3 DBIx::Class::Manual::Cookbook - Miscellaneous recipes
9 When you expect a large number of results, you can ask L<DBIx::Class> for a
10 paged resultset, which will fetch only a defined number of records at a time:
12 my $rs = $schema->resultset('Artist')->search(
15 page => 1, # page to return (defaults to 1)
16 rows => 10, # number of results per page
20 return $rs->all(); # all records for page 1
22 You can get a L<Data::Page> object for the resultset (suitable for use
23 in e.g. a template) using the C<pager> method:
27 =head2 Complex WHERE clauses
29 Sometimes you need to formulate a query using specific operators:
31 my @albums = $schema->resultset('Album')->search({
32 artist => { 'like', '%Lamb%' },
33 title => { 'like', '%Fear of Fours%' },
36 This results in something like the following C<WHERE> clause:
38 WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
40 Other queries might require slightly more complex logic:
42 my @albums = $schema->resultset('Album')->search({
45 artist => { 'like', '%Smashing Pumpkins%' },
46 title => 'Siamese Dream',
48 artist => 'Starchildren',
52 This results in the following C<WHERE> clause:
54 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
55 OR artist = 'Starchildren'
57 For more information on generating complex queries, see
58 L<SQL::Abstract/WHERE CLAUSES>.
60 =head2 Retrieve one and only one row from a resultset
62 Sometimes you need only the first "top" row of a resultset. While this can be
63 easily done with L<< $rs->first|DBIx::Class::ResultSet/first >>, it is suboptimal,
64 as a full blown cursor for the resultset will be created and then immediately
65 destroyed after fetching the first row object.
66 L<< $rs->single|DBIx::Class::ResultSet/single >> is
67 designed specifically for this case - it will grab the first returned result
68 without even instantiating a cursor.
70 Before replacing all your calls to C<first()> with C<single()> please observe the
76 While single() takes a search condition just like search() does, it does
77 _not_ accept search attributes. However one can always chain a single() to
80 my $top_cd = $cd_rs -> search({}, { order_by => 'rating' }) -> single;
84 Since single() is the engine behind find(), it is designed to fetch a
85 single row per database query. Thus a warning will be issued when the
86 underlying SELECT returns more than one row. Sometimes however this usage
87 is valid: i.e. we have an arbitrary number of cd's but only one of them is
88 at the top of the charts at any given time. If you know what you are doing,
89 you can silence the warning by explicitly limiting the resultset size:
91 my $top_cd = $cd_rs -> search ({}, { order_by => 'rating', rows => 1 }) -> single;
95 =head2 Arbitrary SQL through a custom ResultSource
97 Sometimes you have to run arbitrary SQL because your query is too complex
98 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
99 be optimized for your database in a special way, but you still want to
100 get the results as a L<DBIx::Class::ResultSet>.
101 The recommended way to accomplish this is by defining a separate ResultSource
102 for your query. You can then inject complete SQL statements using a scalar
103 reference (this is a feature of L<SQL::Abstract>).
105 Say you want to run a complex custom query on your user data, here's what
106 you have to add to your User class:
108 package My::Schema::Result::User;
110 use base qw/DBIx::Class/;
112 # ->load_components, ->table, ->add_columns, etc.
114 # Make a new ResultSource based on the User class
115 my $source = __PACKAGE__->result_source_instance();
116 my $new_source = $source->new( $source );
117 $new_source->source_name( 'UserFriendsComplex' );
119 # Hand in your query as a scalar reference
120 # It will be added as a sub-select after FROM,
121 # so pay attention to the surrounding brackets!
122 $new_source->name( \<<SQL );
123 ( SELECT u.* FROM user u
124 INNER JOIN user_friends f ON u.id = f.user_id
125 WHERE f.friend_user_id = ?
127 SELECT u.* FROM user u
128 INNER JOIN user_friends f ON u.id = f.friend_user_id
129 WHERE f.user_id = ? )
132 # Finally, register your new ResultSource with your Schema
133 My::Schema->register_extra_source( 'UserFriendsComplex' => $new_source );
135 Next, you can execute your complex query using bind parameters like this:
137 my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {},
139 bind => [ 12345, 12345 ]
143 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
144 that you cannot modify the rows it contains, ie. cannot call L</update>,
145 L</delete>, ... on it).
147 If you prefer to have the definitions of these custom ResultSources in separate
148 files (instead of stuffing all of them into the same resultset class), you can
149 achieve the same with subclassing the resultset class and defining the
152 package My::Schema::Result::UserFriendsComplex;
154 use My::Schema::Result::User;
155 use base qw/My::Schema::Result::User/;
157 __PACKAGE__->table('dummy'); # currently must be called before anything else
159 # Hand in your query as a scalar reference
160 # It will be added as a sub-select after FROM,
161 # so pay attention to the surrounding brackets!
162 __PACKAGE__->name( \<<SQL );
163 ( SELECT u.* FROM user u
164 INNER JOIN user_friends f ON u.id = f.user_id
165 WHERE f.friend_user_id = ?
167 SELECT u.* FROM user u
168 INNER JOIN user_friends f ON u.id = f.friend_user_id
169 WHERE f.user_id = ? )
174 =head2 Using specific columns
176 When you only want specific columns from a table, you can use
177 C<columns> to specify which ones you need. This is useful to avoid
178 loading columns with large amounts of data that you aren't about to
181 my $rs = $schema->resultset('Artist')->search(
184 columns => [qw/ name /]
189 # SELECT artist.name FROM artist
191 This is a shortcut for C<select> and C<as>, see below. C<columns>
192 cannot be used together with C<select> and C<as>.
194 =head2 Using database functions or stored procedures
196 The combination of C<select> and C<as> can be used to return the result of a
197 database function or stored procedure as a column value. You use C<select> to
198 specify the source for your column value (e.g. a column name, function, or
199 stored procedure name). You then use C<as> to set the column name you will use
200 to access the returned value:
202 my $rs = $schema->resultset('Artist')->search(
205 select => [ 'name', { LENGTH => 'name' } ],
206 as => [qw/ name name_length /],
211 # SELECT name name, LENGTH( name )
214 Note that the C< as > attribute has absolutely nothing to with the sql
215 syntax C< SELECT foo AS bar > (see the documentation in
216 L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
217 column in your base class (i.e. it was added with C<add_columns>), you
218 just access it as normal. Our C<Artist> class has a C<name> column, so
219 we just use the C<name> accessor:
221 my $artist = $rs->first();
222 my $name = $artist->name();
224 If on the other hand the alias does not correspond to an existing column, you
225 have to fetch the value using the C<get_column> accessor:
227 my $name_length = $artist->get_column('name_length');
229 If you don't like using C<get_column>, you can always create an accessor for
230 any of your aliases using either of these:
232 # Define accessor manually:
233 sub name_length { shift->get_column('name_length'); }
235 # Or use DBIx::Class::AccessorGroup:
236 __PACKAGE__->mk_group_accessors('column' => 'name_length');
238 =head2 SELECT DISTINCT with multiple columns
240 my $rs = $schema->resultset('Artist')->search(
243 columns => [ qw/artistid name rank/ ],
248 my $rs = $schema->resultset('Artist')->search(
251 columns => [ qw/artistid name rank/ ],
252 group_by => [ qw/artistid name rank/ ],
257 # SELECT me.artistid, me.name, me.rank
259 # GROUP BY artistid, name, rank
261 =head2 SELECT COUNT(DISTINCT colname)
263 my $rs = $schema->resultset('Artist')->search(
266 columns => [ qw/name/ ],
271 my $rs = $schema->resultset('Artist')->search(
274 columns => [ qw/name/ ],
275 group_by => [ qw/name/ ],
279 my $count = $rs->count;
282 # SELECT COUNT( DISTINCT( me.name ) ) FROM artist me
284 =head2 Grouping results
286 L<DBIx::Class> supports C<GROUP BY> as follows:
288 my $rs = $schema->resultset('Artist')->search(
292 select => [ 'name', { count => 'cds.id' } ],
293 as => [qw/ name cd_count /],
294 group_by => [qw/ name /]
299 # SELECT name, COUNT( cd.id ) FROM artist
300 # LEFT JOIN cd ON artist.id = cd.artist
303 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
304 are in any way unsure about the use of the attributes above (C< join
305 >, C< select >, C< as > and C< group_by >).
307 =head2 Subqueries (EXPERIMENTAL)
309 You can write subqueries relatively easily in DBIC.
311 my $inside_rs = $schema->resultset('Artist')->search({
312 name => [ 'Billy Joel', 'Brittany Spears' ],
315 my $rs = $schema->resultset('CD')->search({
316 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
319 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
321 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
322 The following will B<not> work:
324 my $rs = $schema->resultset('CD')->search({
325 artist_id => $inside_rs->get_column('id')->as_query,
330 Subqueries are supported in the where clause (first hashref), and in the
331 from, select, and +select attributes.
333 =head3 Correlated subqueries
335 my $cdrs = $schema->resultset('CD');
336 my $rs = $cdrs->search({
338 '=' => $cdrs->search(
339 { artistid => { '=' => \'me.artistid' } },
341 )->get_column('year')->max_rs->as_query,
345 That creates the following SQL:
347 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
350 SELECT MAX(inner.year)
352 WHERE artistid = me.artistid
357 Please note that subqueries are considered an experimental feature.
359 =head2 Predefined searches
361 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
362 and define often used searches as methods:
364 package My::DBIC::ResultSet::CD;
367 use base 'DBIx::Class::ResultSet';
369 sub search_cds_ordered {
372 return $self->search(
374 { order_by => 'name DESC' },
380 To use your resultset, first tell DBIx::Class to create an instance of it
381 for you, in your My::DBIC::Schema::CD class:
383 # class definition as normal
384 __PACKAGE__->load_components(qw/ Core /);
385 __PACKAGE__->table('cd');
387 # tell DBIC to use the custom ResultSet class
388 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
390 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
392 Then call your new method in your code:
394 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
396 =head2 Using SQL functions on the left hand side of a comparison
398 Using SQL functions on the left hand side of a comparison is generally
399 not a good idea since it requires a scan of the entire table. However,
400 it can be accomplished with C<DBIx::Class> when necessary.
402 If you do not have quoting on, simply include the function in your search
403 specification as you would any column:
405 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
407 With quoting on, or for a more portable solution, use the C<where>
410 $rs->search({}, { where => \'YEAR(date_of_birth) = 1979' });
414 (When the bind args ordering bug is fixed, this technique will be better
415 and can replace the one above.)
417 With quoting on, or for a more portable solution, use the C<where> and
421 where => \'YEAR(date_of_birth) = ?',
427 =head1 JOINS AND PREFETCHING
429 =head2 Using joins and prefetch
431 You can use the C<join> attribute to allow searching on, or sorting your
432 results by, one or more columns in a related table. To return all CDs matching
433 a particular artist name:
435 my $rs = $schema->resultset('CD')->search(
437 'artist.name' => 'Bob Marley'
440 join => 'artist', # join the artist table
445 # SELECT cd.* FROM cd
446 # JOIN artist ON cd.artist = artist.id
447 # WHERE artist.name = 'Bob Marley'
449 If required, you can now sort on any column in the related tables by including
450 it in your C<order_by> attribute:
452 my $rs = $schema->resultset('CD')->search(
454 'artist.name' => 'Bob Marley'
458 order_by => [qw/ artist.name /]
463 # SELECT cd.* FROM cd
464 # JOIN artist ON cd.artist = artist.id
465 # WHERE artist.name = 'Bob Marley'
466 # ORDER BY artist.name
468 Note that the C<join> attribute should only be used when you need to search or
469 sort using columns in a related table. Joining related tables when you only
470 need columns from the main table will make performance worse!
472 Now let's say you want to display a list of CDs, each with the name of the
473 artist. The following will work fine:
475 while (my $cd = $rs->next) {
476 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
479 There is a problem however. We have searched both the C<cd> and C<artist> tables
480 in our main query, but we have only returned data from the C<cd> table. To get
481 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
484 SELECT artist.* FROM artist WHERE artist.id = ?
486 A statement like the one above will run for each and every CD returned by our
487 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
490 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
491 This allows you to fetch results from related tables in advance:
493 my $rs = $schema->resultset('CD')->search(
495 'artist.name' => 'Bob Marley'
499 order_by => [qw/ artist.name /],
500 prefetch => 'artist' # return artist data too!
504 # Equivalent SQL (note SELECT from both "cd" and "artist"):
505 # SELECT cd.*, artist.* FROM cd
506 # JOIN artist ON cd.artist = artist.id
507 # WHERE artist.name = 'Bob Marley'
508 # ORDER BY artist.name
510 The code to print the CD list remains the same:
512 while (my $cd = $rs->next) {
513 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
516 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
517 so no additional SQL statements are executed. You now have a much more
520 Note that as of L<DBIx::Class> 0.05999_01, C<prefetch> I<can> be used with
521 C<has_many> relationships.
523 Also note that C<prefetch> should only be used when you know you will
524 definitely use data from a related table. Pre-fetching related tables when you
525 only need columns from the main table will make performance worse!
527 =head2 Multiple joins
529 In the examples above, the C<join> attribute was a scalar. If you
530 pass an array reference instead, you can join to multiple tables. In
531 this example, we want to limit the search further, using
534 # Relationships defined elsewhere:
535 # CD->belongs_to('artist' => 'Artist');
536 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
537 my $rs = $schema->resultset('CD')->search(
539 'artist.name' => 'Bob Marley'
540 'liner_notes.notes' => { 'like', '%some text%' },
543 join => [qw/ artist liner_notes /],
544 order_by => [qw/ artist.name /],
549 # SELECT cd.*, artist.*, liner_notes.* FROM cd
550 # JOIN artist ON cd.artist = artist.id
551 # JOIN liner_notes ON cd.id = liner_notes.cd
552 # WHERE artist.name = 'Bob Marley'
553 # ORDER BY artist.name
555 =head2 Multi-step joins
557 Sometimes you want to join more than one relationship deep. In this example,
558 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
559 contain a specific string:
561 # Relationships defined elsewhere:
562 # Artist->has_many('cds' => 'CD', 'artist');
563 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
565 my $rs = $schema->resultset('Artist')->search(
567 'liner_notes.notes' => { 'like', '%some text%' },
571 'cds' => 'liner_notes'
577 # SELECT artist.* FROM artist
578 # LEFT JOIN cd ON artist.id = cd.artist
579 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
580 # WHERE liner_notes.notes LIKE '%some text%'
582 Joins can be nested to an arbitrary level. So if we decide later that we
583 want to reduce the number of Artists returned based on who wrote the liner
586 # Relationship defined elsewhere:
587 # LinerNotes->belongs_to('author' => 'Person');
589 my $rs = $schema->resultset('Artist')->search(
591 'liner_notes.notes' => { 'like', '%some text%' },
592 'author.name' => 'A. Writer'
597 'liner_notes' => 'author'
604 # SELECT artist.* FROM artist
605 # LEFT JOIN cd ON artist.id = cd.artist
606 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
607 # LEFT JOIN author ON author.id = liner_notes.author
608 # WHERE liner_notes.notes LIKE '%some text%'
609 # AND author.name = 'A. Writer'
611 =head2 Multi-step and multiple joins
613 With various combinations of array and hash references, you can join
614 tables in any combination you desire. For example, to join Artist to
615 CD and Concert, and join CD to LinerNotes:
617 # Relationships defined elsewhere:
618 # Artist->has_many('concerts' => 'Concert', 'artist');
620 my $rs = $schema->resultset('Artist')->search(
633 # SELECT artist.* FROM artist
634 # LEFT JOIN cd ON artist.id = cd.artist
635 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
636 # LEFT JOIN concert ON artist.id = concert.artist
638 =head2 Multi-step prefetch
640 From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
641 deep using the same syntax as a multi-step join:
643 my $rs = $schema->resultset('Tag')->search(
653 # SELECT tag.*, cd.*, artist.* FROM tag
654 # JOIN cd ON tag.cd = cd.id
655 # JOIN artist ON cd.artist = artist.id
657 Now accessing our C<cd> and C<artist> relationships does not need additional
660 my $tag = $rs->first;
661 print $tag->cd->artist->name;
663 =head1 ROW-LEVEL OPERATIONS
665 =head2 Retrieving a row object's Schema
667 It is possible to get a Schema object from a row object like so:
669 my $schema = $cd->result_source->schema;
670 # use the schema as normal:
671 my $artist_rs = $schema->resultset('Artist');
673 This can be useful when you don't want to pass around a Schema object to every
676 =head2 Getting the value of the primary key for the last database insert
678 AKA getting last_insert_id
680 If you are using PK::Auto (which is a core component as of 0.07), this is
683 my $foo = $rs->create(\%blah);
685 my $id = $foo->id; # foo->my_primary_key_field will also work.
687 If you are not using autoincrementing primary keys, this will probably
688 not work, but then you already know the value of the last primary key anyway.
690 =head2 Stringification
692 Employ the standard stringification technique by using the C<overload>
695 To make an object stringify itself as a single column, use something
696 like this (replace C<name> with the column/method of your choice):
698 use overload '""' => sub { shift->name}, fallback => 1;
700 For more complex stringification, you can use an anonymous subroutine:
702 use overload '""' => sub { $_[0]->name . ", " .
703 $_[0]->address }, fallback => 1;
705 =head3 Stringification Example
707 Suppose we have two tables: C<Product> and C<Category>. The table
710 Product(id, Description, category)
711 Category(id, Description)
713 C<category> is a foreign key into the Category table.
715 If you have a Product object C<$obj> and write something like
719 things will not work as expected.
721 To obtain, for example, the category description, you should add this
722 method to the class defining the Category table:
724 use overload "" => sub {
727 return $self->Description;
730 =head2 Want to know if find_or_create found or created a row?
732 Just use C<find_or_new> instead, then check C<in_storage>:
734 my $obj = $rs->find_or_new({ blah => 'blarg' });
735 unless ($obj->in_storage) {
737 # do whatever else you wanted if it was a new row
740 =head2 Dynamic Sub-classing DBIx::Class proxy classes
742 AKA multi-class object inflation from one table
744 L<DBIx::Class> classes are proxy classes, therefore some different
745 techniques need to be employed for more than basic subclassing. In
746 this example we have a single user table that carries a boolean bit
747 for admin. We would like like to give the admin users
748 objects(L<DBIx::Class::Row>) the same methods as a regular user but
749 also special admin only methods. It doesn't make sense to create two
750 seperate proxy-class files for this. We would be copying all the user
751 methods into the Admin class. There is a cleaner way to accomplish
754 Overriding the C<inflate_result> method within the User proxy-class
755 gives us the effect we want. This method is called by
756 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
757 grab the object being returned, inspect the values we are looking for,
758 bless it if it's an admin object, and then return it. See the example
765 use base qw/DBIx::Class::Schema/;
767 __PACKAGE__->load_namespaces;
770 B<Proxy-Class definitions>
772 package My::Schema::Result::User;
776 use base qw/DBIx::Class/;
778 ### Defined what our admin class is for ensure_class_loaded
779 my $admin_class = __PACKAGE__ . '::Admin';
781 __PACKAGE__->load_components(qw/Core/);
783 __PACKAGE__->table('users');
785 __PACKAGE__->add_columns(qw/user_id email password
786 firstname lastname active
789 __PACKAGE__->set_primary_key('user_id');
793 my $ret = $self->next::method(@_);
794 if( $ret->admin ) {### If this is an admin rebless for extra functions
795 $self->ensure_class_loaded( $admin_class );
796 bless $ret, $admin_class;
802 print "I am a regular user.\n";
807 package My::Schema::Result::User::Admin;
811 use base qw/My::Schema::Result::User/;
815 print "I am an admin.\n";
821 print "I am doing admin stuff\n";
831 my $user_data = { email => 'someguy@place.com',
835 my $admin_data = { email => 'someadmin@adminplace.com',
839 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
841 $schema->resultset('User')->create( $user_data );
842 $schema->resultset('User')->create( $admin_data );
844 ### Now we search for them
845 my $user = $schema->resultset('User')->single( $user_data );
846 my $admin = $schema->resultset('User')->single( $admin_data );
848 print ref $user, "\n";
849 print ref $admin, "\n";
851 print $user->password , "\n"; # pass1
852 print $admin->password , "\n";# pass2; inherited from User
853 print $user->hello , "\n";# I am a regular user.
854 print $admin->hello, "\n";# I am an admin.
856 ### The statement below will NOT print
857 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
858 ### The statement below will print
859 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
861 =head2 Skip row object creation for faster results
863 DBIx::Class is not built for speed, it's built for convenience and
864 ease of use, but sometimes you just need to get the data, and skip the
867 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
869 my $rs = $schema->resultset('CD');
871 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
873 my $hash_ref = $rs->find(1);
877 Beware, changing the Result class using
878 L<DBIx::Class::ResultSet/result_class> will replace any existing class
879 completely including any special components loaded using
880 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
882 =head2 Get raw data for blindingly fast results
884 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
885 above is not fast enough for you, you can use a DBIx::Class to return values
886 exactly as they come out of the database with none of the convenience methods
889 This is used like so:
891 my $cursor = $rs->cursor
892 while (my @vals = $cursor->next) {
893 # use $val[0..n] here
896 You will need to map the array offsets to particular columns (you can
897 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
899 =head1 RESULTSET OPERATIONS
901 =head2 Getting Schema from a ResultSet
903 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
905 $rs->result_source->schema
907 =head2 Getting Columns Of Data
911 If you want to find the sum of a particular column there are several
912 ways, the obvious one is to use search:
914 my $rs = $schema->resultset('Items')->search(
917 select => [ { sum => 'Cost' } ],
918 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
921 my $tc = $rs->first->get_column('total_cost');
923 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
924 returned when you ask the C<ResultSet> for a column using
927 my $cost = $schema->resultset('Items')->get_column('Cost');
930 With this you can also do:
932 my $minvalue = $cost->min;
933 my $maxvalue = $cost->max;
935 Or just iterate through the values of this column only:
937 while ( my $c = $cost->next ) {
941 foreach my $c ($cost->all) {
945 C<ResultSetColumn> only has a limited number of built-in functions, if
946 you need one that it doesn't have, then you can use the C<func> method
949 my $avg = $cost->func('AVERAGE');
951 This will cause the following SQL statement to be run:
953 SELECT AVERAGE(Cost) FROM Items me
955 Which will of course only work if your database supports this function.
956 See L<DBIx::Class::ResultSetColumn> for more documentation.
958 =head2 Creating a result set from a set of rows
960 Sometimes you have a (set of) row objects that you want to put into a
961 resultset without the need to hit the DB again. You can do that by using the
962 L<set_cache|DBIx::Class::Resultset/set_cache> method:
964 my @uploadable_groups;
965 while (my $group = $groups->next) {
966 if ($group->can_upload($self)) {
967 push @uploadable_groups, $group;
970 my $new_rs = $self->result_source->resultset;
971 $new_rs->set_cache(\@uploadable_groups);
975 =head1 USING RELATIONSHIPS
977 =head2 Create a new row in a related table
979 my $author = $book->create_related('author', { name => 'Fred'});
981 =head2 Search in a related table
983 Only searches for books named 'Titanic' by the author in $author.
985 my $books_rs = $author->search_related('books', { name => 'Titanic' });
987 =head2 Delete data in a related table
989 Deletes only the book named Titanic by the author in $author.
991 $author->delete_related('books', { name => 'Titanic' });
993 =head2 Ordering a relationship result set
995 If you always want a relation to be ordered, you can specify this when you
996 create the relationship.
998 To order C<< $book->pages >> by descending page_number, create the relation
1001 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
1003 =head2 Filtering a relationship result set
1005 If you want to get a filtered result set, you can just add add to $attr as follows:
1007 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1009 =head2 Many-to-many relationships
1011 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1014 use base 'DBIx::Class';
1015 __PACKAGE__->load_components('Core');
1016 __PACKAGE__->table('user');
1017 __PACKAGE__->add_columns(qw/id name/);
1018 __PACKAGE__->set_primary_key('id');
1019 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1020 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1022 package My::UserAddress;
1023 use base 'DBIx::Class';
1024 __PACKAGE__->load_components('Core');
1025 __PACKAGE__->table('user_address');
1026 __PACKAGE__->add_columns(qw/user address/);
1027 __PACKAGE__->set_primary_key(qw/user address/);
1028 __PACKAGE__->belongs_to('user' => 'My::User');
1029 __PACKAGE__->belongs_to('address' => 'My::Address');
1031 package My::Address;
1032 use base 'DBIx::Class';
1033 __PACKAGE__->load_components('Core');
1034 __PACKAGE__->table('address');
1035 __PACKAGE__->add_columns(qw/id street town area_code country/);
1036 __PACKAGE__->set_primary_key('id');
1037 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1038 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1040 $rs = $user->addresses(); # get all addresses for a user
1041 $rs = $address->users(); # get all users for an address
1043 =head2 Relationships across DB schemas
1045 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1046 is easy as long as the schemas themselves are all accessible via the same DBI
1047 connection. In most cases, this means that they are on the same database host
1048 as each other and your connecting database user has the proper permissions to them.
1050 To accomplish this one only needs to specify the DB schema name in the table
1051 declaration, like so...
1053 package MyDatabase::Main::Artist;
1054 use base qw/DBIx::Class/;
1055 __PACKAGE__->load_components(qw/PK::Auto Core/);
1057 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1059 __PACKAGE__->add_columns(qw/ artistid name /);
1060 __PACKAGE__->set_primary_key('artistid');
1061 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1065 Whatever string you specify there will be used to build the "FROM" clause in SQL
1068 The big drawback to this is you now have DB schema names hardcoded in your
1069 class files. This becomes especially troublesome if you have multiple instances
1070 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1071 the DB schemas are named based on the environment (e.g. database1_dev).
1073 However, one can dynamically "map" to the proper DB schema by overriding the
1074 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1075 building a renaming facility, like so:
1077 package MyDatabase::Schema;
1080 extends 'DBIx::Class::Schema';
1082 around connection => sub {
1083 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1085 my $postfix = delete $attr->{schema_name_postfix};
1090 $self->append_db_name($postfix);
1094 sub append_db_name {
1095 my ( $self, $postfix ) = @_;
1099 { $_->name =~ /^\w+\./mx }
1101 { $self->source($_) }
1104 foreach my $source (@sources_with_db) {
1105 my $name = $source->name;
1106 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1108 $source->name($name);
1114 By overridding the L<connection|DBIx::Class::Schama/connection>
1115 method and extracting a custom option from the provided \%attr hashref one can
1116 then simply iterate over all the Schema's ResultSources, renaming them as
1119 To use this facility, simply add or modify the \%attr hashref that is passed to
1120 L<connection|DBIx::Class::Schama/connect>, as follows:
1123 = MyDatabase::Schema->connect(
1128 schema_name_postfix => '_dev'
1129 # ... Other options as desired ...
1132 Obviously, one could accomplish even more advanced mapping via a hash map or a
1137 As of version 0.04001, there is improved transaction support in
1138 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1139 example of the recommended way to use it:
1141 my $genus = $schema->resultset('Genus')->find(12);
1143 my $coderef2 = sub {
1148 my $coderef1 = sub {
1149 $genus->add_to_species({ name => 'troglodyte' });
1152 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1153 return $genus->species;
1158 $rs = $schema->txn_do($coderef1);
1161 if ($@) { # Transaction failed
1162 die "the sky is falling!" #
1163 if ($@ =~ /Rollback failed/); # Rollback failed
1165 deal_with_failed_transaction();
1168 Nested transactions will work as expected. That is, only the outermost
1169 transaction will actually issue a commit to the $dbh, and a rollback
1170 at any level of any transaction will cause the entire nested
1171 transaction to fail. Support for savepoints and for true nested
1172 transactions (for databases that support them) will hopefully be added
1177 =head2 Creating Schemas From An Existing Database
1179 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1180 L<DBIx::Class::Schema> and associated sources by examining the database.
1182 The recommend way of achieving this is to use the
1183 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1185 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1186 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1188 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1189 source definitions for all the tables found in the C<foo> database.
1191 =head2 Creating DDL SQL
1193 The following functionality requires you to have L<SQL::Translator>
1194 (also known as "SQL Fairy") installed.
1196 To create a set of database-specific .sql files for the above schema:
1198 my $schema = My::Schema->connect($dsn);
1199 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1204 By default this will create schema files in the current directory, for
1205 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1207 To create a new database using the schema:
1209 my $schema = My::Schema->connect($dsn);
1210 $schema->deploy({ add_drop_tables => 1});
1212 To import created .sql files using the mysql client:
1214 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1216 To create C<ALTER TABLE> conversion scripts to update a database to a
1217 newer version of your schema at a later point, first set a new
1218 C<$VERSION> in your Schema file, then:
1220 my $schema = My::Schema->connect($dsn);
1221 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1227 This will produce new database-specific .sql files for the new version
1228 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1229 requires that the files for 0.1 as created above are available in the
1230 given directory to diff against.
1232 =head2 Select from dual
1234 Dummy tables are needed by some databases to allow calling functions
1235 or expressions that aren't based on table content, for examples of how
1236 this applies to various database types, see:
1237 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1239 Note: If you're using Oracles dual table don't B<ever> do anything
1240 other than a select, if you CRUD on your dual table you *will* break
1243 Make a table class as you would for any other table
1245 package MyAppDB::Dual;
1248 use base 'DBIx::Class';
1249 __PACKAGE__->load_components("Core");
1250 __PACKAGE__->table("Dual");
1251 __PACKAGE__->add_columns(
1253 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1256 Once you've loaded your table class select from it using C<select>
1257 and C<as> instead of C<columns>
1259 my $rs = $schema->resultset('Dual')->search(undef,
1260 { select => [ 'sydate' ],
1265 All you have to do now is be careful how you access your resultset, the below
1266 will not work because there is no column called 'now' in the Dual table class
1268 while (my $dual = $rs->next) {
1269 print $dual->now."\n";
1271 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1273 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1274 your Dual class for whatever you wanted to select from dual, but that's just
1275 silly, instead use C<get_column>
1277 while (my $dual = $rs->next) {
1278 print $dual->get_column('now')."\n";
1283 my $cursor = $rs->cursor;
1284 while (my @vals = $cursor->next) {
1285 print $vals[0]."\n";
1288 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1289 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1290 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1291 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1292 L<SQL::Translator> to not create table dual:
1295 add_drop_table => 1,
1296 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1298 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1300 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1302 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1303 while ( my $dual = $rs->next ) {
1304 print $dual->{now}."\n";
1307 Here are some example C<select> conditions to illustrate the different syntax
1308 you could use for doing stuff like
1309 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1311 # get a sequence value
1312 select => [ 'A_SEQ.nextval' ],
1314 # get create table sql
1315 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1317 # get a random num between 0 and 100
1318 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1321 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1324 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1326 # which day of the week were you born on?
1327 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1329 # select 16 rows from dual
1330 select => [ "'hello'" ],
1332 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1336 =head2 Adding Indexes And Functions To Your SQL
1338 Often you will want indexes on columns on your table to speed up searching. To
1339 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1340 class (refer to the advanced
1341 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1342 to share a hook between multiple sources):
1344 package My::Schema::Result::Artist;
1346 __PACKAGE__->table('artist');
1347 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1349 sub sqlt_deploy_hook {
1350 my ($self, $sqlt_table) = @_;
1352 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1357 Sometimes you might want to change the index depending on the type of the
1358 database for which SQL is being generated:
1360 my ($db_type = $sqlt_table->schema->translator->producer_type)
1361 =~ s/^SQL::Translator::Producer:://;
1363 You can also add hooks to the schema level to stop certain tables being
1370 sub sqlt_deploy_hook {
1371 my ($self, $sqlt_schema) = @_;
1373 $sqlt_schema->drop_table('table_name');
1376 You could also add views, procedures or triggers to the output using
1377 L<SQL::Translator::Schema/add_view>,
1378 L<SQL::Translator::Schema/add_procedure> or
1379 L<SQL::Translator::Schema/add_trigger>.
1382 =head2 Schema versioning
1384 The following example shows simplistically how you might use DBIx::Class to
1385 deploy versioned schemas to your customers. The basic process is as follows:
1391 Create a DBIx::Class schema
1403 Modify schema to change functionality
1407 Deploy update to customers
1411 B<Create a DBIx::Class schema>
1413 This can either be done manually, or generated from an existing database as
1414 described under L</Creating Schemas From An Existing Database>
1418 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1420 B<Deploy to customers>
1422 There are several ways you could deploy your schema. These are probably
1423 beyond the scope of this recipe, but might include:
1429 Require customer to apply manually using their RDBMS.
1433 Package along with your app, making database dump/schema update/tests
1434 all part of your install.
1438 B<Modify the schema to change functionality>
1440 As your application evolves, it may be necessary to modify your schema
1441 to change functionality. Once the changes are made to your schema in
1442 DBIx::Class, export the modified schema and the conversion scripts as
1443 in L</Creating DDL SQL>.
1445 B<Deploy update to customers>
1447 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1448 Schema class. This will add a new table to your database called
1449 C<dbix_class_schema_vesion> which will keep track of which version is installed
1450 and warn if the user trys to run a newer schema version than the
1451 database thinks it has.
1453 Alternatively, you can send the conversion sql scripts to your
1456 =head2 Setting quoting for the generated SQL.
1458 If the database contains column names with spaces and/or reserved words, they
1459 need to be quoted in the SQL queries. This is done using:
1461 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1462 __PACKAGE__->storage->sql_maker->name_sep('.');
1464 The first sets the quote characters. Either a pair of matching
1465 brackets, or a C<"> or C<'>:
1467 __PACKAGE__->storage->sql_maker->quote_char('"');
1469 Check the documentation of your database for the correct quote
1470 characters to use. C<name_sep> needs to be set to allow the SQL
1471 generator to put the quotes the correct place.
1473 In most cases you should set these as part of the arguments passed to
1474 L<DBIx::Class::Schema/connect>:
1476 my $schema = My::Schema->connect(
1486 =head2 Setting limit dialect for SQL::Abstract::Limit
1488 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1489 the remote SQL server by looking at the database handle. This is a
1490 common problem when using the DBD::JDBC, since the DBD-driver only
1491 know that in has a Java-driver available, not which JDBC driver the
1492 Java component has loaded. This specifically sets the limit_dialect
1493 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1496 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1498 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1499 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1501 The limit dialect can also be set at connect time by specifying a
1502 C<limit_dialect> key in the final hash as shown above.
1504 =head2 Working with PostgreSQL array types
1506 You can also assign values to PostgreSQL array columns by passing array
1507 references in the C<\%columns> (C<\%vals>) hashref of the
1508 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1511 $resultset->create({
1512 numbers => [1, 2, 3]
1517 numbers => [1, 2, 3]
1524 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1525 methods) you cannot directly use array references (since this is interpreted as
1526 a list of values to be C<OR>ed), but you can use the following syntax to force
1527 passing them as bind values:
1531 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1535 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1536 placeholders and bind values (subqueries)> for more explanation. Note that
1537 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1538 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1539 arrayrefs together with the column name, like this: C<< [column_name => value]
1542 =head1 BOOTSTRAPPING/MIGRATING
1544 =head2 Easy migration from class-based to schema-based setup
1546 You want to start using the schema-based approach to L<DBIx::Class>
1547 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1548 of existing classes that you don't want to move by hand. Try this nifty script
1552 use SQL::Translator;
1554 my $schema = MyDB->schema_instance;
1556 my $translator = SQL::Translator->new(
1557 debug => $debug || 0,
1558 trace => $trace || 0,
1559 no_comments => $no_comments || 0,
1560 show_warnings => $show_warnings || 0,
1561 add_drop_table => $add_drop_table || 0,
1562 validate => $validate || 0,
1564 'DBIx::Schema' => $schema,
1567 'prefix' => 'My::Schema',
1571 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1572 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1574 my $output = $translator->translate(@args) or die
1575 "Error: " . $translator->error;
1579 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1580 namespace, which is currently left as an exercise for the reader.
1582 =head1 OVERLOADING METHODS
1584 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1585 method calls, useful for things like default values and triggers. You have to
1586 use calls to C<next::method> to overload methods. More information on using
1587 L<Class::C3> with L<DBIx::Class> can be found in
1588 L<DBIx::Class::Manual::Component>.
1590 =head2 Setting default values for a row
1592 It's as simple as overriding the C<new> method. Note the use of
1596 my ( $class, $attrs ) = @_;
1598 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1600 my $new = $class->next::method($attrs);
1605 For more information about C<next::method>, look in the L<Class::C3>
1606 documentation. See also L<DBIx::Class::Manual::Component> for more
1607 ways to write your own base classes to do this.
1609 People looking for ways to do "triggers" with DBIx::Class are probably
1610 just looking for this.
1612 =head2 Changing one field whenever another changes
1614 For example, say that you have three columns, C<id>, C<number>, and
1615 C<squared>. You would like to make changes to C<number> and have
1616 C<squared> be automagically set to the value of C<number> squared.
1617 You can accomplish this by overriding C<store_column>:
1620 my ( $self, $name, $value ) = @_;
1621 if ($name eq 'number') {
1622 $self->squared($value * $value);
1624 $self->next::method($name, $value);
1627 Note that the hard work is done by the call to C<next::method>, which
1628 redispatches your call to store_column in the superclass(es).
1630 =head2 Automatically creating related objects
1632 You might have a class C<Artist> which has many C<CD>s. Further, if you
1633 want to create a C<CD> object every time you insert an C<Artist> object.
1634 You can accomplish this by overriding C<insert> on your objects:
1637 my ( $self, @args ) = @_;
1638 $self->next::method(@args);
1639 $self->cds->new({})->fill_from_artist($self)->insert;
1643 where C<fill_from_artist> is a method you specify in C<CD> which sets
1644 values in C<CD> based on the data in the C<Artist> object you pass in.
1646 =head2 Wrapping/overloading a column accessor
1650 Say you have a table "Camera" and want to associate a description
1651 with each camera. For most cameras, you'll be able to generate the description from
1652 the other columns. However, in a few special cases you may want to associate a
1653 custom description with a camera.
1657 In your database schema, define a description field in the "Camera" table that
1658 can contain text and null values.
1660 In DBIC, we'll overload the column accessor to provide a sane default if no
1661 custom description is defined. The accessor will either return or generate the
1662 description, depending on whether the field is null or not.
1664 First, in your "Camera" schema class, define the description field as follows:
1666 __PACKAGE__->add_columns(description => { accessor => '_description' });
1668 Next, we'll define the accessor-wrapper subroutine:
1673 # If there is an update to the column, we'll let the original accessor
1675 return $self->_description(@_) if @_;
1677 # Fetch the column value.
1678 my $description = $self->_description;
1680 # If there's something in the description field, then just return that.
1681 return $description if defined $description && length $descripton;
1683 # Otherwise, generate a description.
1684 return $self->generate_description;
1687 =head1 DEBUGGING AND PROFILING
1689 =head2 DBIx::Class objects with Data::Dumper
1691 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1692 be hard to find the pertinent data in all the data it can generate.
1693 Specifically, if one naively tries to use it like so,
1697 my $cd = $schema->resultset('CD')->find(1);
1700 several pages worth of data from the CD object's schema and result source will
1701 be dumped to the screen. Since usually one is only interested in a few column
1702 values of the object, this is not very helpful.
1704 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1705 it. Simply define a hook that L<Data::Dumper> will call on the object before
1706 dumping it. For example,
1713 result_source => undef,
1721 local $Data::Dumper::Freezer = '_dumper_hook';
1723 my $cd = $schema->resultset('CD')->find(1);
1725 # dumps $cd without its ResultSource
1727 If the structure of your schema is such that there is a common base class for
1728 all your table classes, simply put a method similar to C<_dumper_hook> in the
1729 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1730 will automagically clean up your data before printing it. See
1731 L<Data::Dumper/EXAMPLES> for more information.
1735 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1736 executed as well as notifications of query completion and transaction
1737 begin/commit. If you'd like to profile the SQL you can subclass the
1738 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1741 package My::Profiler;
1744 use base 'DBIx::Class::Storage::Statistics';
1746 use Time::HiRes qw(time);
1755 $self->print("Executing $sql: ".join(', ', @params)."\n");
1764 my $elapsed = sprintf("%0.4f", time() - $start);
1765 $self->print("Execution took $elapsed seconds.\n");
1771 You can then install that class as the debugging object:
1773 __PACKAGE__->storage->debugobj(new My::Profiler());
1774 __PACKAGE__->storage->debug(1);
1776 A more complicated example might involve storing each execution of SQL in an
1784 my $elapsed = time() - $start;
1785 push(@{ $calls{$sql} }, {
1791 You could then create average, high and low execution times for an SQL
1792 statement and dig down to see if certain parameters cause aberrant behavior.
1793 You might want to check out L<DBIx::Class::QueryLog> as well.
1795 =head1 STARTUP SPEED
1797 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1798 as the ORM loads all the relevant classes. This section examines
1799 techniques for reducing the startup delay.
1801 These tips are are listed in order of decreasing effectiveness - so the
1802 first tip, if applicable, should have the greatest effect on your
1805 =head2 Statically Define Your Schema
1808 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1809 classes dynamically based on the database schema then there will be a
1810 significant startup delay.
1812 For production use a statically defined schema (which can be generated
1813 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1814 the database schema once - see
1815 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1816 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1817 details on creating static schemas from a database).
1819 =head2 Move Common Startup into a Base Class
1821 Typically L<DBIx::Class> result classes start off with
1823 use base qw/DBIx::Class/;
1824 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1826 If this preamble is moved into a common base class:-
1830 use base qw/DBIx::Class/;
1831 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1834 and each result class then uses this as a base:-
1836 use base qw/MyDBICbase/;
1838 then the load_components is only performed once, which can result in a
1839 considerable startup speedup for schemas with many classes.
1841 =head2 Explicitly List Schema Result Classes
1843 The schema class will normally contain
1845 __PACKAGE__->load_classes();
1847 to load the result classes. This will use L<Module::Find|Module::Find>
1848 to find and load the appropriate modules. Explicitly defining the
1849 classes you wish to load will remove the overhead of
1850 L<Module::Find|Module::Find> and the related directory operations:-
1852 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1854 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1855 syntax to load the appropriate classes there is not a direct alternative
1856 avoiding L<Module::Find|Module::Find>.
1860 =head2 Cached statements
1862 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1863 This is normally a good idea, but if too many statements are cached, the database may use too much
1864 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1865 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1867 # print all currently cached prepared statements
1868 print for keys %{$schema->storage->dbh->{CachedKids}};
1869 # get a count of currently cached prepared statements
1870 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1872 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1875 my $kids = $schema->storage->dbh->{CachedKids};
1876 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1878 But what you probably want is to expire unused statements and not those that are used frequently.
1879 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1883 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1884 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },