - $start;
1667 push(@{ $calls{$sql} }, {
1673 You could then create average, high and low execution times for an SQL
1674 statement and dig down to see if certain parameters cause aberrant behavior.
1675 You might want to check out L<DBIx::Class::QueryLog> as well.
1677 =head1 STARTUP SPEED
1679 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1680 as the ORM loads all the relevant classes. This section examines
1681 techniques for reducing the startup delay.
1683 These tips are are listed in order of decreasing effectiveness - so the
1684 first tip, if applicable, should have the greatest effect on your
1687 =head2 Statically Define Your Schema
1690 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1691 classes dynamically based on the database schema then there will be a
1692 significant startup delay.
1694 For production use a statically defined schema (which can be generated
1695 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1696 the database schema once - see
1697 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1698 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1699 details on creating static schemas from a database).
1701 =head2 Move Common Startup into a Base Class
1703 Typically L<DBIx::Class> result classes start off with
1705 use base qw/DBIx::Class/;
1706 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1708 If this preamble is moved into a common base class:-
1712 use base qw/DBIx::Class/;
1713 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1716 and each result class then uses this as a base:-
1718 use base qw/MyDBICbase/;
1720 then the load_components is only performed once, which can result in a
1721 considerable startup speedup for schemas with many classes.
1723 =head2 Explicitly List Schema Result Classes
1725 The schema class will normally contain
1727 __PACKAGE__->load_classes();
1729 to load the result classes. This will use L<Module::Find|Module::Find>
1730 to find and load the appropriate modules. Explicitly defining the
1731 classes you wish to load will remove the overhead of
1732 L<Module::Find|Module::Find> and the related directory operations:-
1734 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1736 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1737 syntax to load the appropriate classes there is not a direct alternative
1738 avoiding L<Module::Find|Module::Find>.