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 You can get a L<Data::Page> object for the resultset (suitable for use
23 in e.g. a template) using the C<pager> method:
27 =head2 Complex WHERE clauses
29 Sometimes you need to formulate a query using specific operators:
31 my @albums = $schema->resultset('Album')->search({
32 artist => { 'like', '%Lamb%' },
33 title => { 'like', '%Fear of Fours%' },
36 This results in something like the following C<WHERE> clause:
38 WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
40 Other queries might require slightly more complex logic:
42 my @albums = $schema->resultset('Album')->search({
45 artist => { 'like', '%Smashing Pumpkins%' },
46 title => 'Siamese Dream',
48 artist => 'Starchildren',
52 This results in the following C<WHERE> clause:
54 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
55 OR artist = 'Starchildren'
57 For more information on generating complex queries, see
58 L<SQL::Abstract/WHERE CLAUSES>.
60 =head2 Retrieve one and only one row from a resultset
62 Sometimes you need only the first "top" row of a resultset. While this can be
63 easily done with L<< $rs->first|DBIx::Class::ResultSet/first >>, it is suboptimal,
64 as a full blown cursor for the resultset will be created and then immediately
65 destroyed after fetching the first row object.
66 L<< $rs->single|DBIx::Class::ResultSet/single >> is
67 designed specifically for this case - it will grab the first returned result
68 without even instantiating a cursor.
70 Before replacing all your calls to C<first()> with C<single()> please observe the
76 While single() takes a search condition just like search() does, it does
77 _not_ accept search attributes. However one can always chain a single() to
80 my $top_cd = $cd_rs -> search({}, { order_by => 'rating' }) -> single;
84 Since single() is the engine behind find(), it is designed to fetch a
85 single row per database query. Thus a warning will be issued when the
86 underlying SELECT returns more than one row. Sometimes however this usage
87 is valid: i.e. we have an arbitrary number of cd's but only one of them is
88 at the top of the charts at any given time. If you know what you are doing,
89 you can silence the warning by explicitly limiting the resultset size:
91 my $top_cd = $cd_rs -> search ({}, { order_by => 'rating', rows => 1 }) -> single;
95 =head2 Arbitrary SQL through a custom ResultSource
97 Sometimes you have to run arbitrary SQL because your query is too complex
98 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
99 be optimized for your database in a special way, but you still want to
100 get the results as a L<DBIx::Class::ResultSet>.
101 The recommended way to accomplish this is by defining a separate ResultSource
102 for your query. You can then inject complete SQL statements using a scalar
103 reference (this is a feature of L<SQL::Abstract>).
105 Say you want to run a complex custom query on your user data, here's what
106 you have to add to your User class:
108 package My::Schema::Result::User;
110 use base qw/DBIx::Class/;
112 # ->load_components, ->table, ->add_columns, etc.
114 # Make a new ResultSource based on the User class
115 my $source = __PACKAGE__->result_source_instance();
116 my $new_source = $source->new( $source );
117 $new_source->source_name( 'UserFriendsComplex' );
119 # Hand in your query as a scalar reference
120 # It will be added as a sub-select after FROM,
121 # so pay attention to the surrounding brackets!
122 $new_source->name( \<<SQL );
123 ( SELECT u.* FROM user u
124 INNER JOIN user_friends f ON u.id = f.user_id
125 WHERE f.friend_user_id = ?
127 SELECT u.* FROM user u
128 INNER JOIN user_friends f ON u.id = f.friend_user_id
129 WHERE f.user_id = ? )
132 # Finally, register your new ResultSource with your Schema
133 My::Schema->register_extra_source( 'UserFriendsComplex' => $new_source );
135 Next, you can execute your complex query using bind parameters like this:
137 my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {},
139 bind => [ 12345, 12345 ]
143 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
144 that you cannot modify the rows it contains, ie. cannot call L</update>,
145 L</delete>, ... on it).
147 If you prefer to have the definitions of these custom ResultSources in separate
148 files (instead of stuffing all of them into the same resultset class), you can
149 achieve the same with subclassing the resultset class and defining the
152 package My::Schema::Result::UserFriendsComplex;
154 use My::Schema::Result::User;
155 use base qw/My::Schema::Result::User/;
157 __PACKAGE__->table('dummy'); # currently must be called before anything else
159 # Hand in your query as a scalar reference
160 # It will be added as a sub-select after FROM,
161 # so pay attention to the surrounding brackets!
162 __PACKAGE__->name( \<<SQL );
163 ( SELECT u.* FROM user u
164 INNER JOIN user_friends f ON u.id = f.user_id
165 WHERE f.friend_user_id = ?
167 SELECT u.* FROM user u
168 INNER JOIN user_friends f ON u.id = f.friend_user_id
169 WHERE f.user_id = ? )
174 =head2 Using specific columns
176 When you only want specific columns from a table, you can use
177 C<columns> to specify which ones you need. This is useful to avoid
178 loading columns with large amounts of data that you aren't about to
181 my $rs = $schema->resultset('Artist')->search(
184 columns => [qw/ name /]
189 # SELECT artist.name FROM artist
191 This is a shortcut for C<select> and C<as>, see below. C<columns>
192 cannot be used together with C<select> and C<as>.
194 =head2 Using database functions or stored procedures
196 The combination of C<select> and C<as> can be used to return the result of a
197 database function or stored procedure as a column value. You use C<select> to
198 specify the source for your column value (e.g. a column name, function, or
199 stored procedure name). You then use C<as> to set the column name you will use
200 to access the returned value:
202 my $rs = $schema->resultset('Artist')->search(
205 select => [ 'name', { LENGTH => 'name' } ],
206 as => [qw/ name name_length /],
211 # SELECT name name, LENGTH( name )
214 Note that the C< as > attribute has absolutely nothing to with the sql
215 syntax C< SELECT foo AS bar > (see the documentation in
216 L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
217 column in your base class (i.e. it was added with C<add_columns>), you
218 just access it as normal. Our C<Artist> class has a C<name> column, so
219 we just use the C<name> accessor:
221 my $artist = $rs->first();
222 my $name = $artist->name();
224 If on the other hand the alias does not correspond to an existing column, you
225 have to fetch the value using the C<get_column> accessor:
227 my $name_length = $artist->get_column('name_length');
229 If you don't like using C<get_column>, you can always create an accessor for
230 any of your aliases using either of these:
232 # Define accessor manually:
233 sub name_length { shift->get_column('name_length'); }
235 # Or use DBIx::Class::AccessorGroup:
236 __PACKAGE__->mk_group_accessors('column' => 'name_length');
238 =head2 SELECT DISTINCT with multiple columns
240 my $rs = $schema->resultset('Artist')->search(
243 columns => [ qw/artist_id name rank/ ],
248 my $rs = $schema->resultset('Artist')->search(
251 columns => [ qw/artist_id name rank/ ],
252 group_by => [ qw/artist_id name rank/ ],
257 # SELECT me.artist_id, me.name, me.rank
259 # GROUP BY artist_id, name, rank
261 =head2 SELECT COUNT(DISTINCT colname)
263 my $rs = $schema->resultset('Artist')->search(
266 columns => [ qw/name/ ],
271 my $rs = $schema->resultset('Artist')->search(
274 columns => [ qw/name/ ],
275 group_by => [ qw/name/ ],
279 my $count = $rs->count;
282 # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) count_subq:
284 =head2 Grouping results
286 L<DBIx::Class> supports C<GROUP BY> as follows:
288 my $rs = $schema->resultset('Artist')->search(
292 select => [ 'name', { count => 'cds.id' } ],
293 as => [qw/ name cd_count /],
294 group_by => [qw/ name /]
299 # SELECT name, COUNT( cd.id ) FROM artist
300 # LEFT JOIN cd ON artist.id = cd.artist
303 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
304 are in any way unsure about the use of the attributes above (C< join
305 >, C< select >, C< as > and C< group_by >).
307 =head2 Subqueries (EXPERIMENTAL)
309 You can write subqueries relatively easily in DBIC.
311 my $inside_rs = $schema->resultset('Artist')->search({
312 name => [ 'Billy Joel', 'Brittany Spears' ],
315 my $rs = $schema->resultset('CD')->search({
316 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
319 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
321 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
322 The following will B<not> work:
324 my $rs = $schema->resultset('CD')->search({
325 artist_id => $inside_rs->get_column('id')->as_query,
330 Subqueries are supported in the where clause (first hashref), and in the
331 from, select, and +select attributes.
333 =head3 Correlated subqueries
335 my $cdrs = $schema->resultset('CD');
336 my $rs = $cdrs->search({
338 '=' => $cdrs->search(
339 { artist_id => { '=' => \'me.artist_id' } },
341 )->get_column('year')->max_rs->as_query,
345 That creates the following SQL:
347 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
350 SELECT MAX(inner.year)
352 WHERE artist_id = me.artist_id
357 Please note that subqueries are considered an experimental feature.
359 =head2 Predefined searches
361 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
362 and define often used searches as methods:
364 package My::DBIC::ResultSet::CD;
367 use base 'DBIx::Class::ResultSet';
369 sub search_cds_ordered {
372 return $self->search(
374 { order_by => 'name DESC' },
380 To use your resultset, first tell DBIx::Class to create an instance of it
381 for you, in your My::DBIC::Schema::CD class:
383 # class definition as normal
384 __PACKAGE__->load_components(qw/ Core /);
385 __PACKAGE__->table('cd');
387 # tell DBIC to use the custom ResultSet class
388 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
390 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
392 Then call your new method in your code:
394 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
396 =head2 Using SQL functions on the left hand side of a comparison
398 Using SQL functions on the left hand side of a comparison is generally
399 not a good idea since it requires a scan of the entire table. However,
400 it can be accomplished with C<DBIx::Class> when necessary.
402 If you do not have quoting on, simply include the function in your search
403 specification as you would any column:
405 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
407 With quoting on, or for a more portable solution, use the C<where>
410 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
414 (When the bind args ordering bug is fixed, this technique will be better
415 and can replace the one above.)
417 With quoting on, or for a more portable solution, use the C<where> and
421 where => \'YEAR(date_of_birth) = ?',
427 =head1 JOINS AND PREFETCHING
429 =head2 Using joins and prefetch
431 You can use the C<join> attribute to allow searching on, or sorting your
432 results by, one or more columns in a related table.
434 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
436 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
438 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
440 my $rs = $schema->resultset('CD')->search(
442 'artists.name' => 'Bob Marley'
445 join => 'artists', # join the artist table
450 # SELECT cd.* FROM cd
451 # JOIN artist ON cd.artist = artist.id
452 # WHERE artist.name = 'Bob Marley'
454 In that example both the join, and the condition use the relationship name rather than the table name
455 (see DBIx::Class::Manual::Joining for more details on aliasing ).
457 If required, you can now sort on any column in the related tables by including
458 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
460 my $rs = $schema->resultset('CD')->search(
462 'artists.name' => 'Bob Marley'
466 order_by => [qw/ artists.name /]
471 # SELECT cd.* FROM cd
472 # JOIN artist ON cd.artist = artist.id
473 # WHERE artist.name = 'Bob Marley'
474 # ORDER BY artist.name
476 Note that the C<join> attribute should only be used when you need to search or
477 sort using columns in a related table. Joining related tables when you only
478 need columns from the main table will make performance worse!
480 Now let's say you want to display a list of CDs, each with the name of the
481 artist. The following will work fine:
483 while (my $cd = $rs->next) {
484 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
487 There is a problem however. We have searched both the C<cd> and C<artist> tables
488 in our main query, but we have only returned data from the C<cd> table. To get
489 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
492 SELECT artist.* FROM artist WHERE artist.id = ?
494 A statement like the one above will run for each and every CD returned by our
495 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
498 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
499 This allows you to fetch results from related tables in advance:
501 my $rs = $schema->resultset('CD')->search(
503 'artists.name' => 'Bob Marley'
507 order_by => [qw/ artists.name /],
508 prefetch => 'artists' # return artist data too!
512 # Equivalent SQL (note SELECT from both "cd" and "artist"):
513 # SELECT cd.*, artist.* FROM cd
514 # JOIN artist ON cd.artist = artist.id
515 # WHERE artist.name = 'Bob Marley'
516 # ORDER BY artist.name
518 The code to print the CD list remains the same:
520 while (my $cd = $rs->next) {
521 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
524 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
525 so no additional SQL statements are executed. You now have a much more
528 Also note that C<prefetch> should only be used when you know you will
529 definitely use data from a related table. Pre-fetching related tables when you
530 only need columns from the main table will make performance worse!
532 =head2 Multiple joins
534 In the examples above, the C<join> attribute was a scalar. If you
535 pass an array reference instead, you can join to multiple tables. In
536 this example, we want to limit the search further, using
539 # Relationships defined elsewhere:
540 # CD->belongs_to('artist' => 'Artist');
541 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
542 my $rs = $schema->resultset('CD')->search(
544 'artist.name' => 'Bob Marley'
545 'liner_notes.notes' => { 'like', '%some text%' },
548 join => [qw/ artist liner_notes /],
549 order_by => [qw/ artist.name /],
554 # SELECT cd.*, artist.*, liner_notes.* FROM cd
555 # JOIN artist ON cd.artist = artist.id
556 # JOIN liner_notes ON cd.id = liner_notes.cd
557 # WHERE artist.name = 'Bob Marley'
558 # ORDER BY artist.name
560 =head2 Multi-step joins
562 Sometimes you want to join more than one relationship deep. In this example,
563 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
564 contain a specific string:
566 # Relationships defined elsewhere:
567 # Artist->has_many('cds' => 'CD', 'artist');
568 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
570 my $rs = $schema->resultset('Artist')->search(
572 'liner_notes.notes' => { 'like', '%some text%' },
576 'cds' => 'liner_notes'
582 # SELECT artist.* FROM artist
583 # LEFT JOIN cd ON artist.id = cd.artist
584 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
585 # WHERE liner_notes.notes LIKE '%some text%'
587 Joins can be nested to an arbitrary level. So if we decide later that we
588 want to reduce the number of Artists returned based on who wrote the liner
591 # Relationship defined elsewhere:
592 # LinerNotes->belongs_to('author' => 'Person');
594 my $rs = $schema->resultset('Artist')->search(
596 'liner_notes.notes' => { 'like', '%some text%' },
597 'author.name' => 'A. Writer'
602 'liner_notes' => 'author'
609 # SELECT artist.* FROM artist
610 # LEFT JOIN cd ON artist.id = cd.artist
611 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
612 # LEFT JOIN author ON author.id = liner_notes.author
613 # WHERE liner_notes.notes LIKE '%some text%'
614 # AND author.name = 'A. Writer'
616 =head2 Multi-step and multiple joins
618 With various combinations of array and hash references, you can join
619 tables in any combination you desire. For example, to join Artist to
620 CD and Concert, and join CD to LinerNotes:
622 # Relationships defined elsewhere:
623 # Artist->has_many('concerts' => 'Concert', 'artist');
625 my $rs = $schema->resultset('Artist')->search(
638 # SELECT artist.* FROM artist
639 # LEFT JOIN cd ON artist.id = cd.artist
640 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
641 # LEFT JOIN concert ON artist.id = concert.artist
643 =head2 Multi-step prefetch
645 C<prefetch> can be nested more than one relationship
646 deep using the same syntax as a multi-step join:
648 my $rs = $schema->resultset('Tag')->search(
658 # SELECT tag.*, cd.*, artist.* FROM tag
659 # JOIN cd ON tag.cd = cd.id
660 # JOIN artist ON cd.artist = artist.id
662 Now accessing our C<cd> and C<artist> relationships does not need additional
665 my $tag = $rs->first;
666 print $tag->cd->artist->name;
668 =head1 ROW-LEVEL OPERATIONS
670 =head2 Retrieving a row object's Schema
672 It is possible to get a Schema object from a row object like so:
674 my $schema = $cd->result_source->schema;
675 # use the schema as normal:
676 my $artist_rs = $schema->resultset('Artist');
678 This can be useful when you don't want to pass around a Schema object to every
681 =head2 Getting the value of the primary key for the last database insert
683 AKA getting last_insert_id
685 Thanks to the core component PK::Auto, this is straightforward:
687 my $foo = $rs->create(\%blah);
689 my $id = $foo->id; # foo->my_primary_key_field will also work.
691 If you are not using autoincrementing primary keys, this will probably
692 not work, but then you already know the value of the last primary key anyway.
694 =head2 Stringification
696 Employ the standard stringification technique by using the C<overload>
699 To make an object stringify itself as a single column, use something
700 like this (replace C<name> with the column/method of your choice):
702 use overload '""' => sub { shift->name}, fallback => 1;
704 For more complex stringification, you can use an anonymous subroutine:
706 use overload '""' => sub { $_[0]->name . ", " .
707 $_[0]->address }, fallback => 1;
709 =head3 Stringification Example
711 Suppose we have two tables: C<Product> and C<Category>. The table
714 Product(id, Description, category)
715 Category(id, Description)
717 C<category> is a foreign key into the Category table.
719 If you have a Product object C<$obj> and write something like
723 things will not work as expected.
725 To obtain, for example, the category description, you should add this
726 method to the class defining the Category table:
728 use overload "" => sub {
731 return $self->Description;
734 =head2 Want to know if find_or_create found or created a row?
736 Just use C<find_or_new> instead, then check C<in_storage>:
738 my $obj = $rs->find_or_new({ blah => 'blarg' });
739 unless ($obj->in_storage) {
741 # do whatever else you wanted if it was a new row
744 =head2 Static sub-classing DBIx::Class result classes
746 AKA adding additional relationships/methods/etc. to a model for a
747 specific usage of the (shared) model.
751 package My::App::Schema;
753 use base DBIx::Class::Schema;
755 # load subclassed classes from My::App::Schema::Result/ResultSet
756 __PACKAGE__->load_namespaces;
758 # load classes from shared model
760 'My::Shared::Model::Result' => [qw/
767 B<Result-Subclass definition>
769 package My::App::Schema::Result::Baz;
773 use base My::Shared::Model::Result::Baz;
775 # WARNING: Make sure you call table() again in your subclass,
776 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
777 # and the class name is not correctly registered as a source
778 __PACKAGE__->table('baz');
780 sub additional_method {
781 return "I'm an additional method only needed by this app";
786 =head2 Dynamic Sub-classing DBIx::Class proxy classes
788 AKA multi-class object inflation from one table
790 L<DBIx::Class> classes are proxy classes, therefore some different
791 techniques need to be employed for more than basic subclassing. In
792 this example we have a single user table that carries a boolean bit
793 for admin. We would like like to give the admin users
794 objects(L<DBIx::Class::Row>) the same methods as a regular user but
795 also special admin only methods. It doesn't make sense to create two
796 seperate proxy-class files for this. We would be copying all the user
797 methods into the Admin class. There is a cleaner way to accomplish
800 Overriding the C<inflate_result> method within the User proxy-class
801 gives us the effect we want. This method is called by
802 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
803 grab the object being returned, inspect the values we are looking for,
804 bless it if it's an admin object, and then return it. See the example
811 use base qw/DBIx::Class::Schema/;
813 __PACKAGE__->load_namespaces;
818 B<Proxy-Class definitions>
820 package My::Schema::Result::User;
824 use base qw/DBIx::Class/;
826 ### Defined what our admin class is for ensure_class_loaded
827 my $admin_class = __PACKAGE__ . '::Admin';
829 __PACKAGE__->load_components(qw/Core/);
831 __PACKAGE__->table('users');
833 __PACKAGE__->add_columns(qw/user_id email password
834 firstname lastname active
837 __PACKAGE__->set_primary_key('user_id');
841 my $ret = $self->next::method(@_);
842 if( $ret->admin ) {### If this is an admin rebless for extra functions
843 $self->ensure_class_loaded( $admin_class );
844 bless $ret, $admin_class;
850 print "I am a regular user.\n";
857 package My::Schema::Result::User::Admin;
861 use base qw/My::Schema::Result::User/;
865 print "I am an admin.\n";
871 print "I am doing admin stuff\n";
883 my $user_data = { email => 'someguy@place.com',
887 my $admin_data = { email => 'someadmin@adminplace.com',
891 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
893 $schema->resultset('User')->create( $user_data );
894 $schema->resultset('User')->create( $admin_data );
896 ### Now we search for them
897 my $user = $schema->resultset('User')->single( $user_data );
898 my $admin = $schema->resultset('User')->single( $admin_data );
900 print ref $user, "\n";
901 print ref $admin, "\n";
903 print $user->password , "\n"; # pass1
904 print $admin->password , "\n";# pass2; inherited from User
905 print $user->hello , "\n";# I am a regular user.
906 print $admin->hello, "\n";# I am an admin.
908 ### The statement below will NOT print
909 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
910 ### The statement below will print
911 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
913 =head2 Skip row object creation for faster results
915 DBIx::Class is not built for speed, it's built for convenience and
916 ease of use, but sometimes you just need to get the data, and skip the
919 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
921 my $rs = $schema->resultset('CD');
923 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
925 my $hash_ref = $rs->find(1);
929 Beware, changing the Result class using
930 L<DBIx::Class::ResultSet/result_class> will replace any existing class
931 completely including any special components loaded using
932 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
934 =head2 Get raw data for blindingly fast results
936 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
937 above is not fast enough for you, you can use a DBIx::Class to return values
938 exactly as they come out of the database with none of the convenience methods
941 This is used like so:
943 my $cursor = $rs->cursor
944 while (my @vals = $cursor->next) {
945 # use $val[0..n] here
948 You will need to map the array offsets to particular columns (you can
949 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
951 =head1 RESULTSET OPERATIONS
953 =head2 Getting Schema from a ResultSet
955 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
957 $rs->result_source->schema
959 =head2 Getting Columns Of Data
963 If you want to find the sum of a particular column there are several
964 ways, the obvious one is to use search:
966 my $rs = $schema->resultset('Items')->search(
969 select => [ { sum => 'Cost' } ],
970 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
973 my $tc = $rs->first->get_column('total_cost');
975 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
976 returned when you ask the C<ResultSet> for a column using
979 my $cost = $schema->resultset('Items')->get_column('Cost');
982 With this you can also do:
984 my $minvalue = $cost->min;
985 my $maxvalue = $cost->max;
987 Or just iterate through the values of this column only:
989 while ( my $c = $cost->next ) {
993 foreach my $c ($cost->all) {
997 C<ResultSetColumn> only has a limited number of built-in functions, if
998 you need one that it doesn't have, then you can use the C<func> method
1001 my $avg = $cost->func('AVERAGE');
1003 This will cause the following SQL statement to be run:
1005 SELECT AVERAGE(Cost) FROM Items me
1007 Which will of course only work if your database supports this function.
1008 See L<DBIx::Class::ResultSetColumn> for more documentation.
1010 =head2 Creating a result set from a set of rows
1012 Sometimes you have a (set of) row objects that you want to put into a
1013 resultset without the need to hit the DB again. You can do that by using the
1014 L<set_cache|DBIx::Class::Resultset/set_cache> method:
1016 my @uploadable_groups;
1017 while (my $group = $groups->next) {
1018 if ($group->can_upload($self)) {
1019 push @uploadable_groups, $group;
1022 my $new_rs = $self->result_source->resultset;
1023 $new_rs->set_cache(\@uploadable_groups);
1027 =head1 USING RELATIONSHIPS
1029 =head2 Create a new row in a related table
1031 my $author = $book->create_related('author', { name => 'Fred'});
1033 =head2 Search in a related table
1035 Only searches for books named 'Titanic' by the author in $author.
1037 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1039 =head2 Delete data in a related table
1041 Deletes only the book named Titanic by the author in $author.
1043 $author->delete_related('books', { name => 'Titanic' });
1045 =head2 Ordering a relationship result set
1047 If you always want a relation to be ordered, you can specify this when you
1048 create the relationship.
1050 To order C<< $book->pages >> by descending page_number, create the relation
1053 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
1055 =head2 Filtering a relationship result set
1057 If you want to get a filtered result set, you can just add add to $attr as follows:
1059 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1061 =head2 Many-to-many relationships
1063 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1066 use base 'DBIx::Class';
1067 __PACKAGE__->load_components('Core');
1068 __PACKAGE__->table('user');
1069 __PACKAGE__->add_columns(qw/id name/);
1070 __PACKAGE__->set_primary_key('id');
1071 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1072 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1074 package My::UserAddress;
1075 use base 'DBIx::Class';
1076 __PACKAGE__->load_components('Core');
1077 __PACKAGE__->table('user_address');
1078 __PACKAGE__->add_columns(qw/user address/);
1079 __PACKAGE__->set_primary_key(qw/user address/);
1080 __PACKAGE__->belongs_to('user' => 'My::User');
1081 __PACKAGE__->belongs_to('address' => 'My::Address');
1083 package My::Address;
1084 use base 'DBIx::Class';
1085 __PACKAGE__->load_components('Core');
1086 __PACKAGE__->table('address');
1087 __PACKAGE__->add_columns(qw/id street town area_code country/);
1088 __PACKAGE__->set_primary_key('id');
1089 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1090 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1092 $rs = $user->addresses(); # get all addresses for a user
1093 $rs = $address->users(); # get all users for an address
1095 =head2 Relationships across DB schemas
1097 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1098 is easy as long as the schemas themselves are all accessible via the same DBI
1099 connection. In most cases, this means that they are on the same database host
1100 as each other and your connecting database user has the proper permissions to them.
1102 To accomplish this one only needs to specify the DB schema name in the table
1103 declaration, like so...
1105 package MyDatabase::Main::Artist;
1106 use base qw/DBIx::Class/;
1107 __PACKAGE__->load_components(qw/PK::Auto Core/);
1109 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1111 __PACKAGE__->add_columns(qw/ artist_id name /);
1112 __PACKAGE__->set_primary_key('artist_id');
1113 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1117 Whatever string you specify there will be used to build the "FROM" clause in SQL
1120 The big drawback to this is you now have DB schema names hardcoded in your
1121 class files. This becomes especially troublesome if you have multiple instances
1122 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1123 the DB schemas are named based on the environment (e.g. database1_dev).
1125 However, one can dynamically "map" to the proper DB schema by overriding the
1126 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1127 building a renaming facility, like so:
1129 package MyDatabase::Schema;
1132 extends 'DBIx::Class::Schema';
1134 around connection => sub {
1135 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1137 my $postfix = delete $attr->{schema_name_postfix};
1142 $self->append_db_name($postfix);
1146 sub append_db_name {
1147 my ( $self, $postfix ) = @_;
1151 { $_->name =~ /^\w+\./mx }
1153 { $self->source($_) }
1156 foreach my $source (@sources_with_db) {
1157 my $name = $source->name;
1158 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1160 $source->name($name);
1166 By overridding the L<connection|DBIx::Class::Schama/connection>
1167 method and extracting a custom option from the provided \%attr hashref one can
1168 then simply iterate over all the Schema's ResultSources, renaming them as
1171 To use this facility, simply add or modify the \%attr hashref that is passed to
1172 L<connection|DBIx::Class::Schama/connect>, as follows:
1175 = MyDatabase::Schema->connect(
1180 schema_name_postfix => '_dev'
1181 # ... Other options as desired ...
1184 Obviously, one could accomplish even more advanced mapping via a hash map or a
1189 As of version 0.04001, there is improved transaction support in
1190 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1191 example of the recommended way to use it:
1193 my $genus = $schema->resultset('Genus')->find(12);
1195 my $coderef2 = sub {
1200 my $coderef1 = sub {
1201 $genus->add_to_species({ name => 'troglodyte' });
1204 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1205 return $genus->species;
1210 $rs = $schema->txn_do($coderef1);
1213 if ($@) { # Transaction failed
1214 die "the sky is falling!" #
1215 if ($@ =~ /Rollback failed/); # Rollback failed
1217 deal_with_failed_transaction();
1220 Nested transactions will work as expected. That is, only the outermost
1221 transaction will actually issue a commit to the $dbh, and a rollback
1222 at any level of any transaction will cause the entire nested
1223 transaction to fail. Support for savepoints and for true nested
1224 transactions (for databases that support them) will hopefully be added
1229 =head2 Creating Schemas From An Existing Database
1231 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1232 L<DBIx::Class::Schema> and associated sources by examining the database.
1234 The recommend way of achieving this is to use the
1235 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1237 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1238 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1240 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1241 source definitions for all the tables found in the C<foo> database.
1243 =head2 Creating DDL SQL
1245 The following functionality requires you to have L<SQL::Translator>
1246 (also known as "SQL Fairy") installed.
1248 To create a set of database-specific .sql files for the above schema:
1250 my $schema = My::Schema->connect($dsn);
1251 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1256 By default this will create schema files in the current directory, for
1257 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1259 To create a new database using the schema:
1261 my $schema = My::Schema->connect($dsn);
1262 $schema->deploy({ add_drop_tables => 1});
1264 To import created .sql files using the mysql client:
1266 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1268 To create C<ALTER TABLE> conversion scripts to update a database to a
1269 newer version of your schema at a later point, first set a new
1270 C<$VERSION> in your Schema file, then:
1272 my $schema = My::Schema->connect($dsn);
1273 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1279 This will produce new database-specific .sql files for the new version
1280 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1281 requires that the files for 0.1 as created above are available in the
1282 given directory to diff against.
1284 =head2 Select from dual
1286 Dummy tables are needed by some databases to allow calling functions
1287 or expressions that aren't based on table content, for examples of how
1288 this applies to various database types, see:
1289 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1291 Note: If you're using Oracles dual table don't B<ever> do anything
1292 other than a select, if you CRUD on your dual table you *will* break
1295 Make a table class as you would for any other table
1297 package MyAppDB::Dual;
1300 use base 'DBIx::Class';
1301 __PACKAGE__->load_components("Core");
1302 __PACKAGE__->table("Dual");
1303 __PACKAGE__->add_columns(
1305 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1308 Once you've loaded your table class select from it using C<select>
1309 and C<as> instead of C<columns>
1311 my $rs = $schema->resultset('Dual')->search(undef,
1312 { select => [ 'sydate' ],
1317 All you have to do now is be careful how you access your resultset, the below
1318 will not work because there is no column called 'now' in the Dual table class
1320 while (my $dual = $rs->next) {
1321 print $dual->now."\n";
1323 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1325 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1326 your Dual class for whatever you wanted to select from dual, but that's just
1327 silly, instead use C<get_column>
1329 while (my $dual = $rs->next) {
1330 print $dual->get_column('now')."\n";
1335 my $cursor = $rs->cursor;
1336 while (my @vals = $cursor->next) {
1337 print $vals[0]."\n";
1340 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1341 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1342 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1343 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1344 L<SQL::Translator> to not create table dual:
1347 add_drop_table => 1,
1348 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1350 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1352 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1354 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1355 while ( my $dual = $rs->next ) {
1356 print $dual->{now}."\n";
1359 Here are some example C<select> conditions to illustrate the different syntax
1360 you could use for doing stuff like
1361 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1363 # get a sequence value
1364 select => [ 'A_SEQ.nextval' ],
1366 # get create table sql
1367 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1369 # get a random num between 0 and 100
1370 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1373 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1376 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1378 # which day of the week were you born on?
1379 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1381 # select 16 rows from dual
1382 select => [ "'hello'" ],
1384 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1388 =head2 Adding Indexes And Functions To Your SQL
1390 Often you will want indexes on columns on your table to speed up searching. To
1391 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1392 class (refer to the advanced
1393 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1394 to share a hook between multiple sources):
1396 package My::Schema::Result::Artist;
1398 __PACKAGE__->table('artist');
1399 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1401 sub sqlt_deploy_hook {
1402 my ($self, $sqlt_table) = @_;
1404 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1409 Sometimes you might want to change the index depending on the type of the
1410 database for which SQL is being generated:
1412 my ($db_type = $sqlt_table->schema->translator->producer_type)
1413 =~ s/^SQL::Translator::Producer:://;
1415 You can also add hooks to the schema level to stop certain tables being
1422 sub sqlt_deploy_hook {
1423 my ($self, $sqlt_schema) = @_;
1425 $sqlt_schema->drop_table('table_name');
1428 You could also add views, procedures or triggers to the output using
1429 L<SQL::Translator::Schema/add_view>,
1430 L<SQL::Translator::Schema/add_procedure> or
1431 L<SQL::Translator::Schema/add_trigger>.
1434 =head2 Schema versioning
1436 The following example shows simplistically how you might use DBIx::Class to
1437 deploy versioned schemas to your customers. The basic process is as follows:
1443 Create a DBIx::Class schema
1455 Modify schema to change functionality
1459 Deploy update to customers
1463 B<Create a DBIx::Class schema>
1465 This can either be done manually, or generated from an existing database as
1466 described under L</Creating Schemas From An Existing Database>
1470 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1472 B<Deploy to customers>
1474 There are several ways you could deploy your schema. These are probably
1475 beyond the scope of this recipe, but might include:
1481 Require customer to apply manually using their RDBMS.
1485 Package along with your app, making database dump/schema update/tests
1486 all part of your install.
1490 B<Modify the schema to change functionality>
1492 As your application evolves, it may be necessary to modify your schema
1493 to change functionality. Once the changes are made to your schema in
1494 DBIx::Class, export the modified schema and the conversion scripts as
1495 in L</Creating DDL SQL>.
1497 B<Deploy update to customers>
1499 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1500 Schema class. This will add a new table to your database called
1501 C<dbix_class_schema_vesion> which will keep track of which version is installed
1502 and warn if the user trys to run a newer schema version than the
1503 database thinks it has.
1505 Alternatively, you can send the conversion sql scripts to your
1508 =head2 Setting quoting for the generated SQL.
1510 If the database contains column names with spaces and/or reserved words, they
1511 need to be quoted in the SQL queries. This is done using:
1513 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1514 __PACKAGE__->storage->sql_maker->name_sep('.');
1516 The first sets the quote characters. Either a pair of matching
1517 brackets, or a C<"> or C<'>:
1519 __PACKAGE__->storage->sql_maker->quote_char('"');
1521 Check the documentation of your database for the correct quote
1522 characters to use. C<name_sep> needs to be set to allow the SQL
1523 generator to put the quotes the correct place.
1525 In most cases you should set these as part of the arguments passed to
1526 L<DBIx::Class::Schema/connect>:
1528 my $schema = My::Schema->connect(
1538 =head2 Setting limit dialect for SQL::Abstract::Limit
1540 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1541 the remote SQL server by looking at the database handle. This is a
1542 common problem when using the DBD::JDBC, since the DBD-driver only
1543 know that in has a Java-driver available, not which JDBC driver the
1544 Java component has loaded. This specifically sets the limit_dialect
1545 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1548 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1550 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1551 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1553 The limit dialect can also be set at connect time by specifying a
1554 C<limit_dialect> key in the final hash as shown above.
1556 =head2 Working with PostgreSQL array types
1558 You can also assign values to PostgreSQL array columns by passing array
1559 references in the C<\%columns> (C<\%vals>) hashref of the
1560 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1563 $resultset->create({
1564 numbers => [1, 2, 3]
1569 numbers => [1, 2, 3]
1576 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1577 methods) you cannot directly use array references (since this is interpreted as
1578 a list of values to be C<OR>ed), but you can use the following syntax to force
1579 passing them as bind values:
1583 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1587 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1588 placeholders and bind values (subqueries)> for more explanation. Note that
1589 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1590 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1591 arrayrefs together with the column name, like this: C<< [column_name => value]
1594 =head1 BOOTSTRAPPING/MIGRATING
1596 =head2 Easy migration from class-based to schema-based setup
1598 You want to start using the schema-based approach to L<DBIx::Class>
1599 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1600 of existing classes that you don't want to move by hand. Try this nifty script
1604 use SQL::Translator;
1606 my $schema = MyDB->schema_instance;
1608 my $translator = SQL::Translator->new(
1609 debug => $debug || 0,
1610 trace => $trace || 0,
1611 no_comments => $no_comments || 0,
1612 show_warnings => $show_warnings || 0,
1613 add_drop_table => $add_drop_table || 0,
1614 validate => $validate || 0,
1616 'DBIx::Schema' => $schema,
1619 'prefix' => 'My::Schema',
1623 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1624 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1626 my $output = $translator->translate(@args) or die
1627 "Error: " . $translator->error;
1631 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1632 namespace, which is currently left as an exercise for the reader.
1634 =head1 OVERLOADING METHODS
1636 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1637 method calls, useful for things like default values and triggers. You have to
1638 use calls to C<next::method> to overload methods. More information on using
1639 L<Class::C3> with L<DBIx::Class> can be found in
1640 L<DBIx::Class::Manual::Component>.
1642 =head2 Setting default values for a row
1644 It's as simple as overriding the C<new> method. Note the use of
1648 my ( $class, $attrs ) = @_;
1650 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1652 my $new = $class->next::method($attrs);
1657 For more information about C<next::method>, look in the L<Class::C3>
1658 documentation. See also L<DBIx::Class::Manual::Component> for more
1659 ways to write your own base classes to do this.
1661 People looking for ways to do "triggers" with DBIx::Class are probably
1662 just looking for this.
1664 =head2 Changing one field whenever another changes
1666 For example, say that you have three columns, C<id>, C<number>, and
1667 C<squared>. You would like to make changes to C<number> and have
1668 C<squared> be automagically set to the value of C<number> squared.
1669 You can accomplish this by overriding C<store_column>:
1672 my ( $self, $name, $value ) = @_;
1673 if ($name eq 'number') {
1674 $self->squared($value * $value);
1676 $self->next::method($name, $value);
1679 Note that the hard work is done by the call to C<next::method>, which
1680 redispatches your call to store_column in the superclass(es).
1682 =head2 Automatically creating related objects
1684 You might have a class C<Artist> which has many C<CD>s. Further, if you
1685 want to create a C<CD> object every time you insert an C<Artist> object.
1686 You can accomplish this by overriding C<insert> on your objects:
1689 my ( $self, @args ) = @_;
1690 $self->next::method(@args);
1691 $self->cds->new({})->fill_from_artist($self)->insert;
1695 where C<fill_from_artist> is a method you specify in C<CD> which sets
1696 values in C<CD> based on the data in the C<Artist> object you pass in.
1698 =head2 Wrapping/overloading a column accessor
1702 Say you have a table "Camera" and want to associate a description
1703 with each camera. For most cameras, you'll be able to generate the description from
1704 the other columns. However, in a few special cases you may want to associate a
1705 custom description with a camera.
1709 In your database schema, define a description field in the "Camera" table that
1710 can contain text and null values.
1712 In DBIC, we'll overload the column accessor to provide a sane default if no
1713 custom description is defined. The accessor will either return or generate the
1714 description, depending on whether the field is null or not.
1716 First, in your "Camera" schema class, define the description field as follows:
1718 __PACKAGE__->add_columns(description => { accessor => '_description' });
1720 Next, we'll define the accessor-wrapper subroutine:
1725 # If there is an update to the column, we'll let the original accessor
1727 return $self->_description(@_) if @_;
1729 # Fetch the column value.
1730 my $description = $self->_description;
1732 # If there's something in the description field, then just return that.
1733 return $description if defined $description && length $descripton;
1735 # Otherwise, generate a description.
1736 return $self->generate_description;
1739 =head1 DEBUGGING AND PROFILING
1741 =head2 DBIx::Class objects with Data::Dumper
1743 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1744 be hard to find the pertinent data in all the data it can generate.
1745 Specifically, if one naively tries to use it like so,
1749 my $cd = $schema->resultset('CD')->find(1);
1752 several pages worth of data from the CD object's schema and result source will
1753 be dumped to the screen. Since usually one is only interested in a few column
1754 values of the object, this is not very helpful.
1756 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1757 it. Simply define a hook that L<Data::Dumper> will call on the object before
1758 dumping it. For example,
1765 result_source => undef,
1773 local $Data::Dumper::Freezer = '_dumper_hook';
1775 my $cd = $schema->resultset('CD')->find(1);
1777 # dumps $cd without its ResultSource
1779 If the structure of your schema is such that there is a common base class for
1780 all your table classes, simply put a method similar to C<_dumper_hook> in the
1781 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1782 will automagically clean up your data before printing it. See
1783 L<Data::Dumper/EXAMPLES> for more information.
1787 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1788 executed as well as notifications of query completion and transaction
1789 begin/commit. If you'd like to profile the SQL you can subclass the
1790 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1793 package My::Profiler;
1796 use base 'DBIx::Class::Storage::Statistics';
1798 use Time::HiRes qw(time);
1807 $self->print("Executing $sql: ".join(', ', @params)."\n");
1816 my $elapsed = sprintf("%0.4f", time() - $start);
1817 $self->print("Execution took $elapsed seconds.\n");
1823 You can then install that class as the debugging object:
1825 __PACKAGE__->storage->debugobj(new My::Profiler());
1826 __PACKAGE__->storage->debug(1);
1828 A more complicated example might involve storing each execution of SQL in an
1836 my $elapsed = time() - $start;
1837 push(@{ $calls{$sql} }, {
1843 You could then create average, high and low execution times for an SQL
1844 statement and dig down to see if certain parameters cause aberrant behavior.
1845 You might want to check out L<DBIx::Class::QueryLog> as well.
1847 =head1 STARTUP SPEED
1849 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1850 as the ORM loads all the relevant classes. This section examines
1851 techniques for reducing the startup delay.
1853 These tips are are listed in order of decreasing effectiveness - so the
1854 first tip, if applicable, should have the greatest effect on your
1857 =head2 Statically Define Your Schema
1860 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1861 classes dynamically based on the database schema then there will be a
1862 significant startup delay.
1864 For production use a statically defined schema (which can be generated
1865 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1866 the database schema once - see
1867 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1868 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1869 details on creating static schemas from a database).
1871 =head2 Move Common Startup into a Base Class
1873 Typically L<DBIx::Class> result classes start off with
1875 use base qw/DBIx::Class/;
1876 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1878 If this preamble is moved into a common base class:-
1882 use base qw/DBIx::Class/;
1883 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1886 and each result class then uses this as a base:-
1888 use base qw/MyDBICbase/;
1890 then the load_components is only performed once, which can result in a
1891 considerable startup speedup for schemas with many classes.
1893 =head2 Explicitly List Schema Result Classes
1895 The schema class will normally contain
1897 __PACKAGE__->load_classes();
1899 to load the result classes. This will use L<Module::Find|Module::Find>
1900 to find and load the appropriate modules. Explicitly defining the
1901 classes you wish to load will remove the overhead of
1902 L<Module::Find|Module::Find> and the related directory operations:-
1904 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1906 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1907 syntax to load the appropriate classes there is not a direct alternative
1908 avoiding L<Module::Find|Module::Find>.
1912 =head2 Cached statements
1914 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1915 This is normally a good idea, but if too many statements are cached, the database may use too much
1916 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1917 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1919 # print all currently cached prepared statements
1920 print for keys %{$schema->storage->dbh->{CachedKids}};
1921 # get a count of currently cached prepared statements
1922 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1924 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1927 my $kids = $schema->storage->dbh->{CachedKids};
1928 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1930 But what you probably want is to expire unused statements and not those that are used frequently.
1931 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1935 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1936 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },