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 return $rs->page(2); # records for page 2
24 You can get a L<Data::Page> object for the resultset (suitable for use
25 in e.g. a template) using the C<pager> method:
29 =head2 Complex WHERE clauses
31 Sometimes you need to formulate a query using specific operators:
33 my @albums = $schema->resultset('Album')->search({
34 artist => { 'like', '%Lamb%' },
35 title => { 'like', '%Fear of Fours%' },
38 This results in something like the following C<WHERE> clause:
40 WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
42 Other queries might require slightly more complex logic:
44 my @albums = $schema->resultset('Album')->search({
47 artist => { 'like', '%Smashing Pumpkins%' },
48 title => 'Siamese Dream',
50 artist => 'Starchildren',
54 This results in the following C<WHERE> clause:
56 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
57 OR artist = 'Starchildren'
59 For more information on generating complex queries, see
60 L<SQL::Abstract/WHERE CLAUSES>.
62 =head2 Retrieve one and only one row from a resultset
64 Sometimes you need only the first "top" row of a resultset. While this
65 can be easily done with L<< $rs->first|DBIx::Class::ResultSet/first
66 >>, it is suboptimal, as a full blown cursor for the resultset will be
67 created and then immediately destroyed after fetching the first row
68 object. L<< $rs->single|DBIx::Class::ResultSet/single >> is designed
69 specifically for this case - it will grab the first returned result
70 without even instantiating a cursor.
72 Before replacing all your calls to C<first()> with C<single()> please observe the
79 While single() takes a search condition just like search() does, it does
80 _not_ accept search attributes. However one can always chain a single() to
83 my $top_cd = $cd_rs->search({}, { order_by => 'rating' })->single;
88 Since single() is the engine behind find(), it is designed to fetch a
89 single row per database query. Thus a warning will be issued when the
90 underlying SELECT returns more than one row. Sometimes however this usage
91 is valid: i.e. we have an arbitrary number of cd's but only one of them is
92 at the top of the charts at any given time. If you know what you are doing,
93 you can silence the warning by explicitly limiting the resultset size:
95 my $top_cd = $cd_rs->search ({}, { order_by => 'rating', rows => 1 })->single;
99 =head2 Arbitrary SQL through a custom ResultSource
101 Sometimes you have to run arbitrary SQL because your query is too complex
102 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
103 be optimized for your database in a special way, but you still want to
104 get the results as a L<DBIx::Class::ResultSet>.
106 The recommended way to accomplish this is by defining a separate
107 L<ResultSource::View|DBIx::Class::ResultSource::View> for your query.
109 package My::Schema::Result::UserFriendsComplex;
112 use base qw/DBIx::Class/;
114 use DBIx::Class::ResultSource::View;
116 __PACKAGE__->load_components('Core');
117 __PACKAGE__->table_class('DBIx::Class::ResultSource::View');
119 # ->table, ->add_columns, etc.
121 __PACKAGE__->result_source_instance->is_virtual(1);
122 __PACKAGE__->result_source_instance->view_definition(q[
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
132 Next, you can execute your complex query using bind parameters like this:
134 my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
136 bind => [ 12345, 12345 ]
140 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
141 that you cannot modify the rows it contains, ie. cannot call L</update>,
142 L</delete>, ... on it).
144 Note that you cannot have bind parameters unless is_virtual is set to true.
146 =head2 Using specific columns
148 When you only want specific columns from a table, you can use
149 C<columns> to specify which ones you need. This is useful to avoid
150 loading columns with large amounts of data that you aren't about to
153 my $rs = $schema->resultset('Artist')->search(
156 columns => [qw/ name /]
161 # SELECT artist.name FROM artist
163 This is a shortcut for C<select> and C<as>, see below. C<columns>
164 cannot be used together with C<select> and C<as>.
166 =head2 Using database functions or stored procedures
168 The combination of C<select> and C<as> can be used to return the result of a
169 database function or stored procedure as a column value. You use C<select> to
170 specify the source for your column value (e.g. a column name, function, or
171 stored procedure name). You then use C<as> to set the column name you will use
172 to access the returned value:
174 my $rs = $schema->resultset('Artist')->search(
177 select => [ 'name', { LENGTH => 'name' } ],
178 as => [qw/ name name_length /],
183 # SELECT name name, LENGTH( name )
186 Note that the C< as > attribute has absolutely nothing to with the sql
187 syntax C< SELECT foo AS bar > (see the documentation in
188 L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
189 column in your base class (i.e. it was added with C<add_columns>), you
190 just access it as normal. Our C<Artist> class has a C<name> column, so
191 we just use the C<name> accessor:
193 my $artist = $rs->first();
194 my $name = $artist->name();
196 If on the other hand the alias does not correspond to an existing column, you
197 have to fetch the value using the C<get_column> accessor:
199 my $name_length = $artist->get_column('name_length');
201 If you don't like using C<get_column>, you can always create an accessor for
202 any of your aliases using either of these:
204 # Define accessor manually:
205 sub name_length { shift->get_column('name_length'); }
207 # Or use DBIx::Class::AccessorGroup:
208 __PACKAGE__->mk_group_accessors('column' => 'name_length');
210 =head2 SELECT DISTINCT with multiple columns
212 my $rs = $schema->resultset('Artist')->search(
215 columns => [ qw/artist_id name rank/ ],
220 my $rs = $schema->resultset('Artist')->search(
223 columns => [ qw/artist_id name rank/ ],
224 group_by => [ qw/artist_id name rank/ ],
229 # SELECT me.artist_id, me.name, me.rank
231 # GROUP BY artist_id, name, rank
233 =head2 SELECT COUNT(DISTINCT colname)
235 my $rs = $schema->resultset('Artist')->search(
238 columns => [ qw/name/ ],
243 my $rs = $schema->resultset('Artist')->search(
246 columns => [ qw/name/ ],
247 group_by => [ qw/name/ ],
251 my $count = $rs->count;
254 # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) count_subq:
256 =head2 Grouping results
258 L<DBIx::Class> supports C<GROUP BY> as follows:
260 my $rs = $schema->resultset('Artist')->search(
264 select => [ 'name', { count => 'cds.id' } ],
265 as => [qw/ name cd_count /],
266 group_by => [qw/ name /]
271 # SELECT name, COUNT( cd.id ) FROM artist
272 # LEFT JOIN cd ON artist.id = cd.artist
275 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
276 are in any way unsure about the use of the attributes above (C< join
277 >, C< select >, C< as > and C< group_by >).
279 =head2 Subqueries (EXPERIMENTAL)
281 You can write subqueries relatively easily in DBIC.
283 my $inside_rs = $schema->resultset('Artist')->search({
284 name => [ 'Billy Joel', 'Brittany Spears' ],
287 my $rs = $schema->resultset('CD')->search({
288 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
291 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
293 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
294 The following will B<not> work:
296 my $rs = $schema->resultset('CD')->search({
297 artist_id => $inside_rs->get_column('id')->as_query,
302 Subqueries are supported in the where clause (first hashref), and in the
303 from, select, and +select attributes.
305 =head3 Correlated subqueries
307 my $cdrs = $schema->resultset('CD');
308 my $rs = $cdrs->search({
310 '=' => $cdrs->search(
311 { artist_id => { '=' => \'me.artist_id' } },
313 )->get_column('year')->max_rs->as_query,
317 That creates the following SQL:
319 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
322 SELECT MAX(inner.year)
324 WHERE artist_id = me.artist_id
329 Please note that subqueries are considered an experimental feature.
331 =head2 Predefined searches
333 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
334 and defining often used searches as methods:
336 package My::DBIC::ResultSet::CD;
339 use base 'DBIx::Class::ResultSet';
341 sub search_cds_ordered {
344 return $self->search(
346 { order_by => 'name DESC' },
352 To use your resultset, first tell DBIx::Class to create an instance of it
353 for you, in your My::DBIC::Schema::CD class:
355 # class definition as normal
356 __PACKAGE__->load_components(qw/ Core /);
357 __PACKAGE__->table('cd');
359 # tell DBIC to use the custom ResultSet class
360 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
362 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
364 Then call your new method in your code:
366 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
368 =head2 Using SQL functions on the left hand side of a comparison
370 Using SQL functions on the left hand side of a comparison is generally
371 not a good idea since it requires a scan of the entire table. However,
372 it can be accomplished with C<DBIx::Class> when necessary.
374 If you do not have quoting on, simply include the function in your search
375 specification as you would any column:
377 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
379 With quoting on, or for a more portable solution, use the C<where>
382 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
386 (When the bind args ordering bug is fixed, this technique will be better
387 and can replace the one above.)
389 With quoting on, or for a more portable solution, use the C<where> and
393 where => \'YEAR(date_of_birth) = ?',
399 =head1 JOINS AND PREFETCHING
401 =head2 Using joins and prefetch
403 You can use the C<join> attribute to allow searching on, or sorting your
404 results by, one or more columns in a related table.
406 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
408 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
410 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
412 my $rs = $schema->resultset('CD')->search(
414 'artists.name' => 'Bob Marley'
417 join => 'artists', # join the artist table
422 # SELECT cd.* FROM cd
423 # JOIN artist ON cd.artist = artist.id
424 # WHERE artist.name = 'Bob Marley'
426 In that example both the join, and the condition use the relationship name rather than the table name
427 (see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
429 If required, you can now sort on any column in the related tables by including
430 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
432 my $rs = $schema->resultset('CD')->search(
434 'artists.name' => 'Bob Marley'
438 order_by => [qw/ artists.name /]
443 # SELECT cd.* FROM cd
444 # JOIN artist ON cd.artist = artist.id
445 # WHERE artist.name = 'Bob Marley'
446 # ORDER BY artist.name
448 Note that the C<join> attribute should only be used when you need to search or
449 sort using columns in a related table. Joining related tables when you only
450 need columns from the main table will make performance worse!
452 Now let's say you want to display a list of CDs, each with the name of the
453 artist. The following will work fine:
455 while (my $cd = $rs->next) {
456 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
459 There is a problem however. We have searched both the C<cd> and C<artist> tables
460 in our main query, but we have only returned data from the C<cd> table. To get
461 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
464 SELECT artist.* FROM artist WHERE artist.id = ?
466 A statement like the one above will run for each and every CD returned by our
467 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
470 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
471 This allows you to fetch results from related tables in advance:
473 my $rs = $schema->resultset('CD')->search(
475 'artists.name' => 'Bob Marley'
479 order_by => [qw/ artists.name /],
480 prefetch => 'artists' # return artist data too!
484 # Equivalent SQL (note SELECT from both "cd" and "artist"):
485 # SELECT cd.*, artist.* FROM cd
486 # JOIN artist ON cd.artist = artist.id
487 # WHERE artist.name = 'Bob Marley'
488 # ORDER BY artist.name
490 The code to print the CD list remains the same:
492 while (my $cd = $rs->next) {
493 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
496 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
497 so no additional SQL statements are executed. You now have a much more
500 Also note that C<prefetch> should only be used when you know you will
501 definitely use data from a related table. Pre-fetching related tables when you
502 only need columns from the main table will make performance worse!
504 =head2 Multiple joins
506 In the examples above, the C<join> attribute was a scalar. If you
507 pass an array reference instead, you can join to multiple tables. In
508 this example, we want to limit the search further, using
511 # Relationships defined elsewhere:
512 # CD->belongs_to('artist' => 'Artist');
513 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
514 my $rs = $schema->resultset('CD')->search(
516 'artist.name' => 'Bob Marley'
517 'liner_notes.notes' => { 'like', '%some text%' },
520 join => [qw/ artist liner_notes /],
521 order_by => [qw/ artist.name /],
526 # SELECT cd.*, artist.*, liner_notes.* FROM cd
527 # JOIN artist ON cd.artist = artist.id
528 # JOIN liner_notes ON cd.id = liner_notes.cd
529 # WHERE artist.name = 'Bob Marley'
530 # ORDER BY artist.name
532 =head2 Multi-step joins
534 Sometimes you want to join more than one relationship deep. In this example,
535 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
536 contain a specific string:
538 # Relationships defined elsewhere:
539 # Artist->has_many('cds' => 'CD', 'artist');
540 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
542 my $rs = $schema->resultset('Artist')->search(
544 'liner_notes.notes' => { 'like', '%some text%' },
548 'cds' => 'liner_notes'
554 # SELECT artist.* FROM artist
555 # LEFT JOIN cd ON artist.id = cd.artist
556 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
557 # WHERE liner_notes.notes LIKE '%some text%'
559 Joins can be nested to an arbitrary level. So if we decide later that we
560 want to reduce the number of Artists returned based on who wrote the liner
563 # Relationship defined elsewhere:
564 # LinerNotes->belongs_to('author' => 'Person');
566 my $rs = $schema->resultset('Artist')->search(
568 'liner_notes.notes' => { 'like', '%some text%' },
569 'author.name' => 'A. Writer'
574 'liner_notes' => 'author'
581 # SELECT artist.* FROM artist
582 # LEFT JOIN cd ON artist.id = cd.artist
583 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
584 # LEFT JOIN author ON author.id = liner_notes.author
585 # WHERE liner_notes.notes LIKE '%some text%'
586 # AND author.name = 'A. Writer'
588 =head2 Multi-step and multiple joins
590 With various combinations of array and hash references, you can join
591 tables in any combination you desire. For example, to join Artist to
592 CD and Concert, and join CD to LinerNotes:
594 # Relationships defined elsewhere:
595 # Artist->has_many('concerts' => 'Concert', 'artist');
597 my $rs = $schema->resultset('Artist')->search(
610 # SELECT artist.* FROM artist
611 # LEFT JOIN cd ON artist.id = cd.artist
612 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
613 # LEFT JOIN concert ON artist.id = concert.artist
615 =head2 Multi-step prefetch
617 C<prefetch> can be nested more than one relationship
618 deep using the same syntax as a multi-step join:
620 my $rs = $schema->resultset('Tag')->search(
630 # SELECT tag.*, cd.*, artist.* FROM tag
631 # JOIN cd ON tag.cd = cd.id
632 # JOIN artist ON cd.artist = artist.id
634 Now accessing our C<cd> and C<artist> relationships does not need additional
637 my $tag = $rs->first;
638 print $tag->cd->artist->name;
640 =head1 ROW-LEVEL OPERATIONS
642 =head2 Retrieving a row object's Schema
644 It is possible to get a Schema object from a row object like so:
646 my $schema = $cd->result_source->schema;
647 # use the schema as normal:
648 my $artist_rs = $schema->resultset('Artist');
650 This can be useful when you don't want to pass around a Schema object to every
653 =head2 Getting the value of the primary key for the last database insert
655 AKA getting last_insert_id
657 Thanks to the core component PK::Auto, this is straightforward:
659 my $foo = $rs->create(\%blah);
661 my $id = $foo->id; # foo->my_primary_key_field will also work.
663 If you are not using autoincrementing primary keys, this will probably
664 not work, but then you already know the value of the last primary key anyway.
666 =head2 Stringification
668 Employ the standard stringification technique by using the L<overload>
671 To make an object stringify itself as a single column, use something
672 like this (replace C<name> with the column/method of your choice):
674 use overload '""' => sub { shift->name}, fallback => 1;
676 For more complex stringification, you can use an anonymous subroutine:
678 use overload '""' => sub { $_[0]->name . ", " .
679 $_[0]->address }, fallback => 1;
681 =head3 Stringification Example
683 Suppose we have two tables: C<Product> and C<Category>. The table
686 Product(id, Description, category)
687 Category(id, Description)
689 C<category> is a foreign key into the Category table.
691 If you have a Product object C<$obj> and write something like
695 things will not work as expected.
697 To obtain, for example, the category description, you should add this
698 method to the class defining the Category table:
700 use overload "" => sub {
703 return $self->Description;
706 =head2 Want to know if find_or_create found or created a row?
708 Just use C<find_or_new> instead, then check C<in_storage>:
710 my $obj = $rs->find_or_new({ blah => 'blarg' });
711 unless ($obj->in_storage) {
713 # do whatever else you wanted if it was a new row
716 =head2 Static sub-classing DBIx::Class result classes
718 AKA adding additional relationships/methods/etc. to a model for a
719 specific usage of the (shared) model.
723 package My::App::Schema;
725 use base DBIx::Class::Schema;
727 # load subclassed classes from My::App::Schema::Result/ResultSet
728 __PACKAGE__->load_namespaces;
730 # load classes from shared model
732 'My::Shared::Model::Result' => [qw/
739 B<Result-Subclass definition>
741 package My::App::Schema::Result::Baz;
745 use base My::Shared::Model::Result::Baz;
747 # WARNING: Make sure you call table() again in your subclass,
748 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
749 # and the class name is not correctly registered as a source
750 __PACKAGE__->table('baz');
752 sub additional_method {
753 return "I'm an additional method only needed by this app";
758 =head2 Dynamic Sub-classing DBIx::Class proxy classes
760 AKA multi-class object inflation from one table
762 L<DBIx::Class> classes are proxy classes, therefore some different
763 techniques need to be employed for more than basic subclassing. In
764 this example we have a single user table that carries a boolean bit
765 for admin. We would like like to give the admin users
766 objects (L<DBIx::Class::Row>) the same methods as a regular user but
767 also special admin only methods. It doesn't make sense to create two
768 seperate proxy-class files for this. We would be copying all the user
769 methods into the Admin class. There is a cleaner way to accomplish
772 Overriding the C<inflate_result> method within the User proxy-class
773 gives us the effect we want. This method is called by
774 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
775 grab the object being returned, inspect the values we are looking for,
776 bless it if it's an admin object, and then return it. See the example
783 use base qw/DBIx::Class::Schema/;
785 __PACKAGE__->load_namespaces;
790 B<Proxy-Class definitions>
792 package My::Schema::Result::User;
796 use base qw/DBIx::Class/;
798 ### Define what our admin class is, for ensure_class_loaded()
799 my $admin_class = __PACKAGE__ . '::Admin';
801 __PACKAGE__->load_components(qw/Core/);
803 __PACKAGE__->table('users');
805 __PACKAGE__->add_columns(qw/user_id email password
806 firstname lastname active
809 __PACKAGE__->set_primary_key('user_id');
813 my $ret = $self->next::method(@_);
814 if( $ret->admin ) {### If this is an admin, rebless for extra functions
815 $self->ensure_class_loaded( $admin_class );
816 bless $ret, $admin_class;
822 print "I am a regular user.\n";
829 package My::Schema::Result::User::Admin;
833 use base qw/My::Schema::Result::User/;
835 # This line is important
836 __PACKAGE__->table('users');
840 print "I am an admin.\n";
846 print "I am doing admin stuff\n";
858 my $user_data = { email => 'someguy@place.com',
862 my $admin_data = { email => 'someadmin@adminplace.com',
866 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
868 $schema->resultset('User')->create( $user_data );
869 $schema->resultset('User')->create( $admin_data );
871 ### Now we search for them
872 my $user = $schema->resultset('User')->single( $user_data );
873 my $admin = $schema->resultset('User')->single( $admin_data );
875 print ref $user, "\n";
876 print ref $admin, "\n";
878 print $user->password , "\n"; # pass1
879 print $admin->password , "\n";# pass2; inherited from User
880 print $user->hello , "\n";# I am a regular user.
881 print $admin->hello, "\n";# I am an admin.
883 ### The statement below will NOT print
884 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
885 ### The statement below will print
886 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
888 =head2 Skip row object creation for faster results
890 DBIx::Class is not built for speed, it's built for convenience and
891 ease of use, but sometimes you just need to get the data, and skip the
894 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
896 my $rs = $schema->resultset('CD');
898 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
900 my $hash_ref = $rs->find(1);
904 Beware, changing the Result class using
905 L<DBIx::Class::ResultSet/result_class> will replace any existing class
906 completely including any special components loaded using
907 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
909 =head2 Get raw data for blindingly fast results
911 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
912 above is not fast enough for you, you can use a DBIx::Class to return values
913 exactly as they come out of the database with none of the convenience methods
916 This is used like so:
918 my $cursor = $rs->cursor
919 while (my @vals = $cursor->next) {
920 # use $val[0..n] here
923 You will need to map the array offsets to particular columns (you can
924 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
926 =head1 RESULTSET OPERATIONS
928 =head2 Getting Schema from a ResultSet
930 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
932 $rs->result_source->schema
934 =head2 Getting Columns Of Data
938 If you want to find the sum of a particular column there are several
939 ways, the obvious one is to use search:
941 my $rs = $schema->resultset('Items')->search(
944 select => [ { sum => 'Cost' } ],
945 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
948 my $tc = $rs->first->get_column('total_cost');
950 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
951 returned when you ask the C<ResultSet> for a column using
954 my $cost = $schema->resultset('Items')->get_column('Cost');
957 With this you can also do:
959 my $minvalue = $cost->min;
960 my $maxvalue = $cost->max;
962 Or just iterate through the values of this column only:
964 while ( my $c = $cost->next ) {
968 foreach my $c ($cost->all) {
972 C<ResultSetColumn> only has a limited number of built-in functions. If
973 you need one that it doesn't have, then you can use the C<func> method
976 my $avg = $cost->func('AVERAGE');
