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 Also note that C<prefetch> should only be used when you know you will
521 definitely use data from a related table. Pre-fetching related tables when you
522 only need columns from the main table will make performance worse!
524 =head2 Multiple joins
526 In the examples above, the C<join> attribute was a scalar. If you
527 pass an array reference instead, you can join to multiple tables. In
528 this example, we want to limit the search further, using
531 # Relationships defined elsewhere:
532 # CD->belongs_to('artist' => 'Artist');
533 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
534 my $rs = $schema->resultset('CD')->search(
536 'artist.name' => 'Bob Marley'
537 'liner_notes.notes' => { 'like', '%some text%' },
540 join => [qw/ artist liner_notes /],
541 order_by => [qw/ artist.name /],
546 # SELECT cd.*, artist.*, liner_notes.* FROM cd
547 # JOIN artist ON cd.artist = artist.id
548 # JOIN liner_notes ON cd.id = liner_notes.cd
549 # WHERE artist.name = 'Bob Marley'
550 # ORDER BY artist.name
552 =head2 Multi-step joins
554 Sometimes you want to join more than one relationship deep. In this example,
555 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
556 contain a specific string:
558 # Relationships defined elsewhere:
559 # Artist->has_many('cds' => 'CD', 'artist');
560 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
562 my $rs = $schema->resultset('Artist')->search(
564 'liner_notes.notes' => { 'like', '%some text%' },
568 'cds' => 'liner_notes'
574 # SELECT artist.* FROM artist
575 # LEFT JOIN cd ON artist.id = cd.artist
576 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
577 # WHERE liner_notes.notes LIKE '%some text%'
579 Joins can be nested to an arbitrary level. So if we decide later that we
580 want to reduce the number of Artists returned based on who wrote the liner
583 # Relationship defined elsewhere:
584 # LinerNotes->belongs_to('author' => 'Person');
586 my $rs = $schema->resultset('Artist')->search(
588 'liner_notes.notes' => { 'like', '%some text%' },
589 'author.name' => 'A. Writer'
594 'liner_notes' => 'author'
601 # SELECT artist.* FROM artist
602 # LEFT JOIN cd ON artist.id = cd.artist
603 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
604 # LEFT JOIN author ON author.id = liner_notes.author
605 # WHERE liner_notes.notes LIKE '%some text%'
606 # AND author.name = 'A. Writer'
608 =head2 Multi-step and multiple joins
610 With various combinations of array and hash references, you can join
611 tables in any combination you desire. For example, to join Artist to
612 CD and Concert, and join CD to LinerNotes:
614 # Relationships defined elsewhere:
615 # Artist->has_many('concerts' => 'Concert', 'artist');
617 my $rs = $schema->resultset('Artist')->search(
630 # SELECT artist.* FROM artist
631 # LEFT JOIN cd ON artist.id = cd.artist
632 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
633 # LEFT JOIN concert ON artist.id = concert.artist
635 =head2 Multi-step prefetch
637 C<prefetch> can be nested more than one relationship
638 deep using the same syntax as a multi-step join:
640 my $rs = $schema->resultset('Tag')->search(
650 # SELECT tag.*, cd.*, artist.* FROM tag
651 # JOIN cd ON tag.cd = cd.id
652 # JOIN artist ON cd.artist = artist.id
654 Now accessing our C<cd> and C<artist> relationships does not need additional
657 my $tag = $rs->first;
658 print $tag->cd->artist->name;
660 =head1 ROW-LEVEL OPERATIONS
662 =head2 Retrieving a row object's Schema
664 It is possible to get a Schema object from a row object like so:
666 my $schema = $cd->result_source->schema;
667 # use the schema as normal:
668 my $artist_rs = $schema->resultset('Artist');
670 This can be useful when you don't want to pass around a Schema object to every
673 =head2 Getting the value of the primary key for the last database insert
675 AKA getting last_insert_id
677 Thanks to the core component PK::Auto, this is straightforward:
679 my $foo = $rs->create(\%blah);
681 my $id = $foo->id; # foo->my_primary_key_field will also work.
683 If you are not using autoincrementing primary keys, this will probably
684 not work, but then you already know the value of the last primary key anyway.
686 =head2 Stringification
688 Employ the standard stringification technique by using the C<overload>
691 To make an object stringify itself as a single column, use something
692 like this (replace C<name> with the column/method of your choice):
694 use overload '""' => sub { shift->name}, fallback => 1;
696 For more complex stringification, you can use an anonymous subroutine:
698 use overload '""' => sub { $_[0]->name . ", " .
699 $_[0]->address }, fallback => 1;
701 =head3 Stringification Example
703 Suppose we have two tables: C<Product> and C<Category>. The table
706 Product(id, Description, category)
707 Category(id, Description)
709 C<category> is a foreign key into the Category table.
711 If you have a Product object C<$obj> and write something like
715 things will not work as expected.
717 To obtain, for example, the category description, you should add this
718 method to the class defining the Category table:
720 use overload "" => sub {
723 return $self->Description;
726 =head2 Want to know if find_or_create found or created a row?
728 Just use C<find_or_new> instead, then check C<in_storage>:
730 my $obj = $rs->find_or_new({ blah => 'blarg' });
731 unless ($obj->in_storage) {
733 # do whatever else you wanted if it was a new row
736 =head2 Dynamic Sub-classing DBIx::Class proxy classes
738 AKA multi-class object inflation from one table
740 L<DBIx::Class> classes are proxy classes, therefore some different
741 techniques need to be employed for more than basic subclassing. In
742 this example we have a single user table that carries a boolean bit
743 for admin. We would like like to give the admin users
744 objects(L<DBIx::Class::Row>) the same methods as a regular user but
745 also special admin only methods. It doesn't make sense to create two
746 seperate proxy-class files for this. We would be copying all the user
747 methods into the Admin class. There is a cleaner way to accomplish
750 Overriding the C<inflate_result> method within the User proxy-class
751 gives us the effect we want. This method is called by
752 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
753 grab the object being returned, inspect the values we are looking for,
754 bless it if it's an admin object, and then return it. See the example
761 use base qw/DBIx::Class::Schema/;
763 __PACKAGE__->load_namespaces;
766 B<Proxy-Class definitions>
768 package My::Schema::Result::User;
772 use base qw/DBIx::Class/;
774 ### Defined what our admin class is for ensure_class_loaded
775 my $admin_class = __PACKAGE__ . '::Admin';
777 __PACKAGE__->load_components(qw/Core/);
779 __PACKAGE__->table('users');
781 __PACKAGE__->add_columns(qw/user_id email password
782 firstname lastname active
785 __PACKAGE__->set_primary_key('user_id');
789 my $ret = $self->next::method(@_);
790 if( $ret->admin ) {### If this is an admin rebless for extra functions
791 $self->ensure_class_loaded( $admin_class );
792 bless $ret, $admin_class;
798 print "I am a regular user.\n";
803 package My::Schema::Result::User::Admin;
807 use base qw/My::Schema::Result::User/;
811 print "I am an admin.\n";
817 print "I am doing admin stuff\n";
827 my $user_data = { email => 'someguy@place.com',
831 my $admin_data = { email => 'someadmin@adminplace.com',
835 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
837 $schema->resultset('User')->create( $user_data );
838 $schema->resultset('User')->create( $admin_data );
840 ### Now we search for them
841 my $user = $schema->resultset('User')->single( $user_data );
842 my $admin = $schema->resultset('User')->single( $admin_data );
844 print ref $user, "\n";
845 print ref $admin, "\n";
847 print $user->password , "\n"; # pass1
848 print $admin->password , "\n";# pass2; inherited from User
849 print $user->hello , "\n";# I am a regular user.
850 print $admin->hello, "\n";# I am an admin.
852 ### The statement below will NOT print
853 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
854 ### The statement below will print
855 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
857 =head2 Skip row object creation for faster results
859 DBIx::Class is not built for speed, it's built for convenience and
860 ease of use, but sometimes you just need to get the data, and skip the
863 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
865 my $rs = $schema->resultset('CD');
867 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
869 my $hash_ref = $rs->find(1);
873 Beware, changing the Result class using
874 L<DBIx::Class::ResultSet/result_class> will replace any existing class
875 completely including any special components loaded using
876 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
878 =head2 Get raw data for blindingly fast results
880 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
881 above is not fast enough for you, you can use a DBIx::Class to return values
882 exactly as they come out of the database with none of the convenience methods
885 This is used like so:
887 my $cursor = $rs->cursor
888 while (my @vals = $cursor->next) {
889 # use $val[0..n] here
892 You will need to map the array offsets to particular columns (you can
893 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
895 =head1 RESULTSET OPERATIONS
897 =head2 Getting Schema from a ResultSet
899 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
901 $rs->result_source->schema
903 =head2 Getting Columns Of Data
907 If you want to find the sum of a particular column there are several
908 ways, the obvious one is to use search:
910 my $rs = $schema->resultset('Items')->search(
913 select => [ { sum => 'Cost' } ],
914 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
917 my $tc = $rs->first->get_column('total_cost');
919 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
920 returned when you ask the C<ResultSet> for a column using
923 my $cost = $schema->resultset('Items')->get_column('Cost');
926 With this you can also do:
928 my $minvalue = $cost->min;
929 my $maxvalue = $cost->max;
931 Or just iterate through the values of this column only:
933 while ( my $c = $cost->next ) {
937 foreach my $c ($cost->all) {
941 C<ResultSetColumn> only has a limited number of built-in functions, if
942 you need one that it doesn't have, then you can use the C<func> method
945 my $avg = $cost->func('AVERAGE');
947 This will cause the following SQL statement to be run:
949 SELECT AVERAGE(Cost) FROM Items me
951 Which will of course only work if your database supports this function.
952 See L<DBIx::Class::ResultSetColumn> for more documentation.
954 =head2 Creating a result set from a set of rows
956 Sometimes you have a (set of) row objects that you want to put into a
957 resultset without the need to hit the DB again. You can do that by using the
958 L<set_cache|DBIx::Class::Resultset/set_cache> method:
960 my @uploadable_groups;
961 while (my $group = $groups->next) {
962 if ($group->can_upload($self)) {
963 push @uploadable_groups, $group;
966 my $new_rs = $self->result_source->resultset;
967 $new_rs->set_cache(\@uploadable_groups);
971 =head1 USING RELATIONSHIPS
973 =head2 Create a new row in a related table
975 my $author = $book->create_related('author', { name => 'Fred'});
977 =head2 Search in a related table
979 Only searches for books named 'Titanic' by the author in $author.
981 my $books_rs = $author->search_related('books', { name => 'Titanic' });
983 =head2 Delete data in a related table
985 Deletes only the book named Titanic by the author in $author.
987 $author->delete_related('books', { name => 'Titanic' });
989 =head2 Ordering a relationship result set
991 If you always want a relation to be ordered, you can specify this when you
992 create the relationship.
994 To order C<< $book->pages >> by descending page_number, create the relation
997 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
999 =head2 Filtering a relationship result set
1001 If you want to get a filtered result set, you can just add add to $attr as follows:
1003 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1005 =head2 Many-to-many relationships
1007 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1010 use base 'DBIx::Class';
1011 __PACKAGE__->load_components('Core');
1012 __PACKAGE__->table('user');
1013 __PACKAGE__->add_columns(qw/id name/);
1014 __PACKAGE__->set_primary_key('id');
1015 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1016 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1018 package My::UserAddress;
1019 use base 'DBIx::Class';
1020 __PACKAGE__->load_components('Core');
1021 __PACKAGE__->table('user_address');
1022 __PACKAGE__->add_columns(qw/user address/);
1023 __PACKAGE__->set_primary_key(qw/user address/);
1024 __PACKAGE__->belongs_to('user' => 'My::User');
1025 __PACKAGE__->belongs_to('address' => 'My::Address');
1027 package My::Address;
1028 use base 'DBIx::Class';
1029 __PACKAGE__->load_components('Core');
1030 __PACKAGE__->table('address');
1031 __PACKAGE__->add_columns(qw/id street town area_code country/);
1032 __PACKAGE__->set_primary_key('id');
1033 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1034 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1036 $rs = $user->addresses(); # get all addresses for a user
1037 $rs = $address->users(); # get all users for an address
1039 =head2 Relationships across DB schemas
1041 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1042 is easy as long as the schemas themselves are all accessible via the same DBI
1043 connection. In most cases, this means that they are on the same database host
1044 as each other and your connecting database user has the proper permissions to them.
1046 To accomplish this one only needs to specify the DB schema name in the table
1047 declaration, like so...
1049 package MyDatabase::Main::Artist;
1050 use base qw/DBIx::Class/;
1051 __PACKAGE__->load_components(qw/PK::Auto Core/);
1053 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1055 __PACKAGE__->add_columns(qw/ artistid name /);
1056 __PACKAGE__->set_primary_key('artistid');
1057 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1061 Whatever string you specify there will be used to build the "FROM" clause in SQL
1064 The big drawback to this is you now have DB schema names hardcoded in your
1065 class files. This becomes especially troublesome if you have multiple instances
1066 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1067 the DB schemas are named based on the environment (e.g. database1_dev).
1069 However, one can dynamically "map" to the proper DB schema by overriding the
1070 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1071 building a renaming facility, like so:
1073 package MyDatabase::Schema;
1076 extends 'DBIx::Class::Schema';
1078 around connection => sub {
1079 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1081 my $postfix = delete $attr->{schema_name_postfix};
1086 $self->append_db_name($postfix);
1090 sub append_db_name {
1091 my ( $self, $postfix ) = @_;
1095 { $_->name =~ /^\w+\./mx }
1097 { $self->source($_) }
1100 foreach my $source (@sources_with_db) {
1101 my $name = $source->name;
1102 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1104 $source->name($name);
1110 By overridding the L<connection|DBIx::Class::Schama/connection>
1111 method and extracting a custom option from the provided \%attr hashref one can
1112 then simply iterate over all the Schema's ResultSources, renaming them as
1115 To use this facility, simply add or modify the \%attr hashref that is passed to
1116 L<connection|DBIx::Class::Schama/connect>, as follows:
1119 = MyDatabase::Schema->connect(
1124 schema_name_postfix => '_dev'
1125 # ... Other options as desired ...
1128 Obviously, one could accomplish even more advanced mapping via a hash map or a
1133 As of version 0.04001, there is improved transaction support in
1134 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1135 example of the recommended way to use it:
1137 my $genus = $schema->resultset('Genus')->find(12);
1139 my $coderef2 = sub {
1144 my $coderef1 = sub {
1145 $genus->add_to_species({ name => 'troglodyte' });
1148 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1149 return $genus->species;
1154 $rs = $schema->txn_do($coderef1);
1157 if ($@) { # Transaction failed
1158 die "the sky is falling!" #
1159 if ($@ =~ /Rollback failed/); # Rollback failed
1161 deal_with_failed_transaction();
1164 Nested transactions will work as expected. That is, only the outermost
1165 transaction will actually issue a commit to the $dbh, and a rollback
1166 at any level of any transaction will cause the entire nested
1167 transaction to fail. Support for savepoints and for true nested
1168 transactions (for databases that support them) will hopefully be added
1173 =head2 Creating Schemas From An Existing Database
1175 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1176 L<DBIx::Class::Schema> and associated sources by examining the database.
1178 The recommend way of achieving this is to use the
1179 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1181 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1182 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1184 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1185 source definitions for all the tables found in the C<foo> database.
1187 =head2 Creating DDL SQL
1189 The following functionality requires you to have L<SQL::Translator>
1190 (also known as "SQL Fairy") installed.
1192 To create a set of database-specific .sql files for the above schema:
1194 my $schema = My::Schema->connect($dsn);
1195 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1200 By default this will create schema files in the current directory, for
1201 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1203 To create a new database using the schema:
1205 my $schema = My::Schema->connect($dsn);
1206 $schema->deploy({ add_drop_tables => 1});
1208 To import created .sql files using the mysql client:
1210 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1212 To create C<ALTER TABLE> conversion scripts to update a database to a
1213 newer version of your schema at a later point, first set a new
1214 C<$VERSION> in your Schema file, then:
1216 my $schema = My::Schema->connect($dsn);
1217 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1223 This will produce new database-specific .sql files for the new version
1224 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1225 requires that the files for 0.1 as created above are available in the
1226 given directory to diff against.
1228 =head2 Select from dual
1230 Dummy tables are needed by some databases to allow calling functions
1231 or expressions that aren't based on table content, for examples of how
1232 this applies to various database types, see:
1233 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1235 Note: If you're using Oracles dual table don't B<ever> do anything
1236 other than a select, if you CRUD on your dual table you *will* break
1239 Make a table class as you would for any other table
1241 package MyAppDB::Dual;
1244 use base 'DBIx::Class';
1245 __PACKAGE__->load_components("Core");
1246 __PACKAGE__->table("Dual");
1247 __PACKAGE__->add_columns(
1249 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1252 Once you've loaded your table class select from it using C<select>
1253 and C<as> instead of C<columns>
1255 my $rs = $schema->resultset('Dual')->search(undef,
1256 { select => [ 'sydate' ],
1261 All you have to do now is be careful how you access your resultset, the below
1262 will not work because there is no column called 'now' in the Dual table class
1264 while (my $dual = $rs->next) {
1265 print $dual->now."\n";
1267 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1269 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1270 your Dual class for whatever you wanted to select from dual, but that's just
1271 silly, instead use C<get_column>
1273 while (my $dual = $rs->next) {
1274 print $dual->get_column('now')."\n";
1279 my $cursor = $rs->cursor;
1280 while (my @vals = $cursor->next) {
1281 print $vals[0]."\n";
1284 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1285 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1286 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1287 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1288 L<SQL::Translator> to not create table dual:
1291 add_drop_table => 1,
1292 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1294 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1296 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1298 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1299 while ( my $dual = $rs->next ) {
1300 print $dual->{now}."\n";
1303 Here are some example C<select> conditions to illustrate the different syntax
1304 you could use for doing stuff like
1305 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1307 # get a sequence value
1308 select => [ 'A_SEQ.nextval' ],
1310 # get create table sql
1311 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1313 # get a random num between 0 and 100
1314 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1317 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1320 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1322 # which day of the week were you born on?
1323 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1325 # select 16 rows from dual
1326 select => [ "'hello'" ],
1328 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1332 =head2 Adding Indexes And Functions To Your SQL
1334 Often you will want indexes on columns on your table to speed up searching. To
1335 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1336 class (refer to the advanced
1337 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1338 to share a hook between multiple sources):
1340 package My::Schema::Result::Artist;
1342 __PACKAGE__->table('artist');
1343 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1345 sub sqlt_deploy_hook {
1346 my ($self, $sqlt_table) = @_;
1348 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1353 Sometimes you might want to change the index depending on the type of the
1354 database for which SQL is being generated:
1356 my ($db_type = $sqlt_table->schema->translator->producer_type)
1357 =~ s/^SQL::Translator::Producer:://;
1359 You can also add hooks to the schema level to stop certain tables being
1366 sub sqlt_deploy_hook {
1367 my ($self, $sqlt_schema) = @_;
1369 $sqlt_schema->drop_table('table_name');
1372 You could also add views, procedures or triggers to the output using
1373 L<SQL::Translator::Schema/add_view>,
1374 L<SQL::Translator::Schema/add_procedure> or
1375 L<SQL::Translator::Schema/add_trigger>.
1378 =head2 Schema versioning
1380 The following example shows simplistically how you might use DBIx::Class to
1381 deploy versioned schemas to your customers. The basic process is as follows:
1387 Create a DBIx::Class schema
1399 Modify schema to change functionality
1403 Deploy update to customers
1407 B<Create a DBIx::Class schema>
1409 This can either be done manually, or generated from an existing database as
1410 described under L</Creating Schemas From An Existing Database>
1414 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1416 B<Deploy to customers>
1418 There are several ways you could deploy your schema. These are probably
1419 beyond the scope of this recipe, but might include:
1425 Require customer to apply manually using their RDBMS.
1429 Package along with your app, making database dump/schema update/tests
1430 all part of your install.
1434 B<Modify the schema to change functionality>
1436 As your application evolves, it may be necessary to modify your schema
1437 to change functionality. Once the changes are made to your schema in
1438 DBIx::Class, export the modified schema and the conversion scripts as
1439 in L</Creating DDL SQL>.
1441 B<Deploy update to customers>
1443 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1444 Schema class. This will add a new table to your database called
1445 C<dbix_class_schema_vesion> which will keep track of which version is installed
1446 and warn if the user trys to run a newer schema version than the
1447 database thinks it has.
1449 Alternatively, you can send the conversion sql scripts to your
1452 =head2 Setting quoting for the generated SQL.
1454 If the database contains column names with spaces and/or reserved words, they
1455 need to be quoted in the SQL queries. This is done using:
1457 __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
1458 __PACKAGE__->storage->sql_maker->name_sep('.');
1460 The first sets the quote characters. Either a pair of matching
1461 brackets, or a C<"> or C<'>:
1463 __PACKAGE__->storage->sql_maker->quote_char('"');
1465 Check the documentation of your database for the correct quote
1466 characters to use. C<name_sep> needs to be set to allow the SQL
1467 generator to put the quotes the correct place.
1469 In most cases you should set these as part of the arguments passed to
1470 L<DBIx::Class::Schema/connect>:
1472 my $schema = My::Schema->connect(
1482 =head2 Setting limit dialect for SQL::Abstract::Limit
1484 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1485 the remote SQL server by looking at the database handle. This is a
1486 common problem when using the DBD::JDBC, since the DBD-driver only
1487 know that in has a Java-driver available, not which JDBC driver the
1488 Java component has loaded. This specifically sets the limit_dialect
1489 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1492 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1494 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1495 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1497 The limit dialect can also be set at connect time by specifying a
1498 C<limit_dialect> key in the final hash as shown above.
1500 =head2 Working with PostgreSQL array types
1502 You can also assign values to PostgreSQL array columns by passing array
1503 references in the C<\%columns> (C<\%vals>) hashref of the
1504 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1507 $resultset->create({
1508 numbers => [1, 2, 3]
1513 numbers => [1, 2, 3]
1520 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1521 methods) you cannot directly use array references (since this is interpreted as
1522 a list of values to be C<OR>ed), but you can use the following syntax to force
1523 passing them as bind values:
1527 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1531 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1532 placeholders and bind values (subqueries)> for more explanation. Note that
1533 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1534 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1535 arrayrefs together with the column name, like this: C<< [column_name => value]
1538 =head1 BOOTSTRAPPING/MIGRATING
1540 =head2 Easy migration from class-based to schema-based setup
1542 You want to start using the schema-based approach to L<DBIx::Class>
1543 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1544 of existing classes that you don't want to move by hand. Try this nifty script
1548 use SQL::Translator;
1550 my $schema = MyDB->schema_instance;
1552 my $translator = SQL::Translator->new(
1553 debug => $debug || 0,
1554 trace => $trace || 0,
1555 no_comments => $no_comments || 0,
1556 show_warnings => $show_warnings || 0,
1557 add_drop_table => $add_drop_table || 0,
1558 validate => $validate || 0,
1560 'DBIx::Schema' => $schema,
1563 'prefix' => 'My::Schema',
1567 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1568 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1570 my $output = $translator->translate(@args) or die
1571 "Error: " . $translator->error;
1575 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1576 namespace, which is currently left as an exercise for the reader.
1578 =head1 OVERLOADING METHODS
1580 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1581 method calls, useful for things like default values and triggers. You have to
1582 use calls to C<next::method> to overload methods. More information on using
1583 L<Class::C3> with L<DBIx::Class> can be found in
1584 L<DBIx::Class::Manual::Component>.
1586 =head2 Setting default values for a row
1588 It's as simple as overriding the C<new> method. Note the use of
1592 my ( $class, $attrs ) = @_;
1594 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1596 my $new = $class->next::method($attrs);
1601 For more information about C<next::method>, look in the L<Class::C3>
1602 documentation. See also L<DBIx::Class::Manual::Component> for more
1603 ways to write your own base classes to do this.
1605 People looking for ways to do "triggers" with DBIx::Class are probably
1606 just looking for this.
1608 =head2 Changing one field whenever another changes
1610 For example, say that you have three columns, C<id>, C<number>, and
1611 C<squared>. You would like to make changes to C<number> and have
1612 C<squared> be automagically set to the value of C<number> squared.
1613 You can accomplish this by overriding C<store_column>:
1616 my ( $self, $name, $value ) = @_;
1617 if ($name eq 'number') {
1618 $self->squared($value * $value);
1620 $self->next::method($name, $value);
1623 Note that the hard work is done by the call to C<next::method>, which
1624 redispatches your call to store_column in the superclass(es).
1626 =head2 Automatically creating related objects
1628 You might have a class C<Artist> which has many C<CD>s. Further, if you
1629 want to create a C<CD> object every time you insert an C<Artist> object.
1630 You can accomplish this by overriding C<insert> on your objects:
1633 my ( $self, @args ) = @_;
1634 $self->next::method(@args);
1635 $self->cds->new({})->fill_from_artist($self)->insert;
1639 where C<fill_from_artist> is a method you specify in C<CD> which sets
1640 values in C<CD> based on the data in the C<Artist> object you pass in.
1642 =head2 Wrapping/overloading a column accessor
1646 Say you have a table "Camera" and want to associate a description
1647 with each camera. For most cameras, you'll be able to generate the description from
1648 the other columns. However, in a few special cases you may want to associate a
1649 custom description with a camera.
1653 In your database schema, define a description field in the "Camera" table that
1654 can contain text and null values.
1656 In DBIC, we'll overload the column accessor to provide a sane default if no
1657 custom description is defined. The accessor will either return or generate the
1658 description, depending on whether the field is null or not.
1660 First, in your "Camera" schema class, define the description field as follows:
1662 __PACKAGE__->add_columns(description => { accessor => '_description' });
1664 Next, we'll define the accessor-wrapper subroutine:
1669 # If there is an update to the column, we'll let the original accessor
1671 return $self->_description(@_) if @_;
1673 # Fetch the column value.
1674 my $description = $self->_description;
1676 # If there's something in the description field, then just return that.
1677 return $description if defined $description && length $descripton;
1679 # Otherwise, generate a description.
1680 return $self->generate_description;
1683 =head1 DEBUGGING AND PROFILING
1685 =head2 DBIx::Class objects with Data::Dumper
1687 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1688 be hard to find the pertinent data in all the data it can generate.
1689 Specifically, if one naively tries to use it like so,
1693 my $cd = $schema->resultset('CD')->find(1);
1696 several pages worth of data from the CD object's schema and result source will
1697 be dumped to the screen. Since usually one is only interested in a few column
1698 values of the object, this is not very helpful.
1700 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1701 it. Simply define a hook that L<Data::Dumper> will call on the object before
1702 dumping it. For example,
1709 result_source => undef,
1717 local $Data::Dumper::Freezer = '_dumper_hook';
1719 my $cd = $schema->resultset('CD')->find(1);
1721 # dumps $cd without its ResultSource
1723 If the structure of your schema is such that there is a common base class for
1724 all your table classes, simply put a method similar to C<_dumper_hook> in the
1725 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1726 will automagically clean up your data before printing it. See
1727 L<Data::Dumper/EXAMPLES> for more information.
1731 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1732 executed as well as notifications of query completion and transaction
1733 begin/commit. If you'd like to profile the SQL you can subclass the
1734 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1737 package My::Profiler;
1740 use base 'DBIx::Class::Storage::Statistics';
1742 use Time::HiRes qw(time);
1751 $self->print("Executing $sql: ".join(', ', @params)."\n");
1760 my $elapsed = sprintf("%0.4f", time() - $start);
1761 $self->print("Execution took $elapsed seconds.\n");
1767 You can then install that class as the debugging object:
1769 __PACKAGE__->storage->debugobj(new My::Profiler());
1770 __PACKAGE__->storage->debug(1);
1772 A more complicated example might involve storing each execution of SQL in an
1780 my $elapsed = time() - $start;
1781 push(@{ $calls{$sql} }, {
1787 You could then create average, high and low execution times for an SQL
1788 statement and dig down to see if certain parameters cause aberrant behavior.
1789 You might want to check out L<DBIx::Class::QueryLog> as well.
1791 =head1 STARTUP SPEED
1793 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1794 as the ORM loads all the relevant classes. This section examines
1795 techniques for reducing the startup delay.
1797 These tips are are listed in order of decreasing effectiveness - so the
1798 first tip, if applicable, should have the greatest effect on your
1801 =head2 Statically Define Your Schema
1804 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1805 classes dynamically based on the database schema then there will be a
1806 significant startup delay.
1808 For production use a statically defined schema (which can be generated
1809 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1810 the database schema once - see
1811 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1812 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1813 details on creating static schemas from a database).
1815 =head2 Move Common Startup into a Base Class
1817 Typically L<DBIx::Class> result classes start off with
1819 use base qw/DBIx::Class/;
1820 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1822 If this preamble is moved into a common base class:-
1826 use base qw/DBIx::Class/;
1827 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1830 and each result class then uses this as a base:-
1832 use base qw/MyDBICbase/;
1834 then the load_components is only performed once, which can result in a
1835 considerable startup speedup for schemas with many classes.
1837 =head2 Explicitly List Schema Result Classes
1839 The schema class will normally contain
1841 __PACKAGE__->load_classes();
1843 to load the result classes. This will use L<Module::Find|Module::Find>
1844 to find and load the appropriate modules. Explicitly defining the
1845 classes you wish to load will remove the overhead of
1846 L<Module::Find|Module::Find> and the related directory operations:-
1848 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1850 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1851 syntax to load the appropriate classes there is not a direct alternative
1852 avoiding L<Module::Find|Module::Find>.
1856 =head2 Cached statements
1858 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1859 This is normally a good idea, but if too many statements are cached, the database may use too much
1860 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1861 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1863 # print all currently cached prepared statements
1864 print for keys %{$schema->storage->dbh->{CachedKids}};
1865 # get a count of currently cached prepared statements
1866 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1868 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1871 my $kids = $schema->storage->dbh->{CachedKids};
1872 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1874 But what you probably want is to expire unused statements and not those that are used frequently.
1875 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1879 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1880 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },