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 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
501 C<has_many> relationships.
503 Also note that C<prefetch> should only be used when you know you will
504 definitely use data from a related table. Pre-fetching related tables when you
505 only need columns from the main table will make performance worse!
507 =head2 Multiple joins
509 In the examples above, the C<join> attribute was a scalar. If you
510 pass an array reference instead, you can join to multiple tables. In
511 this example, we want to limit the search further, using
514 # Relationships defined elsewhere:
515 # CD->belongs_to('artist' => 'Artist');
516 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
517 my $rs = $schema->resultset('CD')->search(
519 'artist.name' => 'Bob Marley'
520 'liner_notes.notes' => { 'like', '%some text%' },
523 join => [qw/ artist liner_notes /],
524 order_by => [qw/ artist.name /],
529 # SELECT cd.*, artist.*, liner_notes.* FROM cd
530 # JOIN artist ON cd.artist = artist.id
531 # JOIN liner_notes ON cd.id = liner_notes.cd
532 # WHERE artist.name = 'Bob Marley'
533 # ORDER BY artist.name
535 =head2 Multi-step joins
537 Sometimes you want to join more than one relationship deep. In this example,
538 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
539 contain a specific string:
541 # Relationships defined elsewhere:
542 # Artist->has_many('cds' => 'CD', 'artist');
543 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
545 my $rs = $schema->resultset('Artist')->search(
547 'liner_notes.notes' => { 'like', '%some text%' },
551 'cds' => 'liner_notes'
557 # SELECT artist.* FROM artist
558 # LEFT JOIN cd ON artist.id = cd.artist
559 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
560 # WHERE liner_notes.notes LIKE '%some text%'
562 Joins can be nested to an arbitrary level. So if we decide later that we
563 want to reduce the number of Artists returned based on who wrote the liner
566 # Relationship defined elsewhere:
567 # LinerNotes->belongs_to('author' => 'Person');
569 my $rs = $schema->resultset('Artist')->search(
571 'liner_notes.notes' => { 'like', '%some text%' },
572 'author.name' => 'A. Writer'
577 'liner_notes' => 'author'
584 # SELECT artist.* FROM artist
585 # LEFT JOIN cd ON artist.id = cd.artist
586 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
587 # LEFT JOIN author ON author.id = liner_notes.author
588 # WHERE liner_notes.notes LIKE '%some text%'
589 # AND author.name = 'A. Writer'
591 =head2 Multi-step and multiple joins
593 With various combinations of array and hash references, you can join
594 tables in any combination you desire. For example, to join Artist to
595 CD and Concert, and join CD to LinerNotes:
597 # Relationships defined elsewhere:
598 # Artist->has_many('concerts' => 'Concert', 'artist');
600 my $rs = $schema->resultset('Artist')->search(
613 # SELECT artist.* FROM artist
614 # LEFT JOIN cd ON artist.id = cd.artist
615 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
616 # LEFT JOIN concert ON artist.id = concert.artist
618 =head2 Multi-step prefetch
620 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
621 deep using the same syntax as a multi-step join:
623 my $rs = $schema->resultset('Tag')->search(
633 # SELECT tag.*, cd.*, artist.* FROM tag
634 # JOIN cd ON tag.cd = cd.id
635 # JOIN artist ON cd.artist = artist.id
637 Now accessing our C<cd> and C<artist> relationships does not need additional
640 my $tag = $rs->first;
641 print $tag->cd->artist->name;
643 =head1 ROW-LEVEL OPERATIONS
645 =head2 Retrieving a row object's Schema
647 It is possible to get a Schema object from a row object like so:
649 my $schema = $cd->result_source->schema;
650 # use the schema as normal:
651 my $artist_rs = $schema->resultset('Artist');
653 This can be useful when you don't want to pass around a Schema object to every
656 =head2 Getting the value of the primary key for the last database insert
658 AKA getting last_insert_id
660 If you are using PK::Auto (which is a core component as of 0.07), this is
663 my $foo = $rs->create(\%blah);
665 my $id = $foo->id; # foo->my_primary_key_field will also work.
667 If you are not using autoincrementing primary keys, this will probably
668 not work, but then you already know the value of the last primary key anyway.
670 =head2 Stringification
672 Employ the standard stringification technique by using the C<overload>
675 To make an object stringify itself as a single column, use something
676 like this (replace C<name> with the column/method of your choice):
678 use overload '""' => sub { shift->name}, fallback => 1;
680 For more complex stringification, you can use an anonymous subroutine:
682 use overload '""' => sub { $_[0]->name . ", " .
683 $_[0]->address }, fallback => 1;
685 =head3 Stringification Example
687 Suppose we have two tables: C<Product> and C<Category>. The table
690 Product(id, Description, category)
691 Category(id, Description)
693 C<category> is a foreign key into the Category table.
695 If you have a Product object C<$obj> and write something like
699 things will not work as expected.
701 To obtain, for example, the category description, you should add this
702 method to the class defining the Category table:
704 use overload "" => sub {
707 return $self->Description;
710 =head2 Want to know if find_or_create found or created a row?
712 Just use C<find_or_new> instead, then check C<in_storage>:
714 my $obj = $rs->find_or_new({ blah => 'blarg' });
715 unless ($obj->in_storage) {
717 # do whatever else you wanted if it was a new row
720 =head2 Dynamic Sub-classing DBIx::Class proxy classes
722 AKA multi-class object inflation from one table
724 L<DBIx::Class> classes are proxy classes, therefore some different
725 techniques need to be employed for more than basic subclassing. In
726 this example we have a single user table that carries a boolean bit
727 for admin. We would like like to give the admin users
728 objects(L<DBIx::Class::Row>) the same methods as a regular user but
729 also special admin only methods. It doesn't make sense to create two
730 seperate proxy-class files for this. We would be copying all the user
731 methods into the Admin class. There is a cleaner way to accomplish
734 Overriding the C<inflate_result> method within the User proxy-class
735 gives us the effect we want. This method is called by
736 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
737 grab the object being returned, inspect the values we are looking for,
738 bless it if it's an admin object, and then return it. See the example
745 use base qw/DBIx::Class::Schema/;
747 __PACKAGE__->load_namespaces;
750 B<Proxy-Class definitions>
752 package My::Schema::Result::User;
756 use base qw/DBIx::Class/;
758 ### Defined what our admin class is for ensure_class_loaded
759 my $admin_class = __PACKAGE__ . '::Admin';
761 __PACKAGE__->load_components(qw/Core/);
763 __PACKAGE__->table('users');
765 __PACKAGE__->add_columns(qw/user_id email password
766 firstname lastname active
769 __PACKAGE__->set_primary_key('user_id');
773 my $ret = $self->next::method(@_);
774 if( $ret->admin ) {### If this is an admin rebless for extra functions
775 $self->ensure_class_loaded( $admin_class );
776 bless $ret, $admin_class;
782 print "I am a regular user.\n";
787 package My::Schema::Result::User::Admin;
791 use base qw/My::Schema::Result::User/;
795 print "I am an admin.\n";
801 print "I am doing admin stuff\n";
811 my $user_data = { email => 'someguy@place.com',
815 my $admin_data = { email => 'someadmin@adminplace.com',
819 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
821 $schema->resultset('User')->create( $user_data );
822 $schema->resultset('User')->create( $admin_data );
824 ### Now we search for them
825 my $user = $schema->resultset('User')->single( $user_data );
826 my $admin = $schema->resultset('User')->single( $admin_data );
828 print ref $user, "\n";
829 print ref $admin, "\n";
831 print $user->password , "\n"; # pass1
832 print $admin->password , "\n";# pass2; inherited from User
833 print $user->hello , "\n";# I am a regular user.
834 print $admin->hello, "\n";# I am an admin.
836 ### The statement below will NOT print
837 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
838 ### The statement below will print
839 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
841 =head2 Skip row object creation for faster results
843 DBIx::Class is not built for speed, it's built for convenience and
844 ease of use, but sometimes you just need to get the data, and skip the
847 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
849 my $rs = $schema->resultset('CD');
851 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
853 my $hash_ref = $rs->find(1);
857 Beware, changing the Result class using
858 L<DBIx::Class::ResultSet/result_class> will replace any existing class
859 completely including any special components loaded using
860 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
862 =head2 Get raw data for blindingly fast results
864 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
865 above is not fast enough for you, you can use a DBIx::Class to return values
866 exactly as they come out of the database with none of the convenience methods
869 This is used like so:
871 my $cursor = $rs->cursor
872 while (my @vals = $cursor->next) {
873 # use $val[0..n] here
876 You will need to map the array offsets to particular columns (you can
877 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
879 =head1 RESULTSET OPERATIONS
881 =head2 Getting Schema from a ResultSet
883 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
885 $rs->result_source->schema
887 =head2 Getting Columns Of Data
891 If you want to find the sum of a particular column there are several
892 ways, the obvious one is to use search:
894 my $rs = $schema->resultset('Items')->search(
897 select => [ { sum => 'Cost' } ],
898 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
901 my $tc = $rs->first->get_column('total_cost');
903 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
904 returned when you ask the C<ResultSet> for a column using
907 my $cost = $schema->resultset('Items')->get_column('Cost');
910 With this you can also do:
912 my $minvalue = $cost->min;
913 my $maxvalue = $cost->max;
915 Or just iterate through the values of this column only:
917 while ( my $c = $cost->next ) {
921 foreach my $c ($cost->all) {
925 C<ResultSetColumn> only has a limited number of built-in functions, if
926 you need one that it doesn't have, then you can use the C<func> method
929 my $avg = $cost->func('AVERAGE');
931 This will cause the following SQL statement to be run:
933 SELECT AVERAGE(Cost) FROM Items me
935 Which will of course only work if your database supports this function.
936 See L<DBIx::Class::ResultSetColumn> for more documentation.
938 =head2 Creating a result set from a set of rows
940 Sometimes you have a (set of) row objects that you want to put into a
941 resultset without the need to hit the DB again. You can do that by using the
942 L<set_cache|DBIx::Class::Resultset/set_cache> method:
944 my @uploadable_groups;
945 while (my $group = $groups->next) {
946 if ($group->can_upload($self)) {
947 push @uploadable_groups, $group;
950 my $new_rs = $self->result_source->resultset;
951 $new_rs->set_cache(\@uploadable_groups);
955 =head1 USING RELATIONSHIPS
957 =head2 Create a new row in a related table
959 my $author = $book->create_related('author', { name => 'Fred'});
961 =head2 Search in a related table
963 Only searches for books named 'Titanic' by the author in $author.
965 my $books_rs = $author->search_related('books', { name => 'Titanic' });
967 =head2 Delete data in a related table
969 Deletes only the book named Titanic by the author in $author.
971 $author->delete_related('books', { name => 'Titanic' });
973 =head2 Ordering a relationship result set
975 If you always want a relation to be ordered, you can specify this when you
976 create the relationship.
978 To order C<< $book->pages >> by descending page_number, create the relation
981 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
983 =head2 Filtering a relationship result set
985 If you want to get a filtered result set, you can just add add to $attr as follows:
987 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
989 =head2 Many-to-many relationships
991 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
994 use base 'DBIx::Class';
995 __PACKAGE__->load_components('Core');
996 __PACKAGE__->table('user');
997 __PACKAGE__->add_columns(qw/id name/);
998 __PACKAGE__->set_primary_key('id');
999 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1000 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1002 package My::UserAddress;
1003 use base 'DBIx::Class';
1004 __PACKAGE__->load_components('Core');
1005 __PACKAGE__->table('user_address');
1006 __PACKAGE__->add_columns(qw/user address/);
1007 __PACKAGE__->set_primary_key(qw/user address/);
1008 __PACKAGE__->belongs_to('user' => 'My::User');
1009 __PACKAGE__->belongs_to('address' => 'My::Address');
1011 package My::Address;
1012 use base 'DBIx::Class';
1013 __PACKAGE__->load_components('Core');
1014 __PACKAGE__->table('address');
1015 __PACKAGE__->add_columns(qw/id street town area_code country/);
1016 __PACKAGE__->set_primary_key('id');
1017 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1018 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1020 $rs = $user->addresses(); # get all addresses for a user
1021 $rs = $address->users(); # get all users for an address
1023 =head2 Relationships across DB schemas
1025 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1026 is easy as long as the schemas themselves are all accessible via the same DBI
1027 connection. In most cases, this means that they are on the same database host
1028 as each other and your connecting database user has the proper permissions to them.
1030 To accomplish this one only needs to specify the DB schema name in the table
1031 declaration, like so...
1033 package MyDatabase::Main::Artist;
1034 use base qw/DBIx::Class/;
1035 __PACKAGE__->load_components(qw/PK::Auto Core/);
1037 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1039 __PACKAGE__->add_columns(qw/ artistid name /);
1040 __PACKAGE__->set_primary_key('artistid');
1041 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1045 Whatever string you specify there will be used to build the "FROM" clause in SQL
1048 The big drawback to this is you now have DB schema names hardcoded in your
1049 class files. This becomes especially troublesome if you have multiple instances
1050 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1051 the DB schemas are named based on the environment (e.g. database1_dev).
1053 However, one can dynamically "map" to the proper DB schema by overriding the
1054 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1055 building a renaming facility, like so:
1057 package MyDatabase::Schema;
1060 extends 'DBIx::Class::Schema';
1062 around connection => sub {
1063 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1065 my $postfix = delete $attr->{schema_name_postfix};
1070 $self->append_db_name($postfix);
1074 sub append_db_name {
1075 my ( $self, $postfix ) = @_;
1079 { $_->name =~ /^\w+\./mx }
1081 { $self->source($_) }
1084 foreach my $source (@sources_with_db) {
1085 my $name = $source->name;
1086 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1088 $source->name($name);
1094 By overridding the L<connection|DBIx::Class::Schama/connection>
1095 method and extracting a custom option from the provided \%attr hashref one can
1096 then simply iterate over all the Schema's ResultSources, renaming them as
1099 To use this facility, simply add or modify the \%attr hashref that is passed to
1100 L<connection|DBIx::Class::Schama/connect>, as follows:
1103 = MyDatabase::Schema->connect(
1108 schema_name_postfix => '_dev'
1109 # ... Other options as desired ...
1112 Obviously, one could accomplish even more advanced mapping via a hash map or a
1117 As of version 0.04001, there is improved transaction support in
1118 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1119 example of the recommended way to use it:
1121 my $genus = $schema->resultset('Genus')->find(12);
1123 my $coderef2 = sub {
1128 my $coderef1 = sub {
1129 $genus->add_to_species({ name => 'troglodyte' });
1132 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1133 return $genus->species;
1138 $rs = $schema->txn_do($coderef1);
1141 if ($@) { # Transaction failed
1142 die "the sky is falling!" #
1143 if ($@ =~ /Rollback failed/); # Rollback failed
1145 deal_with_failed_transaction();
1148 Nested transactions will work as expected. That is, only the outermost
1149 transaction will actually issue a commit to the $dbh, and a rollback
1150 at any level of any transaction will cause the entire nested
1151 transaction to fail. Support for savepoints and for true nested
1152 transactions (for databases that support them) will hopefully be added
1157 =head2 Creating Schemas From An Existing Database
1159 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1160 L<DBIx::Class::Schema> and associated sources by examining the database.
1162 The recommend way of achieving this is to use the
1163 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1165 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1166 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1168 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1169 source definitions for all the tables found in the C<foo> database.
1171 =head2 Creating DDL SQL
1173 The following functionality requires you to have L<SQL::Translator>
1174 (also known as "SQL Fairy") installed.
1176 To create a set of database-specific .sql files for the above schema:
1178 my $schema = My::Schema->connect($dsn);
1179 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1184 By default this will create schema files in the current directory, for
1185 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1187 To create a new database using the schema:
1189 my $schema = My::Schema->connect($dsn);
1190 $schema->deploy({ add_drop_tables => 1});
1192 To import created .sql files using the mysql client:
1194 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1196 To create C<ALTER TABLE> conversion scripts to update a database to a
1197 newer version of your schema at a later point, first set a new
1198 C<$VERSION> in your Schema file, then:
1200 my $schema = My::Schema->connect($dsn);
1201 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1207 This will produce new database-specific .sql files for the new version
1208 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1209 requires that the files for 0.1 as created above are available in the
1210 given directory to diff against.
1212 =head2 Select from dual
1214 Dummy tables are needed by some databases to allow calling functions
1215 or expressions that aren't based on table content, for examples of how
1216 this applies to various database types, see:
1217 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1219 Note: If you're using Oracles dual table don't B<ever> do anything
1220 other than a select, if you CRUD on your dual table you *will* break
1223 Make a table class as you would for any other table
1225 package MyAppDB::Dual;
1228 use base 'DBIx::Class';
1229 __PACKAGE__->load_components("Core");
1230 __PACKAGE__->table("Dual");
1231 __PACKAGE__->add_columns(
1233 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1236 Once you've loaded your table class select from it using C<select>
1237 and C<as> instead of C<columns>
1239 my $rs = $schema->resultset('Dual')->search(undef,
1240 { select => [ 'sydate' ],
1245 All you have to do now is be careful how you access your resultset, the below
1246 will not work because there is no column called 'now' in the Dual table class
1248 while (my $dual = $rs->next) {
1249 print $dual->now."\n";
1251 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1253 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1254 your Dual class for whatever you wanted to select from dual, but that's just
1255 silly, instead use C<get_column>
1257 while (my $dual = $rs->next) {
1258 print $dual->get_column('now')."\n";
1263 my $cursor = $rs->cursor;
1264 while (my @vals = $cursor->next) {
1265 print $vals[0]."\n";
1268 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1269 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1270 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1271 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1272 L<SQL::Translator> to not create table dual:
1275 add_drop_table => 1,
1276 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1278 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1280 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1282 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1283 while ( my $dual = $rs->next ) {
1284 print $dual->{now}."\n";
1287 Here are some example C<select> conditions to illustrate the different syntax
1288 you could use for doing stuff like
1289 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1291 # get a sequence value
1292 select => [ 'A_SEQ.nextval' ],
1294 # get create table sql
1295 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1297 # get a random num between 0 and 100
1298 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1301 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1304 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1306 # which day of the week were you born on?
1307 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1309 # select 16 rows from dual
1310 select => [ "'hello'" ],
1312 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1316 =head2 Adding Indexes And Functions To Your SQL
1318 Often you will want indexes on columns on your table to speed up searching. To
1319 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1320 class (refer to the advanced
1321 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1322 to share a hook between multiple sources):
1324 package My::Schema::Result::Artist;
1326 __PACKAGE__->table('artist');
1327 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1329 sub sqlt_deploy_hook {
1330 my ($self, $sqlt_table) = @_;
1332 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1337 Sometimes you might want to change the index depending on the type of the
1338 database for which SQL is being generated:
1340 my ($db_type = $sqlt_table->schema->translator->producer_type)
1341 =~ s/^SQL::Translator::Producer:://;
1343 You can also add hooks to the schema level to stop certain tables being
1350 sub sqlt_deploy_hook {
1351 my ($self, $sqlt_schema) = @_;
1353 $sqlt_schema->drop_table('table_name');
1356 You could also add views, procedures or triggers to the output using
1357 L<SQL::Translator::Schema/add_view>,
1358 L<SQL::Translator::Schema/add_procedure> or
1359 L<SQL::Translator::Schema/add_trigger>.
1362 =head2 Schema versioning
1364 The following example shows simplistically how you might use DBIx::Class to
1365 deploy versioned schemas to your customers. The basic process is as follows:
1371 Create a DBIx::Class schema
1383 Modify schema to change functionality
1387 Deploy update to customers
1391 B<Create a DBIx::Class schema>
1393 This can either be done manually, or generated from an existing database as
1394 described under L</Creating Schemas From An Existing Database>
1398 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1400 B<Deploy to customers>
1402 There are several ways you could deploy your schema. These are probably
1403 beyond the scope of this recipe, but might include:
1409 Require customer to apply manually using their RDBMS.
1413 Package along with your app, making database dump/schema update/tests
1414 all part of your install.
1418 B<Modify the schema to change functionality>
1420 As your application evolves, it may be necessary to modify your schema
1421 to change functionality. Once the changes are made to your schema in
1422 DBIx::Class, export the modified schema and the conversion scripts as
1423 in L</Creating DDL SQL>.
1425 B<Deploy update to customers>
1427 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1428 Schema class. This will add a new table to your database called
1429 C<dbix_class_schema_vesion> which will keep track of which version is installed
1430 and warn if the user trys to run a newer schema version than the
1431 database thinks it has.
1433 Alternatively, you can send the conversion sql scripts to your
1436 =head2 Setting quoting for the generated SQL.
1438 If the database contains column names with spaces and/or reserved words, they
1439 need to be quoted in the SQL queries. This is done using:
1441 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1442 __PACKAGE__->storage->sql_maker->name_sep('.');
1444 The first sets the quote characters. Either a pair of matching
1445 brackets, or a C<"> or C<'>:
1447 __PACKAGE__->storage->sql_maker->quote_char('"');
1449 Check the documentation of your database for the correct quote
1450 characters to use. C<name_sep> needs to be set to allow the SQL
1451 generator to put the quotes the correct place.
1453 In most cases you should set these as part of the arguments passed to
1454 L<DBIx::Class::Schema/connect>:
1456 my $schema = My::Schema->connect(
1466 =head2 Setting limit dialect for SQL::Abstract::Limit
1468 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1469 the remote SQL server by looking at the database handle. This is a
1470 common problem when using the DBD::JDBC, since the DBD-driver only
1471 know that in has a Java-driver available, not which JDBC driver the
1472 Java component has loaded. This specifically sets the limit_dialect
1473 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1476 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1478 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1479 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1481 The limit dialect can also be set at connect time by specifying a
1482 C<limit_dialect> key in the final hash as shown above.
1484 =head2 Working with PostgreSQL array types
1486 You can also assign values to PostgreSQL array columns by passing array
1487 references in the C<\%columns> (C<\%vals>) hashref of the
1488 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1491 $resultset->create({
1492 numbers => [1, 2, 3]
1497 numbers => [1, 2, 3]
1504 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1505 methods) you cannot directly use array references (since this is interpreted as
1506 a list of values to be C<OR>ed), but you can use the following syntax to force
1507 passing them as bind values:
1511 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1515 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1516 placeholders and bind values (subqueries)> for more explanation. Note that
1517 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1518 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1519 arrayrefs together with the column name, like this: C<< [column_name => value]
1522 =head1 BOOTSTRAPPING/MIGRATING
1524 =head2 Easy migration from class-based to schema-based setup
1526 You want to start using the schema-based approach to L<DBIx::Class>
1527 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1528 of existing classes that you don't want to move by hand. Try this nifty script
1532 use SQL::Translator;
1534 my $schema = MyDB->schema_instance;
1536 my $translator = SQL::Translator->new(
1537 debug => $debug || 0,
1538 trace => $trace || 0,
1539 no_comments => $no_comments || 0,
1540 show_warnings => $show_warnings || 0,
1541 add_drop_table => $add_drop_table || 0,
1542 validate => $validate || 0,
1544 'DBIx::Schema' => $schema,
1547 'prefix' => 'My::Schema',
1551 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1552 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1554 my $output = $translator->translate(@args) or die
1555 "Error: " . $translator->error;
1559 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1560 namespace, which is currently left as an exercise for the reader.
1562 =head1 OVERLOADING METHODS
1564 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1565 method calls, useful for things like default values and triggers. You have to
1566 use calls to C<next::method> to overload methods. More information on using
1567 L<Class::C3> with L<DBIx::Class> can be found in
1568 L<DBIx::Class::Manual::Component>.
1570 =head2 Setting default values for a row
1572 It's as simple as overriding the C<new> method. Note the use of
1576 my ( $class, $attrs ) = @_;
1578 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1580 my $new = $class->next::method($attrs);
1585 For more information about C<next::method>, look in the L<Class::C3>
1586 documentation. See also L<DBIx::Class::Manual::Component> for more
1587 ways to write your own base classes to do this.
1589 People looking for ways to do "triggers" with DBIx::Class are probably
1590 just looking for this.
1592 =head2 Changing one field whenever another changes
1594 For example, say that you have three columns, C<id>, C<number>, and
1595 C<squared>. You would like to make changes to C<number> and have
1596 C<squared> be automagically set to the value of C<number> squared.
1597 You can accomplish this by overriding C<store_column>:
1600 my ( $self, $name, $value ) = @_;
1601 if ($name eq 'number') {
1602 $self->squared($value * $value);
1604 $self->next::method($name, $value);
1607 Note that the hard work is done by the call to C<next::method>, which
1608 redispatches your call to store_column in the superclass(es).
1610 =head2 Automatically creating related objects
1612 You might have a class C<Artist> which has many C<CD>s. Further, if you
1613 want to create a C<CD> object every time you insert an C<Artist> object.
1614 You can accomplish this by overriding C<insert> on your objects:
1617 my ( $self, @args ) = @_;
1618 $self->next::method(@args);
1619 $self->cds->new({})->fill_from_artist($self)->insert;
1623 where C<fill_from_artist> is a method you specify in C<CD> which sets
1624 values in C<CD> based on the data in the C<Artist> object you pass in.
1626 =head2 Wrapping/overloading a column accessor
1630 Say you have a table "Camera" and want to associate a description
1631 with each camera. For most cameras, you'll be able to generate the description from
1632 the other columns. However, in a few special cases you may want to associate a
1633 custom description with a camera.
1637 In your database schema, define a description field in the "Camera" table that
1638 can contain text and null values.
1640 In DBIC, we'll overload the column accessor to provide a sane default if no
1641 custom description is defined. The accessor will either return or generate the
1642 description, depending on whether the field is null or not.
1644 First, in your "Camera" schema class, define the description field as follows:
1646 __PACKAGE__->add_columns(description => { accessor => '_description' });
1648 Next, we'll define the accessor-wrapper subroutine:
1653 # If there is an update to the column, we'll let the original accessor
1655 return $self->_description(@_) if @_;
1657 # Fetch the column value.
1658 my $description = $self->_description;
1660 # If there's something in the description field, then just return that.
1661 return $description if defined $description && length $descripton;
1663 # Otherwise, generate a description.
1664 return $self->generate_description;
1667 =head1 DEBUGGING AND PROFILING
1669 =head2 DBIx::Class objects with Data::Dumper
1671 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1672 be hard to find the pertinent data in all the data it can generate.
1673 Specifically, if one naively tries to use it like so,
1677 my $cd = $schema->resultset('CD')->find(1);
1680 several pages worth of data from the CD object's schema and result source will
1681 be dumped to the screen. Since usually one is only interested in a few column
1682 values of the object, this is not very helpful.
1684 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1685 it. Simply define a hook that L<Data::Dumper> will call on the object before
1686 dumping it. For example,
1693 result_source => undef,
1701 local $Data::Dumper::Freezer = '_dumper_hook';
1703 my $cd = $schema->resultset('CD')->find(1);
1705 # dumps $cd without its ResultSource
1707 If the structure of your schema is such that there is a common base class for
1708 all your table classes, simply put a method similar to C<_dumper_hook> in the
1709 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1710 will automagically clean up your data before printing it. See
1711 L<Data::Dumper/EXAMPLES> for more information.
1715 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1716 executed as well as notifications of query completion and transaction
1717 begin/commit. If you'd like to profile the SQL you can subclass the
1718 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1721 package My::Profiler;
1724 use base 'DBIx::Class::Storage::Statistics';
1726 use Time::HiRes qw(time);
1735 $self->print("Executing $sql: ".join(', ', @params)."\n");
1744 my $elapsed = sprintf("%0.4f", time() - $start);
1745 $self->print("Execution took $elapsed seconds.\n");
1751 You can then install that class as the debugging object:
1753 __PACKAGE__->storage->debugobj(new My::Profiler());
1754 __PACKAGE__->storage->debug(1);
1756 A more complicated example might involve storing each execution of SQL in an
1764 my $elapsed = time() - $start;
1765 push(@{ $calls{$sql} }, {
1771 You could then create average, high and low execution times for an SQL
1772 statement and dig down to see if certain parameters cause aberrant behavior.
1773 You might want to check out L<DBIx::Class::QueryLog> as well.
1775 =head1 STARTUP SPEED
1777 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1778 as the ORM loads all the relevant classes. This section examines
1779 techniques for reducing the startup delay.
1781 These tips are are listed in order of decreasing effectiveness - so the
1782 first tip, if applicable, should have the greatest effect on your
1785 =head2 Statically Define Your Schema
1788 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1789 classes dynamically based on the database schema then there will be a
1790 significant startup delay.
1792 For production use a statically defined schema (which can be generated
1793 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1794 the database schema once - see
1795 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1796 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1797 details on creating static schemas from a database).
1799 =head2 Move Common Startup into a Base Class
1801 Typically L<DBIx::Class> result classes start off with
1803 use base qw/DBIx::Class/;
1804 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1806 If this preamble is moved into a common base class:-
1810 use base qw/DBIx::Class/;
1811 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1814 and each result class then uses this as a base:-
1816 use base qw/MyDBICbase/;
1818 then the load_components is only performed once, which can result in a
1819 considerable startup speedup for schemas with many classes.
1821 =head2 Explicitly List Schema Result Classes
1823 The schema class will normally contain
1825 __PACKAGE__->load_classes();
1827 to load the result classes. This will use L<Module::Find|Module::Find>
1828 to find and load the appropriate modules. Explicitly defining the
1829 classes you wish to load will remove the overhead of
1830 L<Module::Find|Module::Find> and the related directory operations:-
1832 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1834 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1835 syntax to load the appropriate classes there is not a direct alternative
1836 avoiding L<Module::Find|Module::Find>.
1840 =head2 Cached statements
1842 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1843 This is normally a good idea, but if too many statements are cached, the database may use too much
1844 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1845 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1847 # print all currently cached prepared statements
1848 print for keys %{$schema->storage->dbh->{CachedKids}};
1849 # get a count of currently cached prepared statements
1850 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1852 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1855 my $kids = $schema->storage->dbh->{CachedKids};
1856 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1858 But what you probably want is to expire unused statements and not those that are used frequently.
1859 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1863 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1864 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },