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 Arbitrary SQL through a custom ResultSource
73 Sometimes you have to run arbitrary SQL because your query is too complex
74 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
75 be optimized for your database in a special way, but you still want to
76 get the results as a L<DBIx::Class::ResultSet>.
77 The recommended way to accomplish this is by defining a separate ResultSource
78 for your query. You can then inject complete SQL statements using a scalar
79 reference (this is a feature of L<SQL::Abstract>).
81 Say you want to run a complex custom query on your user data, here's what
82 you have to add to your User class:
84 package My::Schema::User;
86 use base qw/DBIx::Class/;
88 # ->load_components, ->table, ->add_columns, etc.
90 # Make a new ResultSource based on the User class
91 my $source = __PACKAGE__->result_source_instance();
92 my $new_source = $source->new( $source );
93 $new_source->source_name( 'UserFriendsComplex' );
95 # Hand in your query as a scalar reference
96 # It will be added as a sub-select after FROM,
97 # so pay attention to the surrounding brackets!
98 $new_source->name( \<<SQL );
99 ( SELECT u.* FROM user u
100 INNER JOIN user_friends f ON u.id = f.user_id
101 WHERE f.friend_user_id = ?
103 SELECT u.* FROM user u
104 INNER JOIN user_friends f ON u.id = f.friend_user_id
105 WHERE f.user_id = ? )
108 # Finally, register your new ResultSource with your Schema
109 My::Schema->register_source( 'UserFriendsComplex' => $new_source );
111 Next, you can execute your complex query using bind parameters like this:
113 my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {},
115 bind => [ 12345, 12345 ]
119 ... and you'll get back a perfect L<DBIx::Class::ResultSet>.
121 =head2 Using specific columns
123 When you only want specific columns from a table, you can use
124 C<columns> to specify which ones you need. This is useful to avoid
125 loading columns with large amounts of data that you aren't about to
128 my $rs = $schema->resultset('Artist')->search(
131 columns => [qw/ name /]
136 # SELECT artist.name FROM artist
138 This is a shortcut for C<select> and C<as>, see below. C<columns>
139 cannot be used together with C<select> and C<as>.
141 =head2 Using database functions or stored procedures
143 The combination of C<select> and C<as> can be used to return the result of a
144 database function or stored procedure as a column value. You use C<select> to
145 specify the source for your column value (e.g. a column name, function, or
146 stored procedure name). You then use C<as> to set the column name you will use
147 to access the returned value:
149 my $rs = $schema->resultset('Artist')->search(
152 select => [ 'name', { LENGTH => 'name' } ],
153 as => [qw/ name name_length /],
158 # SELECT name name, LENGTH( name )
161 Note that the C< as > attribute has absolutely nothing to with the sql
162 syntax C< SELECT foo AS bar > (see the documentation in
163 L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
164 column in your base class (i.e. it was added with C<add_columns>), you
165 just access it as normal. Our C<Artist> class has a C<name> column, so
166 we just use the C<name> accessor:
168 my $artist = $rs->first();
169 my $name = $artist->name();
171 If on the other hand the alias does not correspond to an existing column, you
172 have to fetch the value using the C<get_column> accessor:
174 my $name_length = $artist->get_column('name_length');
176 If you don't like using C<get_column>, you can always create an accessor for
177 any of your aliases using either of these:
179 # Define accessor manually:
180 sub name_length { shift->get_column('name_length'); }
182 # Or use DBIx::Class::AccessorGroup:
183 __PACKAGE__->mk_group_accessors('column' => 'name_length');
185 =head2 SELECT DISTINCT with multiple columns
187 my $rs = $schema->resultset('Foo')->search(
191 { distinct => [ $source->columns ] }
193 as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
197 =head2 SELECT COUNT(DISTINCT colname)
199 my $rs = $schema->resultset('Foo')->search(
203 { count => { distinct => 'colname' } }
209 my $count = $rs->next->get_column('count');
211 =head2 Grouping results
213 L<DBIx::Class> supports C<GROUP BY> as follows:
215 my $rs = $schema->resultset('Artist')->search(
219 select => [ 'name', { count => 'cds.id' } ],
220 as => [qw/ name cd_count /],
221 group_by => [qw/ name /]
226 # SELECT name, COUNT( cd.id ) FROM artist
227 # LEFT JOIN cd ON artist.id = cd.artist
230 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
231 are in any way unsure about the use of the attributes above (C< join
232 >, C< select >, C< as > and C< group_by >).
234 =head2 Predefined searches
236 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
237 and define often used searches as methods:
239 package My::DBIC::ResultSet::CD;
242 use base 'DBIx::Class::ResultSet';
244 sub search_cds_ordered {
247 return $self->search(
249 { order_by => 'name DESC' },
255 To use your resultset, first tell DBIx::Class to create an instance of it
256 for you, in your My::DBIC::Schema::CD class:
258 # class definition as normal
259 __PACKAGE__->load_components(qw/ Core /);
260 __PACKAGE__->table('cd');
262 # tell DBIC to use the custom ResultSet class
263 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
265 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
267 Then call your new method in your code:
269 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
271 =head2 Using SQL functions on the left hand side of a comparison
273 Using SQL functions on the left hand side of a comparison is generally
274 not a good idea since it requires a scan of the entire table. However,
275 it can be accomplished with C<DBIx::Class> when necessary.
277 If you do not have quoting on, simply include the function in your search
278 specification as you would any column:
280 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
282 With quoting on, or for a more portable solution, use the C<where>
285 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
289 (When the bind args ordering bug is fixed, this technique will be better
290 and can replace the one above.)
292 With quoting on, or for a more portable solution, use the C<where> and
296 where => \'YEAR(date_of_birth) = ?',
302 =head1 JOINS AND PREFETCHING
304 =head2 Using joins and prefetch
306 You can use the C<join> attribute to allow searching on, or sorting your
307 results by, one or more columns in a related table. To return all CDs matching
308 a particular artist name:
310 my $rs = $schema->resultset('CD')->search(
312 'artist.name' => 'Bob Marley'
315 join => 'artist', # join the artist table
320 # SELECT cd.* FROM cd
321 # JOIN artist ON cd.artist = artist.id
322 # WHERE artist.name = 'Bob Marley'
324 If required, you can now sort on any column in the related tables by including
325 it in your C<order_by> attribute:
327 my $rs = $schema->resultset('CD')->search(
329 'artist.name' => 'Bob Marley'
333 order_by => [qw/ artist.name /]
338 # SELECT cd.* FROM cd
339 # JOIN artist ON cd.artist = artist.id
340 # WHERE artist.name = 'Bob Marley'
341 # ORDER BY artist.name
343 Note that the C<join> attribute should only be used when you need to search or
344 sort using columns in a related table. Joining related tables when you only
345 need columns from the main table will make performance worse!
347 Now let's say you want to display a list of CDs, each with the name of the
348 artist. The following will work fine:
350 while (my $cd = $rs->next) {
351 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
354 There is a problem however. We have searched both the C<cd> and C<artist> tables
355 in our main query, but we have only returned data from the C<cd> table. To get
356 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
359 SELECT artist.* FROM artist WHERE artist.id = ?
361 A statement like the one above will run for each and every CD returned by our
362 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
365 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
366 This allows you to fetch results from related tables in advance:
368 my $rs = $schema->resultset('CD')->search(
370 'artist.name' => 'Bob Marley'
374 order_by => [qw/ artist.name /],
375 prefetch => 'artist' # return artist data too!
379 # Equivalent SQL (note SELECT from both "cd" and "artist"):
380 # SELECT cd.*, artist.* FROM cd
381 # JOIN artist ON cd.artist = artist.id
382 # WHERE artist.name = 'Bob Marley'
383 # ORDER BY artist.name
385 The code to print the CD list remains the same:
387 while (my $cd = $rs->next) {
388 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
391 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
392 so no additional SQL statements are executed. You now have a much more
395 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
396 C<has_many> relationships.
398 Also note that C<prefetch> should only be used when you know you will
399 definitely use data from a related table. Pre-fetching related tables when you
400 only need columns from the main table will make performance worse!
402 =head2 Multiple joins
404 In the examples above, the C<join> attribute was a scalar. If you
405 pass an array reference instead, you can join to multiple tables. In
406 this example, we want to limit the search further, using
409 # Relationships defined elsewhere:
410 # CD->belongs_to('artist' => 'Artist');
411 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
412 my $rs = $schema->resultset('CD')->search(
414 'artist.name' => 'Bob Marley'
415 'liner_notes.notes' => { 'like', '%some text%' },
418 join => [qw/ artist liner_notes /],
419 order_by => [qw/ artist.name /],
424 # SELECT cd.*, artist.*, liner_notes.* FROM cd
425 # JOIN artist ON cd.artist = artist.id
426 # JOIN liner_notes ON cd.id = liner_notes.cd
427 # WHERE artist.name = 'Bob Marley'
428 # ORDER BY artist.name
430 =head2 Multi-step joins
432 Sometimes you want to join more than one relationship deep. In this example,
433 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
434 contain a specific string:
436 # Relationships defined elsewhere:
437 # Artist->has_many('cds' => 'CD', 'artist');
438 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
440 my $rs = $schema->resultset('Artist')->search(
442 'liner_notes.notes' => { 'like', '%some text%' },
446 'cds' => 'liner_notes'
452 # SELECT artist.* FROM artist
453 # LEFT JOIN cd ON artist.id = cd.artist
454 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
455 # WHERE liner_notes.notes LIKE '%some text%'
457 Joins can be nested to an arbitrary level. So if we decide later that we
458 want to reduce the number of Artists returned based on who wrote the liner
461 # Relationship defined elsewhere:
462 # LinerNotes->belongs_to('author' => 'Person');
464 my $rs = $schema->resultset('Artist')->search(
466 'liner_notes.notes' => { 'like', '%some text%' },
467 'author.name' => 'A. Writer'
472 'liner_notes' => 'author'
479 # SELECT artist.* FROM artist
480 # LEFT JOIN cd ON artist.id = cd.artist
481 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
482 # LEFT JOIN author ON author.id = liner_notes.author
483 # WHERE liner_notes.notes LIKE '%some text%'
484 # AND author.name = 'A. Writer'
486 =head2 Multi-step and multiple joins
488 With various combinations of array and hash references, you can join
489 tables in any combination you desire. For example, to join Artist to
490 CD and Concert, and join CD to LinerNotes:
492 # Relationships defined elsewhere:
493 # Artist->has_many('concerts' => 'Concert', 'artist');
495 my $rs = $schema->resultset('Artist')->search(
508 # SELECT artist.* FROM artist
509 # LEFT JOIN cd ON artist.id = cd.artist
510 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
511 # LEFT JOIN concert ON artist.id = concert.artist
513 =head2 Multi-step prefetch
515 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
516 deep using the same syntax as a multi-step join:
518 my $rs = $schema->resultset('Tag')->search(
528 # SELECT tag.*, cd.*, artist.* FROM tag
529 # JOIN cd ON tag.cd = cd.id
530 # JOIN artist ON cd.artist = artist.id
532 Now accessing our C<cd> and C<artist> relationships does not need additional
535 my $tag = $rs->first;
536 print $tag->cd->artist->name;
538 =head1 ROW-LEVEL OPERATIONS
540 =head2 Retrieving a row object's Schema
542 It is possible to get a Schema object from a row object like so:
544 my $schema = $cd->result_source->schema;
545 # use the schema as normal:
546 my $artist_rs = $schema->resultset('Artist');
548 This can be useful when you don't want to pass around a Schema object to every
551 =head2 Getting the value of the primary key for the last database insert
553 AKA getting last_insert_id
555 If you are using PK::Auto (which is a core component as of 0.07), this is
558 my $foo = $rs->create(\%blah);
560 my $id = $foo->id; # foo->my_primary_key_field will also work.
562 If you are not using autoincrementing primary keys, this will probably
563 not work, but then you already know the value of the last primary key anyway.
565 =head2 Stringification
567 Employ the standard stringification technique by using the C<overload>
570 To make an object stringify itself as a single column, use something
571 like this (replace C<foo> with the column/method of your choice):
573 use overload '""' => sub { shift->name}, fallback => 1;
575 For more complex stringification, you can use an anonymous subroutine:
577 use overload '""' => sub { $_[0]->name . ", " .
578 $_[0]->address }, fallback => 1;
580 =head3 Stringification Example
582 Suppose we have two tables: C<Product> and C<Category>. The table
585 Product(id, Description, category)
586 Category(id, Description)
588 C<category> is a foreign key into the Category table.
590 If you have a Product object C<$obj> and write something like
594 things will not work as expected.
596 To obtain, for example, the category description, you should add this
597 method to the class defining the Category table:
599 use overload "" => sub {
602 return $self->Description;
605 =head2 Want to know if find_or_create found or created a row?
607 Just use C<find_or_new> instead, then check C<in_storage>:
609 my $obj = $rs->find_or_new({ blah => 'blarg' });
610 unless ($obj->in_storage) {
612 # do whatever else you wanted if it was a new row
615 =head2 Dynamic Sub-classing DBIx::Class proxy classes
617 AKA multi-class object inflation from one table
619 L<DBIx::Class> classes are proxy classes, therefore some different
620 techniques need to be employed for more than basic subclassing. In
621 this example we have a single user table that carries a boolean bit
622 for admin. We would like like to give the admin users
623 objects(L<DBIx::Class::Row>) the same methods as a regular user but
624 also special admin only methods. It doesn't make sense to create two
625 seperate proxy-class files for this. We would be copying all the user
626 methods into the Admin class. There is a cleaner way to accomplish
629 Overriding the C<inflate_result> method within the User proxy-class
630 gives us the effect we want. This method is called by
631 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
632 grab the object being returned, inspect the values we are looking for,
633 bless it if it's an admin object, and then return it. See the example
640 use base qw/DBIx::Class::Schema/;
642 __PACKAGE__->load_classes(qw/User/);
645 B<Proxy-Class definitions>
647 package DB::Schema::User;
651 use base qw/DBIx::Class/;
653 ### Defined what our admin class is for ensure_class_loaded
654 my $admin_class = __PACKAGE__ . '::Admin';
656 __PACKAGE__->load_components(qw/Core/);
658 __PACKAGE__->table('users');
660 __PACKAGE__->add_columns(qw/user_id email password
661 firstname lastname active
664 __PACKAGE__->set_primary_key('user_id');
668 my $ret = $self->next::method(@_);
669 if( $ret->admin ) {### If this is an admin rebless for extra functions
670 $self->ensure_class_loaded( $admin_class );
671 bless $ret, $admin_class;
677 print "I am a regular user.\n";
682 package DB::Schema::User::Admin;
686 use base qw/DB::Schema::User/;
690 print "I am an admin.\n";
696 print "I am doing admin stuff\n";
706 my $user_data = { email => 'someguy@place.com',
710 my $admin_data = { email => 'someadmin@adminplace.com',
714 my $schema = DB::Schema->connection('dbi:Pg:dbname=test');
716 $schema->resultset('User')->create( $user_data );
717 $schema->resultset('User')->create( $admin_data );
719 ### Now we search for them
720 my $user = $schema->resultset('User')->single( $user_data );
721 my $admin = $schema->resultset('User')->single( $admin_data );
723 print ref $user, "\n";
724 print ref $admin, "\n";
726 print $user->password , "\n"; # pass1
727 print $admin->password , "\n";# pass2; inherited from User
728 print $user->hello , "\n";# I am a regular user.
729 print $admin->hello, "\n";# I am an admin.
731 ### The statement below will NOT print
732 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
733 ### The statement below will print
734 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
736 =head2 Skip row object creation for faster results
738 DBIx::Class is not built for speed, it's built for convenience and
739 ease of use, but sometimes you just need to get the data, and skip the
742 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
744 my $rs = $schema->resultset('CD');
746 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
748 my $hash_ref = $rs->find(1);
752 =head2 Skip row object creation for faster results, but still inflate
753 column values to the corresponding objects
755 my $rs = $schema->resultset('CD');
757 $rs->result_class(DBIx::Class::ResultClass::HashRefInflator->new (
761 my $hash_ref = $rs->find(1);
763 =head2 Get raw data for blindingly fast results
765 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
766 above is not fast enough for you, you can use a DBIx::Class to return values
767 exactly as they come out of the data base with none of the convenience methods
770 This is used like so:-
772 my $cursor = $rs->cursor
773 while (my @vals = $cursor->next) {
774 # use $val[0..n] here
777 You will need to map the array offsets to particular columns (you can
778 use the I<select> attribute of C<search()> to force ordering).
780 =head1 RESULTSET OPERATIONS
782 =head2 Getting Schema from a ResultSet
784 To get the schema object from a result set, do the following:
786 $rs->result_source->schema
788 =head2 Getting Columns Of Data
792 If you want to find the sum of a particular column there are several
793 ways, the obvious one is to use search:
795 my $rs = $schema->resultset('Items')->search(
798 select => [ { sum => 'Cost' } ],
799 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
802 my $tc = $rs->first->get_column('total_cost');
804 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
805 returned when you ask the C<ResultSet> for a column using
808 my $cost = $schema->resultset('Items')->get_column('Cost');
811 With this you can also do:
813 my $minvalue = $cost->min;
814 my $maxvalue = $cost->max;
816 Or just iterate through the values of this column only:
818 while ( my $c = $cost->next ) {
822 foreach my $c ($cost->all) {
826 C<ResultSetColumn> only has a limited number of built-in functions, if
827 you need one that it doesn't have, then you can use the C<func> method
830 my $avg = $cost->func('AVERAGE');
832 This will cause the following SQL statement to be run:
834 SELECT AVERAGE(Cost) FROM Items me
836 Which will of course only work if your database supports this function.
837 See L<DBIx::Class::ResultSetColumn> for more documentation.
839 =head2 Creating a result set from a set of rows
841 Sometimes you have a (set of) row objects that you want to put into a
842 resultset without the need to hit the DB again. You can do that by using the
843 L<set_cache|DBIx::Class::Resultset/set_cache> method:
845 my @uploadable_groups;
846 while (my $group = $groups->next) {
847 if ($group->can_upload($self)) {
848 push @uploadable_groups, $group;
851 my $new_rs = $self->result_source->resultset;
852 $new_rs->set_cache(\@uploadable_groups);
856 =head1 USING RELATIONSHIPS
858 =head2 Create a new row in a related table
860 my $author = $book->create_related('author', { name => 'Fred'});
862 =head2 Search in a related table
864 Only searches for books named 'Titanic' by the author in $author.
866 my $books_rs = $author->search_related('books', { name => 'Titanic' });
868 =head2 Delete data in a related table
870 Deletes only the book named Titanic by the author in $author.
872 $author->delete_related('books', { name => 'Titanic' });
874 =head2 Ordering a relationship result set
876 If you always want a relation to be ordered, you can specify this when you
877 create the relationship.
879 To order C<< $book->pages >> by descending page_number, create the relation
882 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
884 =head2 Many-to-many relationships
886 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
889 use base 'DBIx::Class';
890 __PACKAGE__->load_components('Core');
891 __PACKAGE__->table('user');
892 __PACKAGE__->add_columns(qw/id name/);
893 __PACKAGE__->set_primary_key('id');
894 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
895 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
897 package My::UserAddress;
898 use base 'DBIx::Class';
899 __PACKAGE__->load_components('Core');
900 __PACKAGE__->table('user_address');
901 __PACKAGE__->add_columns(qw/user address/);
902 __PACKAGE__->set_primary_key(qw/user address/);
903 __PACKAGE__->belongs_to('user' => 'My::User');
904 __PACKAGE__->belongs_to('address' => 'My::Address');
907 use base 'DBIx::Class';
908 __PACKAGE__->load_components('Core');
909 __PACKAGE__->table('address');
910 __PACKAGE__->add_columns(qw/id street town area_code country/);
911 __PACKAGE__->set_primary_key('id');
912 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
913 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
915 $rs = $user->addresses(); # get all addresses for a user
916 $rs = $address->users(); # get all users for an address
920 As of version 0.04001, there is improved transaction support in
921 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
922 example of the recommended way to use it:
924 my $genus = $schema->resultset('Genus')->find(12);
932 $genus->add_to_species({ name => 'troglodyte' });
935 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
936 return $genus->species;
941 $rs = $schema->txn_do($coderef1);
944 if ($@) { # Transaction failed
945 die "the sky is falling!" #
946 if ($@ =~ /Rollback failed/); # Rollback failed
948 deal_with_failed_transaction();
951 Nested transactions will work as expected. That is, only the outermost
952 transaction will actually issue a commit to the $dbh, and a rollback
953 at any level of any transaction will cause the entire nested
954 transaction to fail. Support for savepoints and for true nested
955 transactions (for databases that support them) will hopefully be added
960 =head2 Creating Schemas From An Existing Database
962 L<DBIx::Class::Schema::Loader> will connect to a database and create a
963 L<DBIx::Class::Schema> and associated sources by examining the database.
965 The recommend way of achieving this is to use the
966 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
968 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
969 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
971 This will create a tree of files rooted at C<./lib/My/Schema/> containing
972 source definitions for all the tables found in the C<foo> database.
974 =head2 Creating DDL SQL
976 The following functionality requires you to have L<SQL::Translator>
977 (also known as "SQL Fairy") installed.
979 To create a set of database-specific .sql files for the above schema:
981 my $schema = My::Schema->connect($dsn);
982 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
987 By default this will create schema files in the current directory, for
988 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
990 To create a new database using the schema:
992 my $schema = My::Schema->connect($dsn);
993 $schema->deploy({ add_drop_tables => 1});
995 To import created .sql files using the mysql client:
997 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
999 To create C<ALTER TABLE> conversion scripts to update a database to a
1000 newer version of your schema at a later point, first set a new
1001 C<$VERSION> in your Schema file, then:
1003 my $schema = My::Schema->connect($dsn);
1004 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1010 This will produce new database-specific .sql files for the new version
1011 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1012 requires that the files for 0.1 as created above are available in the
1013 given directory to diff against.
1015 =head2 Select from dual
1017 Dummy tables are needed by some databases to allow calling functions
1018 or expressions that aren't based on table content, for examples of how
1019 this applies to various database types, see:
1020 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1022 Note: If you're using Oracles dual table don't B<ever> do anything
1023 other than a select, if you CRUD on your dual table you *will* break
1026 Make a table class as you would for any other table
1028 package MyAppDB::Dual;
1031 use base 'DBIx::Class';
1032 __PACKAGE__->load_components("Core");
1033 __PACKAGE__->table("Dual");
1034 __PACKAGE__->add_columns(
1036 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1039 Once you've loaded your table class select from it using C<select>
1040 and C<as> instead of C<columns>
1042 my $rs = $schema->resultset('Dual')->search(undef,
1043 { select => [ 'sydate' ],
1048 All you have to do now is be careful how you access your resultset, the below
1049 will not work because there is no column called 'now' in the Dual table class
1051 while (my $dual = $rs->next) {
1052 print $dual->now."\n";
1054 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1056 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1057 your Dual class for whatever you wanted to select from dual, but that's just
1058 silly, instead use C<get_column>
1060 while (my $dual = $rs->next) {
1061 print $dual->get_column('now')."\n";
1066 my $cursor = $rs->cursor;
1067 while (my @vals = $cursor->next) {
1068 print $vals[0]."\n";
1071 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1073 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1074 while ( my $dual = $rs->next ) {
1075 print $dual->{now}."\n";
1078 Here are some example C<select> conditions to illustrate the different syntax
1079 you could use for doing stuff like
1080 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1082 # get a sequence value
1083 select => [ 'A_SEQ.nextval' ],
1085 # get create table sql
1086 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1088 # get a random num between 0 and 100
1089 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1092 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1095 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1097 # which day of the week were you born on?
1098 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1100 # select 16 rows from dual
1101 select => [ "'hello'" ],
1103 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1107 =head2 Adding Indexes And Functions To Your SQL
1109 Often you will want indexes on columns on your table to speed up searching. To
1110 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1113 package My::Schema::Artist;
1115 __PACKAGE__->table('artist');
1116 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1118 sub sqlt_deploy_hook {
1119 my ($self, $sqlt_table) = @_;
1121 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1126 Sometimes you might want to change the index depending on the type of the
1127 database for which SQL is being generated:
1129 my ($db_type = $sqlt_table->schema->translator->producer_type)
1130 =~ s/^SQL::Translator::Producer:://;
1132 You can also add hooks to the schema level to stop certain tables being
1139 sub sqlt_deploy_hook {
1140 my ($self, $sqlt_schema) = @_;
1142 $sqlt_schema->drop_table('table_name');
1145 You could also add views or procedures to the output using
1146 L<SQL::Translator::Schema/add_view> or
1147 L<SQL::Translator::Schema/add_procedure>.
1149 =head2 Schema versioning
1151 The following example shows simplistically how you might use DBIx::Class to
1152 deploy versioned schemas to your customers. The basic process is as follows:
1158 Create a DBIx::Class schema
1170 Modify schema to change functionality
1174 Deploy update to customers
1178 B<Create a DBIx::Class schema>
1180 This can either be done manually, or generated from an existing database as
1181 described under L</Creating Schemas From An Existing Database>
1185 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1187 B<Deploy to customers>
1189 There are several ways you could deploy your schema. These are probably
1190 beyond the scope of this recipe, but might include:
1196 Require customer to apply manually using their RDBMS.
1200 Package along with your app, making database dump/schema update/tests
1201 all part of your install.
1205 B<Modify the schema to change functionality>
1207 As your application evolves, it may be necessary to modify your schema
1208 to change functionality. Once the changes are made to your schema in
1209 DBIx::Class, export the modified schema and the conversion scripts as
1210 in L</Creating DDL SQL>.
1212 B<Deploy update to customers>
1214 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1215 Schema class. This will add a new table to your database called
1216 C<dbix_class_schema_vesion> which will keep track of which version is installed
1217 and warn if the user trys to run a newer schema version than the
1218 database thinks it has.
1220 Alternatively, you can send the conversion sql scripts to your
1223 =head2 Setting quoting for the generated SQL.
1225 If the database contains column names with spaces and/or reserved words, they
1226 need to be quoted in the SQL queries. This is done using:
1228 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1229 __PACKAGE__->storage->sql_maker->name_sep('.');
1231 The first sets the quote characters. Either a pair of matching
1232 brackets, or a C<"> or C<'>:
1234 __PACKAGE__->storage->sql_maker->quote_char('"');
1236 Check the documentation of your database for the correct quote
1237 characters to use. C<name_sep> needs to be set to allow the SQL
1238 generator to put the quotes the correct place.
1240 In most cases you should set these as part of the arguments passed to
1241 L<DBIx::Class::Schema/conect>:
1243 my $schema = My::Schema->connect(
1253 =head2 Setting limit dialect for SQL::Abstract::Limit
1255 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1256 the remote SQL server by looking at the database handle. This is a
1257 common problem when using the DBD::JDBC, since the DBD-driver only
1258 know that in has a Java-driver available, not which JDBC driver the
1259 Java component has loaded. This specifically sets the limit_dialect
1260 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1263 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1265 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1266 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1268 The limit dialect can also be set at connect time by specifying a
1269 C<limit_dialect> key in the final hash as shown above.
1271 =head1 BOOTSTRAPPING/MIGRATING
1273 =head2 Easy migration from class-based to schema-based setup
1275 You want to start using the schema-based approach to L<DBIx::Class>
1276 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1277 of existing classes that you don't want to move by hand. Try this nifty script
1281 use SQL::Translator;
1283 my $schema = MyDB->schema_instance;
1285 my $translator = SQL::Translator->new(
1286 debug => $debug || 0,
1287 trace => $trace || 0,
1288 no_comments => $no_comments || 0,
1289 show_warnings => $show_warnings || 0,
1290 add_drop_table => $add_drop_table || 0,
1291 validate => $validate || 0,
1293 'DBIx::Schema' => $schema,
1296 'prefix' => 'My::Schema',
1300 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1301 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1303 my $output = $translator->translate(@args) or die
1304 "Error: " . $translator->error;
1308 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1309 namespace, which is currently left as an exercise for the reader.
1311 =head1 OVERLOADING METHODS
1313 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1314 method calls, useful for things like default values and triggers. You have to
1315 use calls to C<next::method> to overload methods. More information on using
1316 L<Class::C3> with L<DBIx::Class> can be found in
1317 L<DBIx::Class::Manual::Component>.
1319 =head2 Setting default values for a row
1321 It's as simple as overriding the C<new> method. Note the use of
1325 my ( $class, $attrs ) = @_;
1327 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1329 my $new = $class->next::method($attrs);
1334 For more information about C<next::method>, look in the L<Class::C3>
1335 documentation. See also L<DBIx::Class::Manual::Component> for more
1336 ways to write your own base classes to do this.
1338 People looking for ways to do "triggers" with DBIx::Class are probably
1339 just looking for this.
1341 =head2 Changing one field whenever another changes
1343 For example, say that you have three columns, C<id>, C<number>, and
1344 C<squared>. You would like to make changes to C<number> and have
1345 C<squared> be automagically set to the value of C<number> squared.
1346 You can accomplish this by overriding C<store_column>:
1349 my ( $self, $name, $value ) = @_;
1350 if ($name eq 'number') {
1351 $self->squared($value * $value);
1353 $self->next::method($name, $value);
1356 Note that the hard work is done by the call to C<next::method>, which
1357 redispatches your call to store_column in the superclass(es).
1359 =head2 Automatically creating related objects
1361 You might have a class C<Artist> which has many C<CD>s. Further, if you
1362 want to create a C<CD> object every time you insert an C<Artist> object.
1363 You can accomplish this by overriding C<insert> on your objects:
1366 my ( $self, @args ) = @_;
1367 $self->next::method(@args);
1368 $self->cds->new({})->fill_from_artist($self)->insert;
1372 where C<fill_from_artist> is a method you specify in C<CD> which sets
1373 values in C<CD> based on the data in the C<Artist> object you pass in.
1375 =head2 Wrapping/overloading a column accessor
1379 Say you have a table "Camera" and want to associate a description
1380 with each camera. For most cameras, you'll be able to generate the description from
1381 the other columns. However, in a few special cases you may want to associate a
1382 custom description with a camera.
1386 In your database schema, define a description field in the "Camera" table that
1387 can contain text and null values.
1389 In DBIC, we'll overload the column accessor to provide a sane default if no
1390 custom description is defined. The accessor will either return or generate the
1391 description, depending on whether the field is null or not.
1393 First, in your "Camera" schema class, define the description field as follows:
1395 __PACKAGE__->add_columns(description => { accessor => '_description' });
1397 Next, we'll define the accessor-wrapper subroutine:
1402 # If there is an update to the column, we'll let the original accessor
1404 return $self->_description(@_) if @_;
1406 # Fetch the column value.
1407 my $description = $self->_description;
1409 # If there's something in the description field, then just return that.
1410 return $description if defined $description && length $descripton;
1412 # Otherwise, generate a description.
1413 return $self->generate_description;
1416 =head1 DEBUGGING AND PROFILING
1418 =head2 DBIx::Class objects with Data::Dumper
1420 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1421 be hard to find the pertinent data in all the data it can generate.
1422 Specifically, if one naively tries to use it like so,
1426 my $cd = $schema->resultset('CD')->find(1);
1429 several pages worth of data from the CD object's schema and result source will
1430 be dumped to the screen. Since usually one is only interested in a few column
1431 values of the object, this is not very helpful.
1433 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1434 it. Simply define a hook that L<Data::Dumper> will call on the object before
1435 dumping it. For example,
1442 result_source => undef,
1450 local $Data::Dumper::Freezer = '_dumper_hook';
1452 my $cd = $schema->resultset('CD')->find(1);
1454 # dumps $cd without its ResultSource
1456 If the structure of your schema is such that there is a common base class for
1457 all your table classes, simply put a method similar to C<_dumper_hook> in the
1458 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1459 will automagically clean up your data before printing it. See
1460 L<Data::Dumper/EXAMPLES> for more information.
1464 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1465 executed as well as notifications of query completion and transaction
1466 begin/commit. If you'd like to profile the SQL you can subclass the
1467 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1470 package My::Profiler;
1473 use base 'DBIx::Class::Storage::Statistics';
1475 use Time::HiRes qw(time);
1484 $self->print("Executing $sql: ".join(', ', @params)."\n");
1493 my $elapsed = sprintf("%0.4f", time() - $start);
1494 $self->print("Execution took $elapsed seconds.\n");
1500 You can then install that class as the debugging object:
1502 __PACKAGE__->storage->debugobj(new My::Profiler());
1503 __PACKAGE__->storage->debug(1);
1505 A more complicated example might involve storing each execution of SQL in an
1513 my $elapsed = time() - $start;
1514 push(@{ $calls{$sql} }, {
1520 You could then create average, high and low execution times for an SQL
1521 statement and dig down to see if certain parameters cause aberrant behavior.
1522 You might want to check out L<DBIx::Class::QueryLog> as well.