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('Foo')->search(
244 { distinct => [ $source->columns ] }
246 as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
250 =head2 SELECT COUNT(DISTINCT colname)
252 my $rs = $schema->resultset('Foo')->search(
256 { count => { distinct => 'colname' } }
262 my $count = $rs->next->get_column('count');
264 =head2 Grouping results
266 L<DBIx::Class> supports C<GROUP BY> as follows:
268 my $rs = $schema->resultset('Artist')->search(
272 select => [ 'name', { count => 'cds.id' } ],
273 as => [qw/ name cd_count /],
274 group_by => [qw/ name /]
279 # SELECT name, COUNT( cd.id ) FROM artist
280 # LEFT JOIN cd ON artist.id = cd.artist
283 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
284 are in any way unsure about the use of the attributes above (C< join
285 >, C< select >, C< as > and C< group_by >).
287 =head2 Subqueries (EXPERIMENTAL)
289 You can write subqueries relatively easily in DBIC.
291 my $inside_rs = $schema->resultset('Artist')->search({
292 name => [ 'Billy Joel', 'Brittany Spears' ],
295 my $rs = $schema->resultset('CD')->search({
296 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
299 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
301 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
302 The following will B<not> work:
304 my $rs = $schema->resultset('CD')->search({
305 artist_id => $inside_rs->get_column('id')->as_query,
310 Subqueries are supported in the where clause (first hashref), and in the
311 from, select, and +select attributes.
313 =head3 Correlated subqueries
315 my $cdrs = $schema->resultset('CD');
316 my $rs = $cdrs->search({
318 '=' => $cdrs->search(
319 { artistid => { '=' => \'me.artistid' } },
321 )->get_column('year')->max_rs->as_query,
325 That creates the following SQL:
327 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
330 SELECT MAX(inner.year)
332 WHERE artistid = me.artistid
337 Please note that subqueries are considered an experimental feature.
339 =head2 Predefined searches
341 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
342 and define often used searches as methods:
344 package My::DBIC::ResultSet::CD;
347 use base 'DBIx::Class::ResultSet';
349 sub search_cds_ordered {
352 return $self->search(
354 { order_by => 'name DESC' },
360 To use your resultset, first tell DBIx::Class to create an instance of it
361 for you, in your My::DBIC::Schema::CD class:
363 # class definition as normal
364 __PACKAGE__->load_components(qw/ Core /);
365 __PACKAGE__->table('cd');
367 # tell DBIC to use the custom ResultSet class
368 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
370 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
372 Then call your new method in your code:
374 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
376 =head2 Using SQL functions on the left hand side of a comparison
378 Using SQL functions on the left hand side of a comparison is generally
379 not a good idea since it requires a scan of the entire table. However,
380 it can be accomplished with C<DBIx::Class> when necessary.
382 If you do not have quoting on, simply include the function in your search
383 specification as you would any column:
385 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
387 With quoting on, or for a more portable solution, use the C<where>
390 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
394 (When the bind args ordering bug is fixed, this technique will be better
395 and can replace the one above.)
397 With quoting on, or for a more portable solution, use the C<where> and
401 where => \'YEAR(date_of_birth) = ?',
407 =head1 JOINS AND PREFETCHING
409 =head2 Using joins and prefetch
411 You can use the C<join> attribute to allow searching on, or sorting your
412 results by, one or more columns in a related table. To return all CDs matching
413 a particular artist name:
415 my $rs = $schema->resultset('CD')->search(
417 'artist.name' => 'Bob Marley'
420 join => 'artist', # join the artist table
425 # SELECT cd.* FROM cd
426 # JOIN artist ON cd.artist = artist.id
427 # WHERE artist.name = 'Bob Marley'
429 If required, you can now sort on any column in the related tables by including
430 it in your C<order_by> attribute:
432 my $rs = $schema->resultset('CD')->search(
434 'artist.name' => 'Bob Marley'
438 order_by => [qw/ artist.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 'artist.name' => 'Bob Marley'
479 order_by => [qw/ artist.name /],
480 prefetch => 'artist' # 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 C<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 Dynamic Sub-classing DBIx::Class proxy classes
718 AKA multi-class object inflation from one table
720 L<DBIx::Class> classes are proxy classes, therefore some different
721 techniques need to be employed for more than basic subclassing. In
722 this example we have a single user table that carries a boolean bit
723 for admin. We would like like to give the admin users
724 objects(L<DBIx::Class::Row>) the same methods as a regular user but
725 also special admin only methods. It doesn't make sense to create two
726 seperate proxy-class files for this. We would be copying all the user
727 methods into the Admin class. There is a cleaner way to accomplish
730 Overriding the C<inflate_result> method within the User proxy-class
731 gives us the effect we want. This method is called by
732 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
733 grab the object being returned, inspect the values we are looking for,
734 bless it if it's an admin object, and then return it. See the example
741 use base qw/DBIx::Class::Schema/;
743 __PACKAGE__->load_namespaces;
746 B<Proxy-Class definitions>
748 package My::Schema::Result::User;
752 use base qw/DBIx::Class/;
754 ### Defined what our admin class is for ensure_class_loaded
755 my $admin_class = __PACKAGE__ . '::Admin';
757 __PACKAGE__->load_components(qw/Core/);
759 __PACKAGE__->table('users');
761 __PACKAGE__->add_columns(qw/user_id email password
762 firstname lastname active
765 __PACKAGE__->set_primary_key('user_id');
769 my $ret = $self->next::method(@_);
770 if( $ret->admin ) {### If this is an admin rebless for extra functions
771 $self->ensure_class_loaded( $admin_class );
772 bless $ret, $admin_class;
778 print "I am a regular user.\n";
783 package My::Schema::Result::User::Admin;
787 use base qw/My::Schema::Result::User/;
791 print "I am an admin.\n";
797 print "I am doing admin stuff\n";
807 my $user_data = { email => 'someguy@place.com',
811 my $admin_data = { email => 'someadmin@adminplace.com',
815 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
817 $schema->resultset('User')->create( $user_data );
818 $schema->resultset('User')->create( $admin_data );
820 ### Now we search for them
821 my $user = $schema->resultset('User')->single( $user_data );
822 my $admin = $schema->resultset('User')->single( $admin_data );
824 print ref $user, "\n";
825 print ref $admin, "\n";
827 print $user->password , "\n"; # pass1
828 print $admin->password , "\n";# pass2; inherited from User
829 print $user->hello , "\n";# I am a regular user.
830 print $admin->hello, "\n";# I am an admin.
832 ### The statement below will NOT print
833 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
834 ### The statement below will print
835 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
837 =head2 Skip row object creation for faster results
839 DBIx::Class is not built for speed, it's built for convenience and
840 ease of use, but sometimes you just need to get the data, and skip the
843 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
845 my $rs = $schema->resultset('CD');
847 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
849 my $hash_ref = $rs->find(1);
853 Beware, changing the Result class using
854 L<DBIx::Class::ResultSet/result_class> will replace any existing class
855 completely including any special components loaded using
856 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
858 =head2 Get raw data for blindingly fast results
860 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
861 above is not fast enough for you, you can use a DBIx::Class to return values
862 exactly as they come out of the database with none of the convenience methods
865 This is used like so:
867 my $cursor = $rs->cursor
868 while (my @vals = $cursor->next) {
869 # use $val[0..n] here
872 You will need to map the array offsets to particular columns (you can
873 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
875 =head1 RESULTSET OPERATIONS
877 =head2 Getting Schema from a ResultSet
879 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
881 $rs->result_source->schema
883 =head2 Getting Columns Of Data
887 If you want to find the sum of a particular column there are several
888 ways, the obvious one is to use search:
890 my $rs = $schema->resultset('Items')->search(
893 select => [ { sum => 'Cost' } ],
894 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
897 my $tc = $rs->first->get_column('total_cost');
899 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
900 returned when you ask the C<ResultSet> for a column using
903 my $cost = $schema->resultset('Items')->get_column('Cost');
906 With this you can also do:
908 my $minvalue = $cost->min;
909 my $maxvalue = $cost->max;
911 Or just iterate through the values of this column only:
913 while ( my $c = $cost->next ) {
917 foreach my $c ($cost->all) {
921 C<ResultSetColumn> only has a limited number of built-in functions, if
922 you need one that it doesn't have, then you can use the C<func> method
925 my $avg = $cost->func('AVERAGE');
927 This will cause the following SQL statement to be run:
929 SELECT AVERAGE(Cost) FROM Items me
931 Which will of course only work if your database supports this function.
932 See L<DBIx::Class::ResultSetColumn> for more documentation.
934 =head2 Creating a result set from a set of rows
936 Sometimes you have a (set of) row objects that you want to put into a
937 resultset without the need to hit the DB again. You can do that by using the
938 L<set_cache|DBIx::Class::Resultset/set_cache> method:
940 my @uploadable_groups;
941 while (my $group = $groups->next) {
942 if ($group->can_upload($self)) {
943 push @uploadable_groups, $group;
946 my $new_rs = $self->result_source->resultset;
947 $new_rs->set_cache(\@uploadable_groups);
951 =head1 USING RELATIONSHIPS
953 =head2 Create a new row in a related table
955 my $author = $book->create_related('author', { name => 'Fred'});
957 =head2 Search in a related table
959 Only searches for books named 'Titanic' by the author in $author.
961 my $books_rs = $author->search_related('books', { name => 'Titanic' });
963 =head2 Delete data in a related table
965 Deletes only the book named Titanic by the author in $author.
967 $author->delete_related('books', { name => 'Titanic' });
969 =head2 Ordering a relationship result set
971 If you always want a relation to be ordered, you can specify this when you
972 create the relationship.
974 To order C<< $book->pages >> by descending page_number, create the relation
977 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
979 =head2 Filtering a relationship result set
981 If you want to get a filtered result set, you can just add add to $attr as follows:
983 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
985 =head2 Many-to-many relationships
987 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
990 use base 'DBIx::Class';
991 __PACKAGE__->load_components('Core');
992 __PACKAGE__->table('user');
993 __PACKAGE__->add_columns(qw/id name/);
994 __PACKAGE__->set_primary_key('id');
995 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
996 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
998 package My::UserAddress;
999 use base 'DBIx::Class';
1000 __PACKAGE__->load_components('Core');
1001 __PACKAGE__->table('user_address');
1002 __PACKAGE__->add_columns(qw/user address/);
1003 __PACKAGE__->set_primary_key(qw/user address/);
1004 __PACKAGE__->belongs_to('user' => 'My::User');
1005 __PACKAGE__->belongs_to('address' => 'My::Address');
1007 package My::Address;
1008 use base 'DBIx::Class';
1009 __PACKAGE__->load_components('Core');
1010 __PACKAGE__->table('address');
1011 __PACKAGE__->add_columns(qw/id street town area_code country/);
1012 __PACKAGE__->set_primary_key('id');
1013 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1014 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1016 $rs = $user->addresses(); # get all addresses for a user
1017 $rs = $address->users(); # get all users for an address
1019 =head2 Relationships across DB schemas
1021 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1022 is easy as long as the schemas themselves are all accessible via the same DBI
1023 connection. In most cases, this means that they are on the same database host
1024 as each other and your connecting database user has the proper permissions to them.
1026 To accomplish this one only needs to specify the DB schema name in the table
1027 declaration, like so...
1029 package MyDatabase::Main::Artist;
1030 use base qw/DBIx::Class/;
1031 __PACKAGE__->load_components(qw/PK::Auto Core/);
1033 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1035 __PACKAGE__->add_columns(qw/ artistid name /);
1036 __PACKAGE__->set_primary_key('artistid');
1037 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1041 Whatever string you specify there will be used to build the "FROM" clause in SQL
1044 The big drawback to this is you now have DB schema names hardcoded in your
1045 class files. This becomes especially troublesome if you have multiple instances
1046 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1047 the DB schemas are named based on the environment (e.g. database1_dev).
1049 However, one can dynamically "map" to the proper DB schema by overriding the
1050 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1051 building a renaming facility, like so:
1053 package MyDatabase::Schema;
1056 extends 'DBIx::Class::Schema';
1058 around connection => sub {
1059 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1061 my $postfix = delete $attr->{schema_name_postfix};
1066 $self->append_db_name($postfix);
1070 sub append_db_name {
1071 my ( $self, $postfix ) = @_;
1075 { $_->name =~ /^\w+\./mx }
1077 { $self->source($_) }
1080 foreach my $source (@sources_with_db) {
1081 my $name = $source->name;
1082 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1084 $source->name($name);
1090 By overridding the L<connection|DBIx::Class::Schama/connection>
1091 method and extracting a custom option from the provided \%attr hashref one can
1092 then simply iterate over all the Schema's ResultSources, renaming them as
1095 To use this facility, simply add or modify the \%attr hashref that is passed to
1096 L<connection|DBIx::Class::Schama/connect>, as follows:
1099 = MyDatabase::Schema->connect(
1104 schema_name_postfix => '_dev'
1105 # ... Other options as desired ...
1108 Obviously, one could accomplish even more advanced mapping via a hash map or a
1113 As of version 0.04001, there is improved transaction support in
1114 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1115 example of the recommended way to use it:
1117 my $genus = $schema->resultset('Genus')->find(12);
1119 my $coderef2 = sub {
1124 my $coderef1 = sub {
1125 $genus->add_to_species({ name => 'troglodyte' });
1128 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1129 return $genus->species;
1134 $rs = $schema->txn_do($coderef1);
1137 if ($@) { # Transaction failed
1138 die "the sky is falling!" #
1139 if ($@ =~ /Rollback failed/); # Rollback failed
1141 deal_with_failed_transaction();
1144 Nested transactions will work as expected. That is, only the outermost
1145 transaction will actually issue a commit to the $dbh, and a rollback
1146 at any level of any transaction will cause the entire nested
1147 transaction to fail. Support for savepoints and for true nested
1148 transactions (for databases that support them) will hopefully be added
1153 =head2 Creating Schemas From An Existing Database
1155 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1156 L<DBIx::Class::Schema> and associated sources by examining the database.
1158 The recommend way of achieving this is to use the
1159 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1161 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1162 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1164 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1165 source definitions for all the tables found in the C<foo> database.
1167 =head2 Creating DDL SQL
1169 The following functionality requires you to have L<SQL::Translator>
1170 (also known as "SQL Fairy") installed.
1172 To create a set of database-specific .sql files for the above schema:
1174 my $schema = My::Schema->connect($dsn);
1175 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1180 By default this will create schema files in the current directory, for
1181 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1183 To create a new database using the schema:
1185 my $schema = My::Schema->connect($dsn);
1186 $schema->deploy({ add_drop_tables => 1});
1188 To import created .sql files using the mysql client:
1190 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1192 To create C<ALTER TABLE> conversion scripts to update a database to a
1193 newer version of your schema at a later point, first set a new
1194 C<$VERSION> in your Schema file, then:
1196 my $schema = My::Schema->connect($dsn);
1197 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1203 This will produce new database-specific .sql files for the new version
1204 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1205 requires that the files for 0.1 as created above are available in the
1206 given directory to diff against.
1208 =head2 Select from dual
1210 Dummy tables are needed by some databases to allow calling functions
1211 or expressions that aren't based on table content, for examples of how
1212 this applies to various database types, see:
1213 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1215 Note: If you're using Oracles dual table don't B<ever> do anything
1216 other than a select, if you CRUD on your dual table you *will* break
1219 Make a table class as you would for any other table
1221 package MyAppDB::Dual;
1224 use base 'DBIx::Class';
1225 __PACKAGE__->load_components("Core");
1226 __PACKAGE__->table("Dual");
1227 __PACKAGE__->add_columns(
1229 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1232 Once you've loaded your table class select from it using C<select>
1233 and C<as> instead of C<columns>
1235 my $rs = $schema->resultset('Dual')->search(undef,
1236 { select => [ 'sydate' ],
1241 All you have to do now is be careful how you access your resultset, the below
1242 will not work because there is no column called 'now' in the Dual table class
1244 while (my $dual = $rs->next) {
1245 print $dual->now."\n";
1247 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1249 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1250 your Dual class for whatever you wanted to select from dual, but that's just
1251 silly, instead use C<get_column>
1253 while (my $dual = $rs->next) {
1254 print $dual->get_column('now')."\n";
1259 my $cursor = $rs->cursor;
1260 while (my @vals = $cursor->next) {
1261 print $vals[0]."\n";
1264 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1265 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1266 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1267 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1268 L<SQL::Translator> to not create table dual:
1271 add_drop_table => 1,
1272 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1274 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1276 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1278 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1279 while ( my $dual = $rs->next ) {
1280 print $dual->{now}."\n";
1283 Here are some example C<select> conditions to illustrate the different syntax
1284 you could use for doing stuff like
1285 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1287 # get a sequence value
1288 select => [ 'A_SEQ.nextval' ],
1290 # get create table sql
1291 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1293 # get a random num between 0 and 100
1294 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1297 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1300 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1302 # which day of the week were you born on?
1303 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1305 # select 16 rows from dual
1306 select => [ "'hello'" ],
1308 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1312 =head2 Adding Indexes And Functions To Your SQL
1314 Often you will want indexes on columns on your table to speed up searching. To
1315 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1316 class (refer to the advanced
1317 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1318 to share a hook between multiple sources):
1320 package My::Schema::Result::Artist;
1322 __PACKAGE__->table('artist');
1323 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1325 sub sqlt_deploy_hook {
1326 my ($self, $sqlt_table) = @_;
1328 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1333 Sometimes you might want to change the index depending on the type of the
1334 database for which SQL is being generated:
1336 my ($db_type = $sqlt_table->schema->translator->producer_type)
1337 =~ s/^SQL::Translator::Producer:://;
1339 You can also add hooks to the schema level to stop certain tables being
1346 sub sqlt_deploy_hook {
1347 my ($self, $sqlt_schema) = @_;
1349 $sqlt_schema->drop_table('table_name');
1352 You could also add views, procedures or triggers to the output using
1353 L<SQL::Translator::Schema/add_view>,
1354 L<SQL::Translator::Schema/add_procedure> or
1355 L<SQL::Translator::Schema/add_trigger>.
1358 =head2 Schema versioning
1360 The following example shows simplistically how you might use DBIx::Class to
1361 deploy versioned schemas to your customers. The basic process is as follows:
1367 Create a DBIx::Class schema
1379 Modify schema to change functionality
1383 Deploy update to customers
1387 B<Create a DBIx::Class schema>
1389 This can either be done manually, or generated from an existing database as
1390 described under L</Creating Schemas From An Existing Database>
1394 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1396 B<Deploy to customers>
1398 There are several ways you could deploy your schema. These are probably
1399 beyond the scope of this recipe, but might include:
1405 Require customer to apply manually using their RDBMS.
1409 Package along with your app, making database dump/schema update/tests
1410 all part of your install.
1414 B<Modify the schema to change functionality>
1416 As your application evolves, it may be necessary to modify your schema
1417 to change functionality. Once the changes are made to your schema in
1418 DBIx::Class, export the modified schema and the conversion scripts as
1419 in L</Creating DDL SQL>.
1421 B<Deploy update to customers>
1423 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1424 Schema class. This will add a new table to your database called
1425 C<dbix_class_schema_vesion> which will keep track of which version is installed
1426 and warn if the user trys to run a newer schema version than the
1427 database thinks it has.
1429 Alternatively, you can send the conversion sql scripts to your
1432 =head2 Setting quoting for the generated SQL.
1434 If the database contains column names with spaces and/or reserved words, they
1435 need to be quoted in the SQL queries. This is done using:
1437 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1438 __PACKAGE__->storage->sql_maker->name_sep('.');
1440 The first sets the quote characters. Either a pair of matching
1441 brackets, or a C<"> or C<'>:
1443 __PACKAGE__->storage->sql_maker->quote_char('"');
1445 Check the documentation of your database for the correct quote
1446 characters to use. C<name_sep> needs to be set to allow the SQL
1447 generator to put the quotes the correct place.
1449 In most cases you should set these as part of the arguments passed to
1450 L<DBIx::Class::Schema/connect>:
1452 my $schema = My::Schema->connect(
1462 =head2 Setting limit dialect for SQL::Abstract::Limit
1464 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1465 the remote SQL server by looking at the database handle. This is a
1466 common problem when using the DBD::JDBC, since the DBD-driver only
1467 know that in has a Java-driver available, not which JDBC driver the
1468 Java component has loaded. This specifically sets the limit_dialect
1469 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1472 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1474 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1475 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1477 The limit dialect can also be set at connect time by specifying a
1478 C<limit_dialect> key in the final hash as shown above.
1480 =head2 Working with PostgreSQL array types
1482 You can also assign values to PostgreSQL array columns by passing array
1483 references in the C<\%columns> (C<\%vals>) hashref of the
1484 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1487 $resultset->create({
1488 numbers => [1, 2, 3]
1493 numbers => [1, 2, 3]
1500 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1501 methods) you cannot directly use array references (since this is interpreted as
1502 a list of values to be C<OR>ed), but you can use the following syntax to force
1503 passing them as bind values:
1507 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1511 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1512 placeholders and bind values (subqueries)> for more explanation. Note that
1513 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1514 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1515 arrayrefs together with the column name, like this: C<< [column_name => value]
1518 =head1 BOOTSTRAPPING/MIGRATING
1520 =head2 Easy migration from class-based to schema-based setup
1522 You want to start using the schema-based approach to L<DBIx::Class>
1523 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1524 of existing classes that you don't want to move by hand. Try this nifty script
1528 use SQL::Translator;
1530 my $schema = MyDB->schema_instance;
1532 my $translator = SQL::Translator->new(
1533 debug => $debug || 0,
1534 trace => $trace || 0,
1535 no_comments => $no_comments || 0,
1536 show_warnings => $show_warnings || 0,
1537 add_drop_table => $add_drop_table || 0,
1538 validate => $validate || 0,
1540 'DBIx::Schema' => $schema,
1543 'prefix' => 'My::Schema',
1547 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1548 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1550 my $output = $translator->translate(@args) or die
1551 "Error: " . $translator->error;
1555 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1556 namespace, which is currently left as an exercise for the reader.
1558 =head1 OVERLOADING METHODS
1560 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1561 method calls, useful for things like default values and triggers. You have to
1562 use calls to C<next::method> to overload methods. More information on using
1563 L<Class::C3> with L<DBIx::Class> can be found in
1564 L<DBIx::Class::Manual::Component>.
1566 =head2 Setting default values for a row
1568 It's as simple as overriding the C<new> method. Note the use of
1572 my ( $class, $attrs ) = @_;
1574 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1576 my $new = $class->next::method($attrs);
1581 For more information about C<next::method>, look in the L<Class::C3>
1582 documentation. See also L<DBIx::Class::Manual::Component> for more
1583 ways to write your own base classes to do this.
1585 People looking for ways to do "triggers" with DBIx::Class are probably
1586 just looking for this.
1588 =head2 Changing one field whenever another changes
1590 For example, say that you have three columns, C<id>, C<number>, and
1591 C<squared>. You would like to make changes to C<number> and have
1592 C<squared> be automagically set to the value of C<number> squared.
1593 You can accomplish this by overriding C<store_column>:
1596 my ( $self, $name, $value ) = @_;
1597 if ($name eq 'number') {
1598 $self->squared($value * $value);
1600 $self->next::method($name, $value);
1603 Note that the hard work is done by the call to C<next::method>, which
1604 redispatches your call to store_column in the superclass(es).
1606 =head2 Automatically creating related objects
1608 You might have a class C<Artist> which has many C<CD>s. Further, if you
1609 want to create a C<CD> object every time you insert an C<Artist> object.
1610 You can accomplish this by overriding C<insert> on your objects:
1613 my ( $self, @args ) = @_;
1614 $self->next::method(@args);
1615 $self->cds->new({})->fill_from_artist($self)->insert;
1619 where C<fill_from_artist> is a method you specify in C<CD> which sets
1620 values in C<CD> based on the data in the C<Artist> object you pass in.
1622 =head2 Wrapping/overloading a column accessor
1626 Say you have a table "Camera" and want to associate a description
1627 with each camera. For most cameras, you'll be able to generate the description from
1628 the other columns. However, in a few special cases you may want to associate a
1629 custom description with a camera.
1633 In your database schema, define a description field in the "Camera" table that
1634 can contain text and null values.
1636 In DBIC, we'll overload the column accessor to provide a sane default if no
1637 custom description is defined. The accessor will either return or generate the
1638 description, depending on whether the field is null or not.
1640 First, in your "Camera" schema class, define the description field as follows:
1642 __PACKAGE__->add_columns(description => { accessor => '_description' });
1644 Next, we'll define the accessor-wrapper subroutine:
1649 # If there is an update to the column, we'll let the original accessor
1651 return $self->_description(@_) if @_;
1653 # Fetch the column value.
1654 my $description = $self->_description;
1656 # If there's something in the description field, then just return that.
1657 return $description if defined $description && length $descripton;
1659 # Otherwise, generate a description.
1660 return $self->generate_description;
1663 =head1 DEBUGGING AND PROFILING
1665 =head2 DBIx::Class objects with Data::Dumper
1667 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1668 be hard to find the pertinent data in all the data it can generate.
1669 Specifically, if one naively tries to use it like so,
1673 my $cd = $schema->resultset('CD')->find(1);
1676 several pages worth of data from the CD object's schema and result source will
1677 be dumped to the screen. Since usually one is only interested in a few column
1678 values of the object, this is not very helpful.
1680 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1681 it. Simply define a hook that L<Data::Dumper> will call on the object before
1682 dumping it. For example,
1689 result_source => undef,
1697 local $Data::Dumper::Freezer = '_dumper_hook';
1699 my $cd = $schema->resultset('CD')->find(1);
1701 # dumps $cd without its ResultSource
1703 If the structure of your schema is such that there is a common base class for
1704 all your table classes, simply put a method similar to C<_dumper_hook> in the
1705 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1706 will automagically clean up your data before printing it. See
1707 L<Data::Dumper/EXAMPLES> for more information.
1711 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1712 executed as well as notifications of query completion and transaction
1713 begin/commit. If you'd like to profile the SQL you can subclass the
1714 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1717 package My::Profiler;
1720 use base 'DBIx::Class::Storage::Statistics';
1722 use Time::HiRes qw(time);
1731 $self->print("Executing $sql: ".join(', ', @params)."\n");
1740 my $elapsed = sprintf("%0.4f", time() - $start);
1741 $self->print("Execution took $elapsed seconds.\n");
1747 You can then install that class as the debugging object:
1749 __PACKAGE__->storage->debugobj(new My::Profiler());
1750 __PACKAGE__->storage->debug(1);
1752 A more complicated example might involve storing each execution of SQL in an
1760 my $elapsed = time() - $start;
1761 push(@{ $calls{$sql} }, {
1767 You could then create average, high and low execution times for an SQL
1768 statement and dig down to see if certain parameters cause aberrant behavior.
1769 You might want to check out L<DBIx::Class::QueryLog> as well.
1771 =head1 STARTUP SPEED
1773 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1774 as the ORM loads all the relevant classes. This section examines
1775 techniques for reducing the startup delay.
1777 These tips are are listed in order of decreasing effectiveness - so the
1778 first tip, if applicable, should have the greatest effect on your
1781 =head2 Statically Define Your Schema
1784 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1785 classes dynamically based on the database schema then there will be a
1786 significant startup delay.
1788 For production use a statically defined schema (which can be generated
1789 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1790 the database schema once - see
1791 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1792 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1793 details on creating static schemas from a database).
1795 =head2 Move Common Startup into a Base Class
1797 Typically L<DBIx::Class> result classes start off with
1799 use base qw/DBIx::Class/;
1800 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1802 If this preamble is moved into a common base class:-
1806 use base qw/DBIx::Class/;
1807 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1810 and each result class then uses this as a base:-
1812 use base qw/MyDBICbase/;
1814 then the load_components is only performed once, which can result in a
1815 considerable startup speedup for schemas with many classes.
1817 =head2 Explicitly List Schema Result Classes
1819 The schema class will normally contain
1821 __PACKAGE__->load_classes();
1823 to load the result classes. This will use L<Module::Find|Module::Find>
1824 to find and load the appropriate modules. Explicitly defining the
1825 classes you wish to load will remove the overhead of
1826 L<Module::Find|Module::Find> and the related directory operations:-
1828 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1830 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1831 syntax to load the appropriate classes there is not a direct alternative
1832 avoiding L<Module::Find|Module::Find>.
1836 =head2 Cached statements
1838 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1839 This is normally a good idea, but if too many statements are cached, the database may use too much
1840 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1841 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1843 # print all currently cached prepared statements
1844 print for keys %{$schema->storage->dbh->{CachedKids}};
1845 # get a count of currently cached prepared statements
1846 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1848 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1851 my $kids = $schema->storage->dbh->{CachedKids};
1852 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1854 But what you probably want is to expire unused statements and not those that are used frequently.
1855 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1859 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1860 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },