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 Predefined searches
300 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
301 and define often used searches as methods:
303 package My::DBIC::ResultSet::CD;
306 use base 'DBIx::Class::ResultSet';
308 sub search_cds_ordered {
311 return $self->search(
313 { order_by => 'name DESC' },
319 To use your resultset, first tell DBIx::Class to create an instance of it
320 for you, in your My::DBIC::Schema::CD class:
322 # class definition as normal
323 __PACKAGE__->load_components(qw/ Core /);
324 __PACKAGE__->table('cd');
326 # tell DBIC to use the custom ResultSet class
327 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
329 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
331 Then call your new method in your code:
333 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
335 =head2 Using SQL functions on the left hand side of a comparison
337 Using SQL functions on the left hand side of a comparison is generally
338 not a good idea since it requires a scan of the entire table. However,
339 it can be accomplished with C<DBIx::Class> when necessary.
341 If you do not have quoting on, simply include the function in your search
342 specification as you would any column:
344 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
346 With quoting on, or for a more portable solution, use the C<where>
349 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
353 (When the bind args ordering bug is fixed, this technique will be better
354 and can replace the one above.)
356 With quoting on, or for a more portable solution, use the C<where> and
360 where => \'YEAR(date_of_birth) = ?',
366 =head1 JOINS AND PREFETCHING
368 =head2 Using joins and prefetch
370 You can use the C<join> attribute to allow searching on, or sorting your
371 results by, one or more columns in a related table. To return all CDs matching
372 a particular artist name:
374 my $rs = $schema->resultset('CD')->search(
376 'artist.name' => 'Bob Marley'
379 join => 'artist', # join the artist table
384 # SELECT cd.* FROM cd
385 # JOIN artist ON cd.artist = artist.id
386 # WHERE artist.name = 'Bob Marley'
388 If required, you can now sort on any column in the related tables by including
389 it in your C<order_by> attribute:
391 my $rs = $schema->resultset('CD')->search(
393 'artist.name' => 'Bob Marley'
397 order_by => [qw/ artist.name /]
402 # SELECT cd.* FROM cd
403 # JOIN artist ON cd.artist = artist.id
404 # WHERE artist.name = 'Bob Marley'
405 # ORDER BY artist.name
407 Note that the C<join> attribute should only be used when you need to search or
408 sort using columns in a related table. Joining related tables when you only
409 need columns from the main table will make performance worse!
411 Now let's say you want to display a list of CDs, each with the name of the
412 artist. The following will work fine:
414 while (my $cd = $rs->next) {
415 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
418 There is a problem however. We have searched both the C<cd> and C<artist> tables
419 in our main query, but we have only returned data from the C<cd> table. To get
420 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
423 SELECT artist.* FROM artist WHERE artist.id = ?
425 A statement like the one above will run for each and every CD returned by our
426 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
429 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
430 This allows you to fetch results from related tables in advance:
432 my $rs = $schema->resultset('CD')->search(
434 'artist.name' => 'Bob Marley'
438 order_by => [qw/ artist.name /],
439 prefetch => 'artist' # return artist data too!
443 # Equivalent SQL (note SELECT from both "cd" and "artist"):
444 # SELECT cd.*, artist.* FROM cd
445 # JOIN artist ON cd.artist = artist.id
446 # WHERE artist.name = 'Bob Marley'
447 # ORDER BY artist.name
449 The code to print the CD list remains the same:
451 while (my $cd = $rs->next) {
452 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
455 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
456 so no additional SQL statements are executed. You now have a much more
459 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
460 C<has_many> relationships.
462 Also note that C<prefetch> should only be used when you know you will
463 definitely use data from a related table. Pre-fetching related tables when you
464 only need columns from the main table will make performance worse!
466 =head2 Multiple joins
468 In the examples above, the C<join> attribute was a scalar. If you
469 pass an array reference instead, you can join to multiple tables. In
470 this example, we want to limit the search further, using
473 # Relationships defined elsewhere:
474 # CD->belongs_to('artist' => 'Artist');
475 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
476 my $rs = $schema->resultset('CD')->search(
478 'artist.name' => 'Bob Marley'
479 'liner_notes.notes' => { 'like', '%some text%' },
482 join => [qw/ artist liner_notes /],
483 order_by => [qw/ artist.name /],
488 # SELECT cd.*, artist.*, liner_notes.* FROM cd
489 # JOIN artist ON cd.artist = artist.id
490 # JOIN liner_notes ON cd.id = liner_notes.cd
491 # WHERE artist.name = 'Bob Marley'
492 # ORDER BY artist.name
494 =head2 Multi-step joins
496 Sometimes you want to join more than one relationship deep. In this example,
497 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
498 contain a specific string:
500 # Relationships defined elsewhere:
501 # Artist->has_many('cds' => 'CD', 'artist');
502 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
504 my $rs = $schema->resultset('Artist')->search(
506 'liner_notes.notes' => { 'like', '%some text%' },
510 'cds' => 'liner_notes'
516 # SELECT artist.* FROM artist
517 # LEFT JOIN cd ON artist.id = cd.artist
518 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
519 # WHERE liner_notes.notes LIKE '%some text%'
521 Joins can be nested to an arbitrary level. So if we decide later that we
522 want to reduce the number of Artists returned based on who wrote the liner
525 # Relationship defined elsewhere:
526 # LinerNotes->belongs_to('author' => 'Person');
528 my $rs = $schema->resultset('Artist')->search(
530 'liner_notes.notes' => { 'like', '%some text%' },
531 'author.name' => 'A. Writer'
536 'liner_notes' => 'author'
543 # SELECT artist.* FROM artist
544 # LEFT JOIN cd ON artist.id = cd.artist
545 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
546 # LEFT JOIN author ON author.id = liner_notes.author
547 # WHERE liner_notes.notes LIKE '%some text%'
548 # AND author.name = 'A. Writer'
550 =head2 Multi-step and multiple joins
552 With various combinations of array and hash references, you can join
553 tables in any combination you desire. For example, to join Artist to
554 CD and Concert, and join CD to LinerNotes:
556 # Relationships defined elsewhere:
557 # Artist->has_many('concerts' => 'Concert', 'artist');
559 my $rs = $schema->resultset('Artist')->search(
572 # SELECT artist.* FROM artist
573 # LEFT JOIN cd ON artist.id = cd.artist
574 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
575 # LEFT JOIN concert ON artist.id = concert.artist
577 =head2 Multi-step prefetch
579 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
580 deep using the same syntax as a multi-step join:
582 my $rs = $schema->resultset('Tag')->search(
592 # SELECT tag.*, cd.*, artist.* FROM tag
593 # JOIN cd ON tag.cd = cd.id
594 # JOIN artist ON cd.artist = artist.id
596 Now accessing our C<cd> and C<artist> relationships does not need additional
599 my $tag = $rs->first;
600 print $tag->cd->artist->name;
602 =head1 ROW-LEVEL OPERATIONS
604 =head2 Retrieving a row object's Schema
606 It is possible to get a Schema object from a row object like so:
608 my $schema = $cd->result_source->schema;
609 # use the schema as normal:
610 my $artist_rs = $schema->resultset('Artist');
612 This can be useful when you don't want to pass around a Schema object to every
615 =head2 Getting the value of the primary key for the last database insert
617 AKA getting last_insert_id
619 If you are using PK::Auto (which is a core component as of 0.07), this is
622 my $foo = $rs->create(\%blah);
624 my $id = $foo->id; # foo->my_primary_key_field will also work.
626 If you are not using autoincrementing primary keys, this will probably
627 not work, but then you already know the value of the last primary key anyway.
629 =head2 Stringification
631 Employ the standard stringification technique by using the C<overload>
634 To make an object stringify itself as a single column, use something
635 like this (replace C<foo> with the column/method of your choice):
637 use overload '""' => sub { shift->name}, fallback => 1;
639 For more complex stringification, you can use an anonymous subroutine:
641 use overload '""' => sub { $_[0]->name . ", " .
642 $_[0]->address }, fallback => 1;
644 =head3 Stringification Example
646 Suppose we have two tables: C<Product> and C<Category>. The table
649 Product(id, Description, category)
650 Category(id, Description)
652 C<category> is a foreign key into the Category table.
654 If you have a Product object C<$obj> and write something like
658 things will not work as expected.
660 To obtain, for example, the category description, you should add this
661 method to the class defining the Category table:
663 use overload "" => sub {
666 return $self->Description;
669 =head2 Want to know if find_or_create found or created a row?
671 Just use C<find_or_new> instead, then check C<in_storage>:
673 my $obj = $rs->find_or_new({ blah => 'blarg' });
674 unless ($obj->in_storage) {
676 # do whatever else you wanted if it was a new row
679 =head2 Dynamic Sub-classing DBIx::Class proxy classes
681 AKA multi-class object inflation from one table
683 L<DBIx::Class> classes are proxy classes, therefore some different
684 techniques need to be employed for more than basic subclassing. In
685 this example we have a single user table that carries a boolean bit
686 for admin. We would like like to give the admin users
687 objects(L<DBIx::Class::Row>) the same methods as a regular user but
688 also special admin only methods. It doesn't make sense to create two
689 seperate proxy-class files for this. We would be copying all the user
690 methods into the Admin class. There is a cleaner way to accomplish
693 Overriding the C<inflate_result> method within the User proxy-class
694 gives us the effect we want. This method is called by
695 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
696 grab the object being returned, inspect the values we are looking for,
697 bless it if it's an admin object, and then return it. See the example
704 use base qw/DBIx::Class::Schema/;
706 __PACKAGE__->load_classes(qw/User/);
709 B<Proxy-Class definitions>
711 package DB::Schema::User;
715 use base qw/DBIx::Class/;
717 ### Defined what our admin class is for ensure_class_loaded
718 my $admin_class = __PACKAGE__ . '::Admin';
720 __PACKAGE__->load_components(qw/Core/);
722 __PACKAGE__->table('users');
724 __PACKAGE__->add_columns(qw/user_id email password
725 firstname lastname active
728 __PACKAGE__->set_primary_key('user_id');
732 my $ret = $self->next::method(@_);
733 if( $ret->admin ) {### If this is an admin rebless for extra functions
734 $self->ensure_class_loaded( $admin_class );
735 bless $ret, $admin_class;
741 print "I am a regular user.\n";
746 package DB::Schema::User::Admin;
750 use base qw/DB::Schema::User/;
754 print "I am an admin.\n";
760 print "I am doing admin stuff\n";
770 my $user_data = { email => 'someguy@place.com',
774 my $admin_data = { email => 'someadmin@adminplace.com',
778 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
780 $schema->resultset('User')->create( $user_data );
781 $schema->resultset('User')->create( $admin_data );
783 ### Now we search for them
784 my $user = $schema->resultset('User')->single( $user_data );
785 my $admin = $schema->resultset('User')->single( $admin_data );
787 print ref $user, "\n";
788 print ref $admin, "\n";
790 print $user->password , "\n"; # pass1
791 print $admin->password , "\n";# pass2; inherited from User
792 print $user->hello , "\n";# I am a regular user.
793 print $admin->hello, "\n";# I am an admin.
795 ### The statement below will NOT print
796 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
797 ### The statement below will print
798 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
800 =head2 Skip row object creation for faster results
802 DBIx::Class is not built for speed, it's built for convenience and
803 ease of use, but sometimes you just need to get the data, and skip the
806 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
808 my $rs = $schema->resultset('CD');
810 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
812 my $hash_ref = $rs->find(1);
816 =head2 Get raw data for blindingly fast results
818 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
819 above is not fast enough for you, you can use a DBIx::Class to return values
820 exactly as they come out of the data base with none of the convenience methods
823 This is used like so:-
825 my $cursor = $rs->cursor
826 while (my @vals = $cursor->next) {
827 # use $val[0..n] here
830 You will need to map the array offsets to particular columns (you can
831 use the I<select> attribute of C<search()> to force ordering).
833 =head1 RESULTSET OPERATIONS
835 =head2 Getting Schema from a ResultSet
837 To get the schema object from a result set, do the following:
839 $rs->result_source->schema
841 =head2 Getting Columns Of Data
845 If you want to find the sum of a particular column there are several
846 ways, the obvious one is to use search:
848 my $rs = $schema->resultset('Items')->search(
851 select => [ { sum => 'Cost' } ],
852 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
855 my $tc = $rs->first->get_column('total_cost');
857 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
858 returned when you ask the C<ResultSet> for a column using
861 my $cost = $schema->resultset('Items')->get_column('Cost');
864 With this you can also do:
866 my $minvalue = $cost->min;
867 my $maxvalue = $cost->max;
869 Or just iterate through the values of this column only:
871 while ( my $c = $cost->next ) {
875 foreach my $c ($cost->all) {
879 C<ResultSetColumn> only has a limited number of built-in functions, if
880 you need one that it doesn't have, then you can use the C<func> method
883 my $avg = $cost->func('AVERAGE');
885 This will cause the following SQL statement to be run:
887 SELECT AVERAGE(Cost) FROM Items me
889 Which will of course only work if your database supports this function.
890 See L<DBIx::Class::ResultSetColumn> for more documentation.
892 =head2 Creating a result set from a set of rows
894 Sometimes you have a (set of) row objects that you want to put into a
895 resultset without the need to hit the DB again. You can do that by using the
896 L<set_cache|DBIx::Class::Resultset/set_cache> method:
898 my @uploadable_groups;
899 while (my $group = $groups->next) {
900 if ($group->can_upload($self)) {
901 push @uploadable_groups, $group;
904 my $new_rs = $self->result_source->resultset;
905 $new_rs->set_cache(\@uploadable_groups);
909 =head1 USING RELATIONSHIPS
911 =head2 Create a new row in a related table
913 my $author = $book->create_related('author', { name => 'Fred'});
915 =head2 Search in a related table
917 Only searches for books named 'Titanic' by the author in $author.
919 my $books_rs = $author->search_related('books', { name => 'Titanic' });
921 =head2 Delete data in a related table
923 Deletes only the book named Titanic by the author in $author.
925 $author->delete_related('books', { name => 'Titanic' });
927 =head2 Ordering a relationship result set
929 If you always want a relation to be ordered, you can specify this when you
930 create the relationship.
932 To order C<< $book->pages >> by descending page_number, create the relation
935 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
937 =head2 Filtering a relationship result set
939 If you want to get a filtered result set, you can just add add to $attr as follows:
941 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
943 =head2 Many-to-many relationships
945 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
948 use base 'DBIx::Class';
949 __PACKAGE__->load_components('Core');
950 __PACKAGE__->table('user');
951 __PACKAGE__->add_columns(qw/id name/);
952 __PACKAGE__->set_primary_key('id');
953 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
954 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
956 package My::UserAddress;
957 use base 'DBIx::Class';
958 __PACKAGE__->load_components('Core');
959 __PACKAGE__->table('user_address');
960 __PACKAGE__->add_columns(qw/user address/);
961 __PACKAGE__->set_primary_key(qw/user address/);
962 __PACKAGE__->belongs_to('user' => 'My::User');
963 __PACKAGE__->belongs_to('address' => 'My::Address');
966 use base 'DBIx::Class';
967 __PACKAGE__->load_components('Core');
968 __PACKAGE__->table('address');
969 __PACKAGE__->add_columns(qw/id street town area_code country/);
970 __PACKAGE__->set_primary_key('id');
971 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
972 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
974 $rs = $user->addresses(); # get all addresses for a user
975 $rs = $address->users(); # get all users for an address
979 As of version 0.04001, there is improved transaction support in
980 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
981 example of the recommended way to use it:
983 my $genus = $schema->resultset('Genus')->find(12);
991 $genus->add_to_species({ name => 'troglodyte' });
994 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
995 return $genus->species;
1000 $rs = $schema->txn_do($coderef1);
1003 if ($@) { # Transaction failed
1004 die "the sky is falling!" #
1005 if ($@ =~ /Rollback failed/); # Rollback failed
1007 deal_with_failed_transaction();
1010 Nested transactions will work as expected. That is, only the outermost
1011 transaction will actually issue a commit to the $dbh, and a rollback
1012 at any level of any transaction will cause the entire nested
1013 transaction to fail. Support for savepoints and for true nested
1014 transactions (for databases that support them) will hopefully be added
1019 =head2 Creating Schemas From An Existing Database
1021 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1022 L<DBIx::Class::Schema> and associated sources by examining the database.
1024 The recommend way of achieving this is to use the
1025 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1027 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1028 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1030 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1031 source definitions for all the tables found in the C<foo> database.
1033 =head2 Creating DDL SQL
1035 The following functionality requires you to have L<SQL::Translator>
1036 (also known as "SQL Fairy") installed.
1038 To create a set of database-specific .sql files for the above schema:
1040 my $schema = My::Schema->connect($dsn);
1041 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1046 By default this will create schema files in the current directory, for
1047 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1049 To create a new database using the schema:
1051 my $schema = My::Schema->connect($dsn);
1052 $schema->deploy({ add_drop_tables => 1});
1054 To import created .sql files using the mysql client:
1056 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1058 To create C<ALTER TABLE> conversion scripts to update a database to a
1059 newer version of your schema at a later point, first set a new
1060 C<$VERSION> in your Schema file, then:
1062 my $schema = My::Schema->connect($dsn);
1063 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1069 This will produce new database-specific .sql files for the new version
1070 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1071 requires that the files for 0.1 as created above are available in the
1072 given directory to diff against.
1074 =head2 Select from dual
1076 Dummy tables are needed by some databases to allow calling functions
1077 or expressions that aren't based on table content, for examples of how
1078 this applies to various database types, see:
1079 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1081 Note: If you're using Oracles dual table don't B<ever> do anything
1082 other than a select, if you CRUD on your dual table you *will* break
1085 Make a table class as you would for any other table
1087 package MyAppDB::Dual;
1090 use base 'DBIx::Class';
1091 __PACKAGE__->load_components("Core");
1092 __PACKAGE__->table("Dual");
1093 __PACKAGE__->add_columns(
1095 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1098 Once you've loaded your table class select from it using C<select>
1099 and C<as> instead of C<columns>
1101 my $rs = $schema->resultset('Dual')->search(undef,
1102 { select => [ 'sydate' ],
1107 All you have to do now is be careful how you access your resultset, the below
1108 will not work because there is no column called 'now' in the Dual table class
1110 while (my $dual = $rs->next) {
1111 print $dual->now."\n";
1113 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1115 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1116 your Dual class for whatever you wanted to select from dual, but that's just
1117 silly, instead use C<get_column>
1119 while (my $dual = $rs->next) {
1120 print $dual->get_column('now')."\n";
1125 my $cursor = $rs->cursor;
1126 while (my @vals = $cursor->next) {
1127 print $vals[0]."\n";
1130 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1132 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1133 while ( my $dual = $rs->next ) {
1134 print $dual->{now}."\n";
1137 Here are some example C<select> conditions to illustrate the different syntax
1138 you could use for doing stuff like
1139 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1141 # get a sequence value
1142 select => [ 'A_SEQ.nextval' ],
1144 # get create table sql
1145 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1147 # get a random num between 0 and 100
1148 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1151 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1154 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1156 # which day of the week were you born on?
1157 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1159 # select 16 rows from dual
1160 select => [ "'hello'" ],
1162 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1166 =head2 Adding Indexes And Functions To Your SQL
1168 Often you will want indexes on columns on your table to speed up searching. To
1169 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1172 package My::Schema::Artist;
1174 __PACKAGE__->table('artist');
1175 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1177 sub sqlt_deploy_hook {
1178 my ($self, $sqlt_table) = @_;
1180 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1185 Sometimes you might want to change the index depending on the type of the
1186 database for which SQL is being generated:
1188 my ($db_type = $sqlt_table->schema->translator->producer_type)
1189 =~ s/^SQL::Translator::Producer:://;
1191 You can also add hooks to the schema level to stop certain tables being
1198 sub sqlt_deploy_hook {
1199 my ($self, $sqlt_schema) = @_;
1201 $sqlt_schema->drop_table('table_name');
1204 You could also add views or procedures to the output using
1205 L<SQL::Translator::Schema/add_view> or
1206 L<SQL::Translator::Schema/add_procedure>.
1208 =head2 Schema versioning
1210 The following example shows simplistically how you might use DBIx::Class to
1211 deploy versioned schemas to your customers. The basic process is as follows:
1217 Create a DBIx::Class schema
1229 Modify schema to change functionality
1233 Deploy update to customers
1237 B<Create a DBIx::Class schema>
1239 This can either be done manually, or generated from an existing database as
1240 described under L</Creating Schemas From An Existing Database>
1244 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1246 B<Deploy to customers>
1248 There are several ways you could deploy your schema. These are probably
1249 beyond the scope of this recipe, but might include:
1255 Require customer to apply manually using their RDBMS.
1259 Package along with your app, making database dump/schema update/tests
1260 all part of your install.
1264 B<Modify the schema to change functionality>
1266 As your application evolves, it may be necessary to modify your schema
1267 to change functionality. Once the changes are made to your schema in
1268 DBIx::Class, export the modified schema and the conversion scripts as
1269 in L</Creating DDL SQL>.
1271 B<Deploy update to customers>
1273 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1274 Schema class. This will add a new table to your database called
1275 C<dbix_class_schema_vesion> which will keep track of which version is installed
1276 and warn if the user trys to run a newer schema version than the
1277 database thinks it has.
1279 Alternatively, you can send the conversion sql scripts to your
1282 =head2 Setting quoting for the generated SQL.
1284 If the database contains column names with spaces and/or reserved words, they
1285 need to be quoted in the SQL queries. This is done using:
1287 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1288 __PACKAGE__->storage->sql_maker->name_sep('.');
1290 The first sets the quote characters. Either a pair of matching
1291 brackets, or a C<"> or C<'>:
1293 __PACKAGE__->storage->sql_maker->quote_char('"');
1295 Check the documentation of your database for the correct quote
1296 characters to use. C<name_sep> needs to be set to allow the SQL
1297 generator to put the quotes the correct place.
1299 In most cases you should set these as part of the arguments passed to
1300 L<DBIx::Class::Schema/connect>:
1302 my $schema = My::Schema->connect(
1312 =head2 Setting limit dialect for SQL::Abstract::Limit
1314 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1315 the remote SQL server by looking at the database handle. This is a
1316 common problem when using the DBD::JDBC, since the DBD-driver only
1317 know that in has a Java-driver available, not which JDBC driver the
1318 Java component has loaded. This specifically sets the limit_dialect
1319 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1322 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1324 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1325 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1327 The limit dialect can also be set at connect time by specifying a
1328 C<limit_dialect> key in the final hash as shown above.
1330 =head2 Working with PostgreSQL array types
1332 If your SQL::Abstract version (>= 1.50) supports it, you can assign to
1333 PostgreSQL array values by passing array references in the C<\%columns>
1334 (C<\%vals>) hashref of the L<DBIx::Class::ResultSet/create> and
1335 L<DBIx::Class::Row/update> family of methods:
1337 $resultset->create({
1338 numbers => [1, 2, 3]
1343 numbers => [1, 2, 3]
1350 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1351 methods) you cannot directly use array references (since this is interpreted as
1352 a list of values to be C<OR>ed), but you can use the following syntax to force
1353 passing them as bind values:
1357 numbers => \[ '= ?', [1, 2, 3] ]
1361 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1362 placeholders and bind values (subqueries)> for more explanation.
1364 =head1 BOOTSTRAPPING/MIGRATING
1366 =head2 Easy migration from class-based to schema-based setup
1368 You want to start using the schema-based approach to L<DBIx::Class>
1369 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1370 of existing classes that you don't want to move by hand. Try this nifty script
1374 use SQL::Translator;
1376 my $schema = MyDB->schema_instance;
1378 my $translator = SQL::Translator->new(
1379 debug => $debug || 0,
1380 trace => $trace || 0,
1381 no_comments => $no_comments || 0,
1382 show_warnings => $show_warnings || 0,
1383 add_drop_table => $add_drop_table || 0,
1384 validate => $validate || 0,
1386 'DBIx::Schema' => $schema,
1389 'prefix' => 'My::Schema',
1393 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1394 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1396 my $output = $translator->translate(@args) or die
1397 "Error: " . $translator->error;
1401 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1402 namespace, which is currently left as an exercise for the reader.
1404 =head1 OVERLOADING METHODS
1406 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1407 method calls, useful for things like default values and triggers. You have to
1408 use calls to C<next::method> to overload methods. More information on using
1409 L<Class::C3> with L<DBIx::Class> can be found in
1410 L<DBIx::Class::Manual::Component>.
1412 =head2 Setting default values for a row
1414 It's as simple as overriding the C<new> method. Note the use of
1418 my ( $class, $attrs ) = @_;
1420 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1422 my $new = $class->next::method($attrs);
1427 For more information about C<next::method>, look in the L<Class::C3>
1428 documentation. See also L<DBIx::Class::Manual::Component> for more
1429 ways to write your own base classes to do this.
1431 People looking for ways to do "triggers" with DBIx::Class are probably
1432 just looking for this.
1434 =head2 Changing one field whenever another changes
1436 For example, say that you have three columns, C<id>, C<number>, and
1437 C<squared>. You would like to make changes to C<number> and have
1438 C<squared> be automagically set to the value of C<number> squared.
1439 You can accomplish this by overriding C<store_column>:
1442 my ( $self, $name, $value ) = @_;
1443 if ($name eq 'number') {
1444 $self->squared($value * $value);
1446 $self->next::method($name, $value);
1449 Note that the hard work is done by the call to C<next::method>, which
1450 redispatches your call to store_column in the superclass(es).
1452 =head2 Automatically creating related objects
1454 You might have a class C<Artist> which has many C<CD>s. Further, if you
1455 want to create a C<CD> object every time you insert an C<Artist> object.
1456 You can accomplish this by overriding C<insert> on your objects:
1459 my ( $self, @args ) = @_;
1460 $self->next::method(@args);
1461 $self->cds->new({})->fill_from_artist($self)->insert;
1465 where C<fill_from_artist> is a method you specify in C<CD> which sets
1466 values in C<CD> based on the data in the C<Artist> object you pass in.
1468 =head2 Wrapping/overloading a column accessor
1472 Say you have a table "Camera" and want to associate a description
1473 with each camera. For most cameras, you'll be able to generate the description from
1474 the other columns. However, in a few special cases you may want to associate a
1475 custom description with a camera.
1479 In your database schema, define a description field in the "Camera" table that
1480 can contain text and null values.
1482 In DBIC, we'll overload the column accessor to provide a sane default if no
1483 custom description is defined. The accessor will either return or generate the
1484 description, depending on whether the field is null or not.
1486 First, in your "Camera" schema class, define the description field as follows:
1488 __PACKAGE__->add_columns(description => { accessor => '_description' });
1490 Next, we'll define the accessor-wrapper subroutine:
1495 # If there is an update to the column, we'll let the original accessor
1497 return $self->_description(@_) if @_;
1499 # Fetch the column value.
1500 my $description = $self->_description;
1502 # If there's something in the description field, then just return that.
1503 return $description if defined $description && length $descripton;
1505 # Otherwise, generate a description.
1506 return $self->generate_description;
1509 =head1 DEBUGGING AND PROFILING
1511 =head2 DBIx::Class objects with Data::Dumper
1513 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1514 be hard to find the pertinent data in all the data it can generate.
1515 Specifically, if one naively tries to use it like so,
1519 my $cd = $schema->resultset('CD')->find(1);
1522 several pages worth of data from the CD object's schema and result source will
1523 be dumped to the screen. Since usually one is only interested in a few column
1524 values of the object, this is not very helpful.
1526 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1527 it. Simply define a hook that L<Data::Dumper> will call on the object before
1528 dumping it. For example,
1535 result_source => undef,
1543 local $Data::Dumper::Freezer = '_dumper_hook';
1545 my $cd = $schema->resultset('CD')->find(1);
1547 # dumps $cd without its ResultSource
1549 If the structure of your schema is such that there is a common base class for
1550 all your table classes, simply put a method similar to C<_dumper_hook> in the
1551 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1552 will automagically clean up your data before printing it. See
1553 L<Data::Dumper/EXAMPLES> for more information.
1557 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1558 executed as well as notifications of query completion and transaction
1559 begin/commit. If you'd like to profile the SQL you can subclass the
1560 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1563 package My::Profiler;
1566 use base 'DBIx::Class::Storage::Statistics';
1568 use Time::HiRes qw(time);
1577 $self->print("Executing $sql: ".join(', ', @params)."\n");
1586 my $elapsed = sprintf("%0.4f", time() - $start);
1587 $self->print("Execution took $elapsed seconds.\n");
1593 You can then install that class as the debugging object:
1595 __PACKAGE__->storage->debugobj(new My::Profiler());
1596 __PACKAGE__->storage->debug(1);
1598 A more complicated example might involve storing each execution of SQL in an
1606 my $elapsed = time() - $start;
1607 push(@{ $calls{$sql} }, {
1613 You could then create average, high and low execution times for an SQL
1614 statement and dig down to see if certain parameters cause aberrant behavior.
1615 You might want to check out L<DBIx::Class::QueryLog> as well.