978 This will cause the following SQL statement to be run:
980 SELECT AVERAGE(Cost) FROM Items me
982 Which will of course only work if your database supports this function.
983 See L<DBIx::Class::ResultSetColumn> for more documentation.
985 =head2 Creating a result set from a set of rows
987 Sometimes you have a (set of) row objects that you want to put into a
988 resultset without the need to hit the DB again. You can do that by using the
989 L<set_cache|DBIx::Class::Resultset/set_cache> method:
991 my @uploadable_groups;
992 while (my $group = $groups->next) {
993 if ($group->can_upload($self)) {
994 push @uploadable_groups, $group;
997 my $new_rs = $self->result_source->resultset;
998 $new_rs->set_cache(\@uploadable_groups);
1002 =head1 USING RELATIONSHIPS
1004 =head2 Create a new row in a related table
1006 my $author = $book->create_related('author', { name => 'Fred'});
1008 =head2 Search in a related table
1010 Only searches for books named 'Titanic' by the author in $author.
1012 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1014 =head2 Delete data in a related table
1016 Deletes only the book named Titanic by the author in $author.
1018 $author->delete_related('books', { name => 'Titanic' });
1020 =head2 Ordering a relationship result set
1022 If you always want a relation to be ordered, you can specify this when you
1023 create the relationship.
1025 To order C<< $book->pages >> by descending page_number, create the relation
1028 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
1030 =head2 Filtering a relationship result set
1032 If you want to get a filtered result set, you can just add add to $attr as follows:
1034 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1036 =head2 Many-to-many relationships
1038 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1041 use base 'DBIx::Class';
1042 __PACKAGE__->load_components('Core');
1043 __PACKAGE__->table('user');
1044 __PACKAGE__->add_columns(qw/id name/);
1045 __PACKAGE__->set_primary_key('id');
1046 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1047 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1049 package My::UserAddress;
1050 use base 'DBIx::Class';
1051 __PACKAGE__->load_components('Core');
1052 __PACKAGE__->table('user_address');
1053 __PACKAGE__->add_columns(qw/user address/);
1054 __PACKAGE__->set_primary_key(qw/user address/);
1055 __PACKAGE__->belongs_to('user' => 'My::User');
1056 __PACKAGE__->belongs_to('address' => 'My::Address');
1058 package My::Address;
1059 use base 'DBIx::Class';
1060 __PACKAGE__->load_components('Core');
1061 __PACKAGE__->table('address');
1062 __PACKAGE__->add_columns(qw/id street town area_code country/);
1063 __PACKAGE__->set_primary_key('id');
1064 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1065 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1067 $rs = $user->addresses(); # get all addresses for a user
1068 $rs = $address->users(); # get all users for an address
1070 =head2 Relationships across DB schemas
1072 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1073 is easy as long as the schemas themselves are all accessible via the same DBI
1074 connection. In most cases, this means that they are on the same database host
1075 as each other and your connecting database user has the proper permissions to them.
1077 To accomplish this one only needs to specify the DB schema name in the table
1078 declaration, like so...
1080 package MyDatabase::Main::Artist;
1081 use base qw/DBIx::Class/;
1082 __PACKAGE__->load_components(qw/PK::Auto Core/);
1084 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1086 __PACKAGE__->add_columns(qw/ artist_id name /);
1087 __PACKAGE__->set_primary_key('artist_id');
1088 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1092 Whatever string you specify there will be used to build the "FROM" clause in SQL
1095 The big drawback to this is you now have DB schema names hardcoded in your
1096 class files. This becomes especially troublesome if you have multiple instances
1097 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1098 the DB schemas are named based on the environment (e.g. database1_dev).
1100 However, one can dynamically "map" to the proper DB schema by overriding the
1101 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1102 building a renaming facility, like so:
1104 package MyDatabase::Schema;
1107 extends 'DBIx::Class::Schema';
1109 around connection => sub {
1110 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1112 my $postfix = delete $attr->{schema_name_postfix};
1117 $self->append_db_name($postfix);
1121 sub append_db_name {
1122 my ( $self, $postfix ) = @_;
1126 { $_->name =~ /^\w+\./mx }
1128 { $self->source($_) }
1131 foreach my $source (@sources_with_db) {
1132 my $name = $source->name;
1133 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1135 $source->name($name);
1141 By overridding the L<connection|DBIx::Class::Schama/connection>
1142 method and extracting a custom option from the provided \%attr hashref one can
1143 then simply iterate over all the Schema's ResultSources, renaming them as
1146 To use this facility, simply add or modify the \%attr hashref that is passed to
1147 L<connection|DBIx::Class::Schama/connect>, as follows:
1150 = MyDatabase::Schema->connect(
1155 schema_name_postfix => '_dev'
1156 # ... Other options as desired ...
1159 Obviously, one could accomplish even more advanced mapping via a hash map or a
1164 As of version 0.04001, there is improved transaction support in
1165 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1166 example of the recommended way to use it:
1168 my $genus = $schema->resultset('Genus')->find(12);
1170 my $coderef2 = sub {
1175 my $coderef1 = sub {
1176 $genus->add_to_species({ name => 'troglodyte' });
1179 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1180 return $genus->species;
1185 $rs = $schema->txn_do($coderef1);
1188 if ($@) { # Transaction failed
1189 die "the sky is falling!" #
1190 if ($@ =~ /Rollback failed/); # Rollback failed
1192 deal_with_failed_transaction();
1195 Nested transactions will work as expected. That is, only the outermost
1196 transaction will actually issue a commit to the $dbh, and a rollback
1197 at any level of any transaction will cause the entire nested
1198 transaction to fail. Support for savepoints and for true nested
1199 transactions (for databases that support them) will hopefully be added
1204 =head2 Creating Schemas From An Existing Database
1206 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1207 L<DBIx::Class::Schema> and associated sources by examining the database.
1209 The recommend way of achieving this is to use the
1210 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1212 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1213 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1215 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1216 source definitions for all the tables found in the C<foo> database.
1218 =head2 Creating DDL SQL
1220 The following functionality requires you to have L<SQL::Translator>
1221 (also known as "SQL Fairy") installed.
1223 To create a set of database-specific .sql files for the above schema:
1225 my $schema = My::Schema->connect($dsn);
1226 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1231 By default this will create schema files in the current directory, for
1232 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1234 To create a new database using the schema:
1236 my $schema = My::Schema->connect($dsn);
1237 $schema->deploy({ add_drop_tables => 1});
1239 To import created .sql files using the mysql client:
1241 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1243 To create C<ALTER TABLE> conversion scripts to update a database to a
1244 newer version of your schema at a later point, first set a new
1245 C<$VERSION> in your Schema file, then:
1247 my $schema = My::Schema->connect($dsn);
1248 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1254 This will produce new database-specific .sql files for the new version
1255 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1256 requires that the files for 0.1 as created above are available in the
1257 given directory to diff against.
1259 =head2 Select from dual
1261 Dummy tables are needed by some databases to allow calling functions
1262 or expressions that aren't based on table content, for examples of how
1263 this applies to various database types, see:
1264 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1266 Note: If you're using Oracles dual table don't B<ever> do anything
1267 other than a select, if you CRUD on your dual table you *will* break
1270 Make a table class as you would for any other table
1272 package MyAppDB::Dual;
1275 use base 'DBIx::Class';
1276 __PACKAGE__->load_components("Core");
1277 __PACKAGE__->table("Dual");
1278 __PACKAGE__->add_columns(
1280 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1283 Once you've loaded your table class select from it using C<select>
1284 and C<as> instead of C<columns>
1286 my $rs = $schema->resultset('Dual')->search(undef,
1287 { select => [ 'sydate' ],
1292 All you have to do now is be careful how you access your resultset, the below
1293 will not work because there is no column called 'now' in the Dual table class
1295 while (my $dual = $rs->next) {
1296 print $dual->now."\n";
1298 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1300 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1301 your Dual class for whatever you wanted to select from dual, but that's just
1302 silly, instead use C<get_column>
1304 while (my $dual = $rs->next) {
1305 print $dual->get_column('now')."\n";
1310 my $cursor = $rs->cursor;
1311 while (my @vals = $cursor->next) {
1312 print $vals[0]."\n";
1315 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1316 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1317 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1318 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1319 L<SQL::Translator> to not create table dual:
1322 add_drop_table => 1,
1323 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1325 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1327 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1329 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1330 while ( my $dual = $rs->next ) {
1331 print $dual->{now}."\n";
1334 Here are some example C<select> conditions to illustrate the different syntax
1335 you could use for doing stuff like
1336 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1338 # get a sequence value
1339 select => [ 'A_SEQ.nextval' ],
1341 # get create table sql
1342 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1344 # get a random num between 0 and 100
1345 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1348 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1351 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1353 # which day of the week were you born on?
1354 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1356 # select 16 rows from dual
1357 select => [ "'hello'" ],
1359 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1363 =head2 Adding Indexes And Functions To Your SQL
1365 Often you will want indexes on columns on your table to speed up searching. To
1366 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1367 class (refer to the advanced
1368 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1369 to share a hook between multiple sources):
1371 package My::Schema::Result::Artist;
1373 __PACKAGE__->table('artist');
1374 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1376 sub sqlt_deploy_hook {
1377 my ($self, $sqlt_table) = @_;
1379 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1384 Sometimes you might want to change the index depending on the type of the
1385 database for which SQL is being generated:
1387 my ($db_type = $sqlt_table->schema->translator->producer_type)
1388 =~ s/^SQL::Translator::Producer:://;
1390 You can also add hooks to the schema level to stop certain tables being
1397 sub sqlt_deploy_hook {
1398 my ($self, $sqlt_schema) = @_;
1400 $sqlt_schema->drop_table('table_name');
1403 You could also add views, procedures or triggers to the output using
1404 L<SQL::Translator::Schema/add_view>,
1405 L<SQL::Translator::Schema/add_procedure> or
1406 L<SQL::Translator::Schema/add_trigger>.
1409 =head2 Schema versioning
1411 The following example shows simplistically how you might use DBIx::Class to
1412 deploy versioned schemas to your customers. The basic process is as follows:
1418 Create a DBIx::Class schema
1430 Modify schema to change functionality
1434 Deploy update to customers
1438 B<Create a DBIx::Class schema>
1440 This can either be done manually, or generated from an existing database as
1441 described under L</Creating Schemas From An Existing Database>
1445 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1447 B<Deploy to customers>
1449 There are several ways you could deploy your schema. These are probably
1450 beyond the scope of this recipe, but might include:
1456 Require customer to apply manually using their RDBMS.
1460 Package along with your app, making database dump/schema update/tests
1461 all part of your install.
1465 B<Modify the schema to change functionality>
1467 As your application evolves, it may be necessary to modify your schema
1468 to change functionality. Once the changes are made to your schema in
1469 DBIx::Class, export the modified schema and the conversion scripts as
1470 in L</Creating DDL SQL>.
1472 B<Deploy update to customers>
1474 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1475 Schema class. This will add a new table to your database called
1476 C<dbix_class_schema_vesion> which will keep track of which version is installed
1477 and warn if the user trys to run a newer schema version than the
1478 database thinks it has.
1480 Alternatively, you can send the conversion sql scripts to your
1483 =head2 Setting quoting for the generated SQL.
1485 If the database contains column names with spaces and/or reserved words, they
1486 need to be quoted in the SQL queries. This is done using:
1488 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1489 __PACKAGE__->storage->sql_maker->name_sep('.');
1491 The first sets the quote characters. Either a pair of matching
1492 brackets, or a C<"> or C<'>:
1494 __PACKAGE__->storage->sql_maker->quote_char('"');
1496 Check the documentation of your database for the correct quote
1497 characters to use. C<name_sep> needs to be set to allow the SQL
1498 generator to put the quotes the correct place.
1500 In most cases you should set these as part of the arguments passed to
1501 L<DBIx::Class::Schema/connect>:
1503 my $schema = My::Schema->connect(
1513 =head2 Setting limit dialect for SQL::Abstract::Limit
1515 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1516 the remote SQL server by looking at the database handle. This is a
1517 common problem when using the DBD::JDBC, since the DBD-driver only
1518 know that in has a Java-driver available, not which JDBC driver the
1519 Java component has loaded. This specifically sets the limit_dialect
1520 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1523 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1525 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1526 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1528 The limit dialect can also be set at connect time by specifying a
1529 C<limit_dialect> key in the final hash as shown above.
1531 =head2 Working with PostgreSQL array types
1533 You can also assign values to PostgreSQL array columns by passing array
1534 references in the C<\%columns> (C<\%vals>) hashref of the
1535 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1538 $resultset->create({
1539 numbers => [1, 2, 3]
1544 numbers => [1, 2, 3]
1551 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1552 methods) you cannot directly use array references (since this is interpreted as
1553 a list of values to be C<OR>ed), but you can use the following syntax to force
1554 passing them as bind values:
1558 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1562 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1563 placeholders and bind values (subqueries)> for more explanation. Note that
1564 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1565 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1566 arrayrefs together with the column name, like this: C<< [column_name => value]
1569 =head1 BOOTSTRAPPING/MIGRATING
1571 =head2 Easy migration from class-based to schema-based setup
1573 You want to start using the schema-based approach to L<DBIx::Class>
1574 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1575 of existing classes that you don't want to move by hand. Try this nifty script
1579 use SQL::Translator;
1581 my $schema = MyDB->schema_instance;
1583 my $translator = SQL::Translator->new(
1584 debug => $debug || 0,
1585 trace => $trace || 0,
1586 no_comments => $no_comments || 0,
1587 show_warnings => $show_warnings || 0,
1588 add_drop_table => $add_drop_table || 0,
1589 validate => $validate || 0,
1591 'DBIx::Schema' => $schema,
1594 'prefix' => 'My::Schema',
1598 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1599 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1601 my $output = $translator->translate(@args) or die
1602 "Error: " . $translator->error;
1606 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1607 namespace, which is currently left as an exercise for the reader.
1609 =head1 OVERLOADING METHODS
1611 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1612 method calls, useful for things like default values and triggers. You have to
1613 use calls to C<next::method> to overload methods. More information on using
1614 L<Class::C3> with L<DBIx::Class> can be found in
1615 L<DBIx::Class::Manual::Component>.
1617 =head2 Setting default values for a row
1619 It's as simple as overriding the C<new> method. Note the use of
1623 my ( $class, $attrs ) = @_;
1625 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1627 my $new = $class->next::method($attrs);
1632 For more information about C<next::method>, look in the L<Class::C3>
1633 documentation. See also L<DBIx::Class::Manual::Component> for more
1634 ways to write your own base classes to do this.
1636 People looking for ways to do "triggers" with DBIx::Class are probably
1637 just looking for this.
1639 =head2 Changing one field whenever another changes
1641 For example, say that you have three columns, C<id>, C<number>, and
1642 C<squared>. You would like to make changes to C<number> and have
1643 C<squared> be automagically set to the value of C<number> squared.
1644 You can accomplish this by overriding C<store_column>:
1647 my ( $self, $name, $value ) = @_;
1648 if ($name eq 'number') {
1649 $self->squared($value * $value);
1651 $self->next::method($name, $value);
1654 Note that the hard work is done by the call to C<next::method>, which
1655 redispatches your call to store_column in the superclass(es).
1657 =head2 Automatically creating related objects
1659 You might have a class C<Artist> which has many C<CD>s. Further, you
1660 want to create a C<CD> object every time you insert an C<Artist> object.
1661 You can accomplish this by overriding C<insert> on your objects:
1664 my ( $self, @args ) = @_;
1665 $self->next::method(@args);
1666 $self->cds->new({})->fill_from_artist($self)->insert;
1670 where C<fill_from_artist> is a method you specify in C<CD> which sets
1671 values in C<CD> based on the data in the C<Artist> object you pass in.
1673 =head2 Wrapping/overloading a column accessor
1677 Say you have a table "Camera" and want to associate a description
1678 with each camera. For most cameras, you'll be able to generate the description from
1679 the other columns. However, in a few special cases you may want to associate a
1680 custom description with a camera.
1684 In your database schema, define a description field in the "Camera" table that
1685 can contain text and null values.
1687 In DBIC, we'll overload the column accessor to provide a sane default if no
1688 custom description is defined. The accessor will either return or generate the
1689 description, depending on whether the field is null or not.
1691 First, in your "Camera" schema class, define the description field as follows:
1693 __PACKAGE__->add_columns(description => { accessor => '_description' });
1695 Next, we'll define the accessor-wrapper subroutine:
1700 # If there is an update to the column, we'll let the original accessor
1702 return $self->_description(@_) if @_;
1704 # Fetch the column value.
1705 my $description = $self->_description;
1707 # If there's something in the description field, then just return that.
1708 return $description if defined $description && length $descripton;
1710 # Otherwise, generate a description.
1711 return $self->generate_description;
1714 =head1 DEBUGGING AND PROFILING
1716 =head2 DBIx::Class objects with Data::Dumper
1718 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1719 be hard to find the pertinent data in all the data it can generate.
1720 Specifically, if one naively tries to use it like so,
1724 my $cd = $schema->resultset('CD')->find(1);
1727 several pages worth of data from the CD object's schema and result source will
1728 be dumped to the screen. Since usually one is only interested in a few column
1729 values of the object, this is not very helpful.
1731 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1732 it. Simply define a hook that L<Data::Dumper> will call on the object before
1733 dumping it. For example,
1740 result_source => undef,
1748 local $Data::Dumper::Freezer = '_dumper_hook';
1750 my $cd = $schema->resultset('CD')->find(1);
1752 # dumps $cd without its ResultSource
1754 If the structure of your schema is such that there is a common base class for
1755 all your table classes, simply put a method similar to C<_dumper_hook> in the
1756 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1757 will automagically clean up your data before printing it. See
1758 L<Data::Dumper/EXAMPLES> for more information.
1762 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1763 executed as well as notifications of query completion and transaction
1764 begin/commit. If you'd like to profile the SQL you can subclass the
1765 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1768 package My::Profiler;
1771 use base 'DBIx::Class::Storage::Statistics';
1773 use Time::HiRes qw(time);
1782 $self->print("Executing $sql: ".join(', ', @params)."\n");
1791 my $elapsed = sprintf("%0.4f", time() - $start);
1792 $self->print("Execution took $elapsed seconds.\n");
1798 You can then install that class as the debugging object:
1800 __PACKAGE__->storage->debugobj(new My::Profiler());
1801 __PACKAGE__->storage->debug(1);
1803 A more complicated example might involve storing each execution of SQL in an
1811 my $elapsed = time() - $start;
1812 push(@{ $calls{$sql} }, {
1818 You could then create average, high and low execution times for an SQL
1819 statement and dig down to see if certain parameters cause aberrant behavior.
1820 You might want to check out L<DBIx::Class::QueryLog> as well.
1822 =head1 STARTUP SPEED
1824 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1825 as the ORM loads all the relevant classes. This section examines
1826 techniques for reducing the startup delay.
1828 These tips are are listed in order of decreasing effectiveness - so the
1829 first tip, if applicable, should have the greatest effect on your
1832 =head2 Statically Define Your Schema
1835 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1836 classes dynamically based on the database schema then there will be a
1837 significant startup delay.
1839 For production use a statically defined schema (which can be generated
1840 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1841 the database schema once - see
1842 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1843 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1844 details on creating static schemas from a database).
1846 =head2 Move Common Startup into a Base Class
1848 Typically L<DBIx::Class> result classes start off with
1850 use base qw/DBIx::Class/;
1851 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1853 If this preamble is moved into a common base class:-
1857 use base qw/DBIx::Class/;
1858 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1861 and each result class then uses this as a base:-
1863 use base qw/MyDBICbase/;
1865 then the load_components is only performed once, which can result in a
1866 considerable startup speedup for schemas with many classes.
1868 =head2 Explicitly List Schema Result Classes
1870 The schema class will normally contain
1872 __PACKAGE__->load_classes();
1874 to load the result classes. This will use L<Module::Find|Module::Find>
1875 to find and load the appropriate modules. Explicitly defining the
1876 classes you wish to load will remove the overhead of
1877 L<Module::Find|Module::Find> and the related directory operations:
1879 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1881 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1882 syntax to load the appropriate classes there is not a direct alternative
1883 avoiding L<Module::Find|Module::Find>.
1887 =head2 Cached statements
1889 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1890 This is normally a good idea, but if too many statements are cached, the database may use too much
1891 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1892 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1894 # print all currently cached prepared statements
1895 print for keys %{$schema->storage->dbh->{CachedKids}};
1896 # get a count of currently cached prepared statements
1897 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1899 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1902 my $kids = $schema->storage->dbh->{CachedKids};
1903 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1905 But what you probably want is to expire unused statements and not those that are used frequently.
1906 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1910 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1911 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },