3 DBIx::Class::Manual::Cookbook - Miscellaneous recipes
9 When you expect a large number of results, you can ask L<DBIx::Class> for a
10 paged resultset, which will fetch only a defined number of records at a time:
12 my $rs = $schema->resultset('Artist')->search(
15 page => 1, # page to return (defaults to 1)
16 rows => 10, # number of results per page
20 return $rs->all(); # all records for page 1
22 return $rs->page(2); # records for page 2
24 You can get a L<Data::Page> object for the resultset (suitable for use
25 in e.g. a template) using the C<pager> method:
29 =head2 Complex WHERE clauses
31 Sometimes you need to formulate a query using specific operators:
33 my @albums = $schema->resultset('Album')->search({
34 artist => { 'like', '%Lamb%' },
35 title => { 'like', '%Fear of Fours%' },
38 This results in something like the following C<WHERE> clause:
40 WHERE artist LIKE ? AND title LIKE ?
42 And the following bind values for the placeholders: C<'%Lamb%'>, C<'%Fear of
45 Other queries might require slightly more complex logic:
47 my @albums = $schema->resultset('Album')->search({
50 artist => { 'like', '%Smashing Pumpkins%' },
51 title => 'Siamese Dream',
53 artist => 'Starchildren',
57 This results in the following C<WHERE> clause:
59 WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
60 OR artist = 'Starchildren'
62 For more information on generating complex queries, see
63 L<SQL::Abstract/WHERE CLAUSES>.
65 =head2 Retrieve one and only one row from a resultset
67 Sometimes you need only the first "top" row of a resultset. While this
68 can be easily done with L<< $rs->first|DBIx::Class::ResultSet/first
69 >>, it is suboptimal, as a full blown cursor for the resultset will be
70 created and then immediately destroyed after fetching the first row
71 object. L<< $rs->single|DBIx::Class::ResultSet/single >> is designed
72 specifically for this case - it will grab the first returned result
73 without even instantiating a cursor.
75 Before replacing all your calls to C<first()> with C<single()> please observe the
82 While single() takes a search condition just like search() does, it does
83 _not_ accept search attributes. However one can always chain a single() to
86 my $top_cd = $cd_rs->search({}, { order_by => 'rating' })->single;
91 Since single() is the engine behind find(), it is designed to fetch a
92 single row per database query. Thus a warning will be issued when the
93 underlying SELECT returns more than one row. Sometimes however this usage
94 is valid: i.e. we have an arbitrary number of cd's but only one of them is
95 at the top of the charts at any given time. If you know what you are doing,
96 you can silence the warning by explicitly limiting the resultset size:
98 my $top_cd = $cd_rs->search ({}, { order_by => 'rating', rows => 1 })->single;
102 =head2 Arbitrary SQL through a custom ResultSource
104 Sometimes you have to run arbitrary SQL because your query is too complex
105 (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
106 be optimized for your database in a special way, but you still want to
107 get the results as a L<DBIx::Class::ResultSet>.
109 This is accomplished by defining a
110 L<ResultSource::View|DBIx::Class::ResultSource::View> for your query,
111 almost like you would define a regular ResultSource.
113 package My::Schema::Result::UserFriendsComplex;
116 use base qw/DBIx::Class/;
118 __PACKAGE__->load_components('Core');
119 __PACKAGE__->table_class('DBIx::Class::ResultSource::View');
121 # ->table, ->add_columns, etc.
123 # do not attempt to deploy() this view
124 __PACKAGE__->result_source_instance->is_virtual(1);
126 __PACKAGE__->result_source_instance->view_definition(q[
127 SELECT u.* FROM user u
128 INNER JOIN user_friends f ON u.id = f.user_id
129 WHERE f.friend_user_id = ?
131 SELECT u.* FROM user u
132 INNER JOIN user_friends f ON u.id = f.friend_user_id
136 Next, you can execute your complex query using bind parameters like this:
138 my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
140 bind => [ 12345, 12345 ]
144 ... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
145 that you cannot modify the rows it contains, ie. cannot call L</update>,
146 L</delete>, ... on it).
148 Note that you cannot have bind parameters unless is_virtual is set to true.
154 If you're using the old deprecated C<< $rsrc_instance->name(\'( SELECT ...') >>
155 method for custom SQL execution, you are highly encouraged to update your code
156 to use a virtual view as above. If you do not want to change your code, and just
157 want to suppress the deprecation warning when you call
158 L<DBIx::Class::Schema/deploy>, add this line to your source definition, so that
159 C<deploy> will exclude this "table":
161 sub sqlt_deploy_hook { $_[1]->schema->drop_table ($_[1]) }
165 =head2 Using specific columns
167 When you only want specific columns from a table, you can use
168 C<columns> to specify which ones you need. This is useful to avoid
169 loading columns with large amounts of data that you aren't about to
172 my $rs = $schema->resultset('Artist')->search(
175 columns => [qw/ name /]
180 # SELECT artist.name FROM artist
182 This is a shortcut for C<select> and C<as>, see below. C<columns>
183 cannot be used together with C<select> and C<as>.
185 =head2 Using database functions or stored procedures
187 The combination of C<select> and C<as> can be used to return the result of a
188 database function or stored procedure as a column value. You use C<select> to
189 specify the source for your column value (e.g. a column name, function, or
190 stored procedure name). You then use C<as> to set the column name you will use
191 to access the returned value:
193 my $rs = $schema->resultset('Artist')->search(
196 select => [ 'name', { LENGTH => 'name' } ],
197 as => [qw/ name name_length /],
202 # SELECT name name, LENGTH( name )
205 Note that the C<as> attribute B<has absolutely nothing to do> with the sql
206 syntax C< SELECT foo AS bar > (see the documentation in
207 L<DBIx::Class::ResultSet/ATTRIBUTES>). You can control the C<AS> part of the
208 generated SQL via the C<-as> field attribute as follows:
210 my $rs = $schema->resultset('Artist')->search(
215 '+select' => [ { count => 'cds.cdid', -as => 'amount_of_cds' } ],
216 '+as' => [qw/num_cds/],
217 order_by => { -desc => 'amount_of_cds' },
222 # SELECT me.artistid, me.name, me.rank, me.charfield, COUNT( cds.cdid ) AS amount_of_cds
223 # FROM artist me LEFT JOIN cd cds ON cds.artist = me.artistid
224 # GROUP BY me.artistid, me.name, me.rank, me.charfield
225 # ORDER BY amount_of_cds DESC
228 If your alias exists as a column in your base class (i.e. it was added with
229 L<add_columns|DBIx::Class::ResultSource/add_columns>), you just access it as
230 normal. Our C<Artist> class has a C<name> column, so we just use the C<name>
233 my $artist = $rs->first();
234 my $name = $artist->name();
236 If on the other hand the alias does not correspond to an existing column, you
237 have to fetch the value using the C<get_column> accessor:
239 my $name_length = $artist->get_column('name_length');
241 If you don't like using C<get_column>, you can always create an accessor for
242 any of your aliases using either of these:
244 # Define accessor manually:
245 sub name_length { shift->get_column('name_length'); }
247 # Or use DBIx::Class::AccessorGroup:
248 __PACKAGE__->mk_group_accessors('column' => 'name_length');
250 See also L</Using SQL functions on the left hand side of a comparison>.
252 =head2 SELECT DISTINCT with multiple columns
254 my $rs = $schema->resultset('Artist')->search(
257 columns => [ qw/artist_id name rank/ ],
262 my $rs = $schema->resultset('Artist')->search(
265 columns => [ qw/artist_id name rank/ ],
266 group_by => [ qw/artist_id name rank/ ],
271 # SELECT me.artist_id, me.name, me.rank
273 # GROUP BY artist_id, name, rank
275 =head2 SELECT COUNT(DISTINCT colname)
277 my $rs = $schema->resultset('Artist')->search(
280 columns => [ qw/name/ ],
285 my $rs = $schema->resultset('Artist')->search(
288 columns => [ qw/name/ ],
289 group_by => [ qw/name/ ],
293 my $count = $rs->count;
296 # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) count_subq:
298 =head2 Grouping results
300 L<DBIx::Class> supports C<GROUP BY> as follows:
302 my $rs = $schema->resultset('Artist')->search(
306 select => [ 'name', { count => 'cds.id' } ],
307 as => [qw/ name cd_count /],
308 group_by => [qw/ name /]
313 # SELECT name, COUNT( cd.id ) FROM artist
314 # LEFT JOIN cd ON artist.id = cd.artist
317 Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
318 are in any way unsure about the use of the attributes above (C< join
319 >, C< select >, C< as > and C< group_by >).
321 =head2 Subqueries (EXPERIMENTAL)
323 You can write subqueries relatively easily in DBIC.
325 my $inside_rs = $schema->resultset('Artist')->search({
326 name => [ 'Billy Joel', 'Brittany Spears' ],
329 my $rs = $schema->resultset('CD')->search({
330 artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
333 The usual operators ( =, !=, IN, NOT IN, etc) are supported.
335 B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
336 The following will B<not> work:
338 my $rs = $schema->resultset('CD')->search({
339 artist_id => $inside_rs->get_column('id')->as_query, # does NOT work
344 Subqueries are supported in the where clause (first hashref), and in the
345 from, select, and +select attributes.
347 =head3 Correlated subqueries
349 my $cdrs = $schema->resultset('CD');
350 my $rs = $cdrs->search({
352 '=' => $cdrs->search(
353 { artist_id => { '=' => \'me.artist_id' } },
355 )->get_column('year')->max_rs->as_query,
359 That creates the following SQL:
361 SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
364 SELECT MAX(inner.year)
366 WHERE artist_id = me.artist_id
371 Please note that subqueries are considered an experimental feature.
373 =head2 Predefined searches
375 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
376 and defining often used searches as methods:
378 package My::DBIC::ResultSet::CD;
381 use base 'DBIx::Class::ResultSet';
383 sub search_cds_ordered {
386 return $self->search(
388 { order_by => 'name DESC' },
394 To use your resultset, first tell DBIx::Class to create an instance of it
395 for you, in your My::DBIC::Schema::CD class:
397 # class definition as normal
398 __PACKAGE__->load_components(qw/ Core /);
399 __PACKAGE__->table('cd');
401 # tell DBIC to use the custom ResultSet class
402 __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
404 Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
406 Then call your new method in your code:
408 my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
410 =head2 Using SQL functions on the left hand side of a comparison
412 Using SQL functions on the left hand side of a comparison is generally not a
413 good idea since it requires a scan of the entire table. (Unless your RDBMS
414 supports indexes on expressions - including return values of functions -, and
415 you create an index on the return value of the function in question.) However,
416 it can be accomplished with C<DBIx::Class> when necessary.
418 If you do not have quoting on, simply include the function in your search
419 specification as you would any column:
421 $rs->search({ 'YEAR(date_of_birth)' => 1979 });
423 With quoting on, or for a more portable solution, use literal SQL values with
426 $rs->search(\[ 'YEAR(date_of_birth) = ?', [ date_of_birth => 1979 ] ]);
429 # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
433 -nest => \[ 'YEAR(date_of_birth) = ?', [ date_of_birth => 1979 ] ],
437 # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
439 Note: the C<date_of_birth> string in the C<< [ date_of_birth => 1979 ] >> part
440 should be the same as the name of the column. It is used by L<DBIx::Class> to
441 handle special column types. (If no column is involved in your expression, just
442 invent a column name.)
444 See also L<SQL::Abstract/Literal SQL with placeholders and bind values
447 =head1 JOINS AND PREFETCHING
449 =head2 Using joins and prefetch
451 You can use the C<join> attribute to allow searching on, or sorting your
452 results by, one or more columns in a related table.
454 This requires that you have defined the L<DBIx::Class::Relationship>. For example :
456 My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
458 To return all CDs matching a particular artist name, you specify the name of the relationship ('artists'):
460 my $rs = $schema->resultset('CD')->search(
462 'artists.name' => 'Bob Marley'
465 join => 'artists', # join the artist table
470 # SELECT cd.* FROM cd
471 # JOIN artist ON cd.artist = artist.id
472 # WHERE artist.name = 'Bob Marley'
474 In that example both the join, and the condition use the relationship name rather than the table name
475 (see L<DBIx::Class::Manual::Joining> for more details on aliasing ).
477 If required, you can now sort on any column in the related tables by including
478 it in your C<order_by> attribute, (again using the aliased relation name rather than table name) :
480 my $rs = $schema->resultset('CD')->search(
482 'artists.name' => 'Bob Marley'
486 order_by => [qw/ artists.name /]
491 # SELECT cd.* FROM cd
492 # JOIN artist ON cd.artist = artist.id
493 # WHERE artist.name = 'Bob Marley'
494 # ORDER BY artist.name
496 Note that the C<join> attribute should only be used when you need to search or
497 sort using columns in a related table. Joining related tables when you only
498 need columns from the main table will make performance worse!
500 Now let's say you want to display a list of CDs, each with the name of the
501 artist. The following will work fine:
503 while (my $cd = $rs->next) {
504 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
507 There is a problem however. We have searched both the C<cd> and C<artist> tables
508 in our main query, but we have only returned data from the C<cd> table. To get
509 the artist name for any of the CD objects returned, L<DBIx::Class> will go back
512 SELECT artist.* FROM artist WHERE artist.id = ?
514 A statement like the one above will run for each and every CD returned by our
515 main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
518 Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
519 This allows you to fetch results from related tables in advance:
521 my $rs = $schema->resultset('CD')->search(
523 'artists.name' => 'Bob Marley'
527 order_by => [qw/ artists.name /],
528 prefetch => 'artists' # return artist data too!
532 # Equivalent SQL (note SELECT from both "cd" and "artist"):
533 # SELECT cd.*, artist.* FROM cd
534 # JOIN artist ON cd.artist = artist.id
535 # WHERE artist.name = 'Bob Marley'
536 # ORDER BY artist.name
538 The code to print the CD list remains the same:
540 while (my $cd = $rs->next) {
541 print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
544 L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
545 so no additional SQL statements are executed. You now have a much more
548 Also note that C<prefetch> should only be used when you know you will
549 definitely use data from a related table. Pre-fetching related tables when you
550 only need columns from the main table will make performance worse!
552 =head2 Multiple joins
554 In the examples above, the C<join> attribute was a scalar. If you
555 pass an array reference instead, you can join to multiple tables. In
556 this example, we want to limit the search further, using
559 # Relationships defined elsewhere:
560 # CD->belongs_to('artist' => 'Artist');
561 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
562 my $rs = $schema->resultset('CD')->search(
564 'artist.name' => 'Bob Marley'
565 'liner_notes.notes' => { 'like', '%some text%' },
568 join => [qw/ artist liner_notes /],
569 order_by => [qw/ artist.name /],
574 # SELECT cd.*, artist.*, liner_notes.* FROM cd
575 # JOIN artist ON cd.artist = artist.id
576 # JOIN liner_notes ON cd.id = liner_notes.cd
577 # WHERE artist.name = 'Bob Marley'
578 # ORDER BY artist.name
580 =head2 Multi-step joins
582 Sometimes you want to join more than one relationship deep. In this example,
583 we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
584 contain a specific string:
586 # Relationships defined elsewhere:
587 # Artist->has_many('cds' => 'CD', 'artist');
588 # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
590 my $rs = $schema->resultset('Artist')->search(
592 'liner_notes.notes' => { 'like', '%some text%' },
596 'cds' => 'liner_notes'
602 # SELECT artist.* FROM artist
603 # LEFT JOIN cd ON artist.id = cd.artist
604 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
605 # WHERE liner_notes.notes LIKE '%some text%'
607 Joins can be nested to an arbitrary level. So if we decide later that we
608 want to reduce the number of Artists returned based on who wrote the liner
611 # Relationship defined elsewhere:
612 # LinerNotes->belongs_to('author' => 'Person');
614 my $rs = $schema->resultset('Artist')->search(
616 'liner_notes.notes' => { 'like', '%some text%' },
617 'author.name' => 'A. Writer'
622 'liner_notes' => 'author'
629 # SELECT artist.* FROM artist
630 # LEFT JOIN cd ON artist.id = cd.artist
631 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
632 # LEFT JOIN author ON author.id = liner_notes.author
633 # WHERE liner_notes.notes LIKE '%some text%'
634 # AND author.name = 'A. Writer'
636 =head2 Multi-step and multiple joins
638 With various combinations of array and hash references, you can join
639 tables in any combination you desire. For example, to join Artist to
640 CD and Concert, and join CD to LinerNotes:
642 # Relationships defined elsewhere:
643 # Artist->has_many('concerts' => 'Concert', 'artist');
645 my $rs = $schema->resultset('Artist')->search(
658 # SELECT artist.* FROM artist
659 # LEFT JOIN cd ON artist.id = cd.artist
660 # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
661 # LEFT JOIN concert ON artist.id = concert.artist
663 =head2 Multi-step prefetch
665 C<prefetch> can be nested more than one relationship
666 deep using the same syntax as a multi-step join:
668 my $rs = $schema->resultset('Tag')->search(
678 # SELECT tag.*, cd.*, artist.* FROM tag
679 # JOIN cd ON tag.cd = cd.id
680 # JOIN artist ON cd.artist = artist.id
682 Now accessing our C<cd> and C<artist> relationships does not need additional
685 my $tag = $rs->first;
686 print $tag->cd->artist->name;
688 =head1 ROW-LEVEL OPERATIONS
690 =head2 Retrieving a row object's Schema
692 It is possible to get a Schema object from a row object like so:
694 my $schema = $cd->result_source->schema;
695 # use the schema as normal:
696 my $artist_rs = $schema->resultset('Artist');
698 This can be useful when you don't want to pass around a Schema object to every
701 =head2 Getting the value of the primary key for the last database insert
703 AKA getting last_insert_id
705 Thanks to the core component PK::Auto, this is straightforward:
707 my $foo = $rs->create(\%blah);
709 my $id = $foo->id; # foo->my_primary_key_field will also work.
711 If you are not using autoincrementing primary keys, this will probably
712 not work, but then you already know the value of the last primary key anyway.
714 =head2 Stringification
716 Employ the standard stringification technique by using the L<overload>
719 To make an object stringify itself as a single column, use something
720 like this (replace C<name> with the column/method of your choice):
722 use overload '""' => sub { shift->name}, fallback => 1;
724 For more complex stringification, you can use an anonymous subroutine:
726 use overload '""' => sub { $_[0]->name . ", " .
727 $_[0]->address }, fallback => 1;
729 =head3 Stringification Example
731 Suppose we have two tables: C<Product> and C<Category>. The table
734 Product(id, Description, category)
735 Category(id, Description)
737 C<category> is a foreign key into the Category table.
739 If you have a Product object C<$obj> and write something like
743 things will not work as expected.
745 To obtain, for example, the category description, you should add this
746 method to the class defining the Category table:
748 use overload "" => sub {
751 return $self->Description;
754 =head2 Want to know if find_or_create found or created a row?
756 Just use C<find_or_new> instead, then check C<in_storage>:
758 my $obj = $rs->find_or_new({ blah => 'blarg' });
759 unless ($obj->in_storage) {
761 # do whatever else you wanted if it was a new row
764 =head2 Static sub-classing DBIx::Class result classes
766 AKA adding additional relationships/methods/etc. to a model for a
767 specific usage of the (shared) model.
771 package My::App::Schema;
773 use base DBIx::Class::Schema;
775 # load subclassed classes from My::App::Schema::Result/ResultSet
776 __PACKAGE__->load_namespaces;
778 # load classes from shared model
780 'My::Shared::Model::Result' => [qw/
787 B<Result-Subclass definition>
789 package My::App::Schema::Result::Baz;
793 use base My::Shared::Model::Result::Baz;
795 # WARNING: Make sure you call table() again in your subclass,
796 # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
797 # and the class name is not correctly registered as a source
798 __PACKAGE__->table('baz');
800 sub additional_method {
801 return "I'm an additional method only needed by this app";
806 =head2 Dynamic Sub-classing DBIx::Class proxy classes
808 AKA multi-class object inflation from one table
810 L<DBIx::Class> classes are proxy classes, therefore some different
811 techniques need to be employed for more than basic subclassing. In
812 this example we have a single user table that carries a boolean bit
813 for admin. We would like like to give the admin users
814 objects (L<DBIx::Class::Row>) the same methods as a regular user but
815 also special admin only methods. It doesn't make sense to create two
816 seperate proxy-class files for this. We would be copying all the user
817 methods into the Admin class. There is a cleaner way to accomplish
820 Overriding the C<inflate_result> method within the User proxy-class
821 gives us the effect we want. This method is called by
822 L<DBIx::Class::ResultSet> when inflating a result from storage. So we
823 grab the object being returned, inspect the values we are looking for,
824 bless it if it's an admin object, and then return it. See the example
831 use base qw/DBIx::Class::Schema/;
833 __PACKAGE__->load_namespaces;
838 B<Proxy-Class definitions>
840 package My::Schema::Result::User;
844 use base qw/DBIx::Class/;
846 ### Define what our admin class is, for ensure_class_loaded()
847 my $admin_class = __PACKAGE__ . '::Admin';
849 __PACKAGE__->load_components(qw/Core/);
851 __PACKAGE__->table('users');
853 __PACKAGE__->add_columns(qw/user_id email password
854 firstname lastname active
857 __PACKAGE__->set_primary_key('user_id');
861 my $ret = $self->next::method(@_);
862 if( $ret->admin ) {### If this is an admin, rebless for extra functions
863 $self->ensure_class_loaded( $admin_class );
864 bless $ret, $admin_class;
870 print "I am a regular user.\n";
877 package My::Schema::Result::User::Admin;
881 use base qw/My::Schema::Result::User/;
883 # This line is important
884 __PACKAGE__->table('users');
888 print "I am an admin.\n";
894 print "I am doing admin stuff\n";
906 my $user_data = { email => 'someguy@place.com',
910 my $admin_data = { email => 'someadmin@adminplace.com',
914 my $schema = My::Schema->connection('dbi:Pg:dbname=test');
916 $schema->resultset('User')->create( $user_data );
917 $schema->resultset('User')->create( $admin_data );
919 ### Now we search for them
920 my $user = $schema->resultset('User')->single( $user_data );
921 my $admin = $schema->resultset('User')->single( $admin_data );
923 print ref $user, "\n";
924 print ref $admin, "\n";
926 print $user->password , "\n"; # pass1
927 print $admin->password , "\n";# pass2; inherited from User
928 print $user->hello , "\n";# I am a regular user.
929 print $admin->hello, "\n";# I am an admin.
931 ### The statement below will NOT print
932 print "I can do admin stuff\n" if $user->can('do_admin_stuff');
933 ### The statement below will print
934 print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
936 Alternatively you can use L<DBIx::Class::DynamicSubclass> that implements
937 exactly the above functionality.
939 =head2 Skip row object creation for faster results
941 DBIx::Class is not built for speed, it's built for convenience and
942 ease of use, but sometimes you just need to get the data, and skip the
945 To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
947 my $rs = $schema->resultset('CD');
949 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
951 my $hash_ref = $rs->find(1);
955 Beware, changing the Result class using
956 L<DBIx::Class::ResultSet/result_class> will replace any existing class
957 completely including any special components loaded using
958 load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
960 =head2 Get raw data for blindingly fast results
962 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> solution
963 above is not fast enough for you, you can use a DBIx::Class to return values
964 exactly as they come out of the database with none of the convenience methods
967 This is used like so:
969 my $cursor = $rs->cursor
970 while (my @vals = $cursor->next) {
971 # use $val[0..n] here
974 You will need to map the array offsets to particular columns (you can
975 use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
977 =head1 RESULTSET OPERATIONS
979 =head2 Getting Schema from a ResultSet
981 To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
983 $rs->result_source->schema
985 =head2 Getting Columns Of Data
989 If you want to find the sum of a particular column there are several
990 ways, the obvious one is to use search:
992 my $rs = $schema->resultset('Items')->search(
995 select => [ { sum => 'Cost' } ],
996 as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
999 my $tc = $rs->first->get_column('total_cost');
1001 Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
1002 returned when you ask the C<ResultSet> for a column using
1005 my $cost = $schema->resultset('Items')->get_column('Cost');
1006 my $tc = $cost->sum;
1008 With this you can also do:
1010 my $minvalue = $cost->min;
1011 my $maxvalue = $cost->max;
1013 Or just iterate through the values of this column only:
1015 while ( my $c = $cost->next ) {
1019 foreach my $c ($cost->all) {
1023 C<ResultSetColumn> only has a limited number of built-in functions. If
1024 you need one that it doesn't have, then you can use the C<func> method
1027 my $avg = $cost->func('AVERAGE');
1029 This will cause the following SQL statement to be run:
1031 SELECT AVERAGE(Cost) FROM Items me
1033 Which will of course only work if your database supports this function.
1034 See L<DBIx::Class::ResultSetColumn> for more documentation.
1036 =head2 Creating a result set from a set of rows
1038 Sometimes you have a (set of) row objects that you want to put into a
1039 resultset without the need to hit the DB again. You can do that by using the
1040 L<set_cache|DBIx::Class::Resultset/set_cache> method:
1042 my @uploadable_groups;
1043 while (my $group = $groups->next) {
1044 if ($group->can_upload($self)) {
1045 push @uploadable_groups, $group;
1048 my $new_rs = $self->result_source->resultset;
1049 $new_rs->set_cache(\@uploadable_groups);
1053 =head1 USING RELATIONSHIPS
1055 =head2 Create a new row in a related table
1057 my $author = $book->create_related('author', { name => 'Fred'});
1059 =head2 Search in a related table
1061 Only searches for books named 'Titanic' by the author in $author.
1063 my $books_rs = $author->search_related('books', { name => 'Titanic' });
1065 =head2 Delete data in a related table
1067 Deletes only the book named Titanic by the author in $author.
1069 $author->delete_related('books', { name => 'Titanic' });
1071 =head2 Ordering a relationship result set
1073 If you always want a relation to be ordered, you can specify this when you
1074 create the relationship.
1076 To order C<< $book->pages >> by descending page_number, create the relation
1079 __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
1081 =head2 Filtering a relationship result set
1083 If you want to get a filtered result set, you can just add add to $attr as follows:
1085 __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1087 =head2 Many-to-many relationships
1089 This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
1092 use base 'DBIx::Class';
1093 __PACKAGE__->load_components('Core');
1094 __PACKAGE__->table('user');
1095 __PACKAGE__->add_columns(qw/id name/);
1096 __PACKAGE__->set_primary_key('id');
1097 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1098 __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1100 package My::UserAddress;
1101 use base 'DBIx::Class';
1102 __PACKAGE__->load_components('Core');
1103 __PACKAGE__->table('user_address');
1104 __PACKAGE__->add_columns(qw/user address/);
1105 __PACKAGE__->set_primary_key(qw/user address/);
1106 __PACKAGE__->belongs_to('user' => 'My::User');
1107 __PACKAGE__->belongs_to('address' => 'My::Address');
1109 package My::Address;
1110 use base 'DBIx::Class';
1111 __PACKAGE__->load_components('Core');
1112 __PACKAGE__->table('address');
1113 __PACKAGE__->add_columns(qw/id street town area_code country/);
1114 __PACKAGE__->set_primary_key('id');
1115 __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1116 __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1118 $rs = $user->addresses(); # get all addresses for a user
1119 $rs = $address->users(); # get all users for an address
1121 my $address = $user->add_to_addresses( # returns a My::Address instance,
1122 # NOT a My::UserAddress instance!
1124 country => 'United Kingdom',
1131 =head2 Relationships across DB schemas
1133 Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
1134 is easy as long as the schemas themselves are all accessible via the same DBI
1135 connection. In most cases, this means that they are on the same database host
1136 as each other and your connecting database user has the proper permissions to them.
1138 To accomplish this one only needs to specify the DB schema name in the table
1139 declaration, like so...
1141 package MyDatabase::Main::Artist;
1142 use base qw/DBIx::Class/;
1143 __PACKAGE__->load_components(qw/PK::Auto Core/);
1145 __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1147 __PACKAGE__->add_columns(qw/ artist_id name /);
1148 __PACKAGE__->set_primary_key('artist_id');
1149 __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
1153 Whatever string you specify there will be used to build the "FROM" clause in SQL
1156 The big drawback to this is you now have DB schema names hardcoded in your
1157 class files. This becomes especially troublesome if you have multiple instances
1158 of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
1159 the DB schemas are named based on the environment (e.g. database1_dev).
1161 However, one can dynamically "map" to the proper DB schema by overriding the
1162 L<connection|DBIx::Class::Schama/connection> method in your Schema class and
1163 building a renaming facility, like so:
1165 package MyDatabase::Schema;
1168 extends 'DBIx::Class::Schema';
1170 around connection => sub {
1171 my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1173 my $postfix = delete $attr->{schema_name_postfix};
1178 $self->append_db_name($postfix);
1182 sub append_db_name {
1183 my ( $self, $postfix ) = @_;
1187 { $_->name =~ /^\w+\./mx }
1189 { $self->source($_) }
1192 foreach my $source (@sources_with_db) {
1193 my $name = $source->name;
1194 $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1196 $source->name($name);
1202 By overridding the L<connection|DBIx::Class::Schama/connection>
1203 method and extracting a custom option from the provided \%attr hashref one can
1204 then simply iterate over all the Schema's ResultSources, renaming them as
1207 To use this facility, simply add or modify the \%attr hashref that is passed to
1208 L<connection|DBIx::Class::Schama/connect>, as follows:
1211 = MyDatabase::Schema->connect(
1216 schema_name_postfix => '_dev'
1217 # ... Other options as desired ...
1220 Obviously, one could accomplish even more advanced mapping via a hash map or a
1225 As of version 0.04001, there is improved transaction support in
1226 L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
1227 example of the recommended way to use it:
1229 my $genus = $schema->resultset('Genus')->find(12);
1231 my $coderef2 = sub {
1236 my $coderef1 = sub {
1237 $genus->add_to_species({ name => 'troglodyte' });
1240 $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1241 return $genus->species;
1246 $rs = $schema->txn_do($coderef1);
1249 if ($@) { # Transaction failed
1250 die "the sky is falling!" #
1251 if ($@ =~ /Rollback failed/); # Rollback failed
1253 deal_with_failed_transaction();
1256 Nested transactions will work as expected. That is, only the outermost
1257 transaction will actually issue a commit to the $dbh, and a rollback
1258 at any level of any transaction will cause the entire nested
1259 transaction to fail. Support for savepoints and for true nested
1260 transactions (for databases that support them) will hopefully be added
1265 =head2 Creating Schemas From An Existing Database
1267 L<DBIx::Class::Schema::Loader> will connect to a database and create a
1268 L<DBIx::Class::Schema> and associated sources by examining the database.
1270 The recommend way of achieving this is to use the
1271 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
1273 perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1274 -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
1276 This will create a tree of files rooted at C<./lib/My/Schema/> containing
1277 source definitions for all the tables found in the C<foo> database.
1279 =head2 Creating DDL SQL
1281 The following functionality requires you to have L<SQL::Translator>
1282 (also known as "SQL Fairy") installed.
1284 To create a set of database-specific .sql files for the above schema:
1286 my $schema = My::Schema->connect($dsn);
1287 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1292 By default this will create schema files in the current directory, for
1293 MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1295 To create a new database using the schema:
1297 my $schema = My::Schema->connect($dsn);
1298 $schema->deploy({ add_drop_tables => 1});
1300 To import created .sql files using the mysql client:
1302 mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1304 To create C<ALTER TABLE> conversion scripts to update a database to a
1305 newer version of your schema at a later point, first set a new
1306 C<$VERSION> in your Schema file, then:
1308 my $schema = My::Schema->connect($dsn);
1309 $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1315 This will produce new database-specific .sql files for the new version
1316 of the schema, plus scripts to convert from version 0.1 to 0.2. This
1317 requires that the files for 0.1 as created above are available in the
1318 given directory to diff against.
1320 =head2 Select from dual
1322 Dummy tables are needed by some databases to allow calling functions
1323 or expressions that aren't based on table content, for examples of how
1324 this applies to various database types, see:
1325 L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1327 Note: If you're using Oracles dual table don't B<ever> do anything
1328 other than a select, if you CRUD on your dual table you *will* break
1331 Make a table class as you would for any other table
1333 package MyAppDB::Dual;
1336 use base 'DBIx::Class';
1337 __PACKAGE__->load_components("Core");
1338 __PACKAGE__->table("Dual");
1339 __PACKAGE__->add_columns(
1341 { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1344 Once you've loaded your table class select from it using C<select>
1345 and C<as> instead of C<columns>
1347 my $rs = $schema->resultset('Dual')->search(undef,
1348 { select => [ 'sydate' ],
1353 All you have to do now is be careful how you access your resultset, the below
1354 will not work because there is no column called 'now' in the Dual table class
1356 while (my $dual = $rs->next) {
1357 print $dual->now."\n";
1359 # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1361 You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
1362 your Dual class for whatever you wanted to select from dual, but that's just
1363 silly, instead use C<get_column>
1365 while (my $dual = $rs->next) {
1366 print $dual->get_column('now')."\n";
1371 my $cursor = $rs->cursor;
1372 while (my @vals = $cursor->next) {
1373 print $vals[0]."\n";
1376 In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
1377 L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
1378 current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
1379 "sequence.nextval" anymore from dual. To avoid this problem, just tell
1380 L<SQL::Translator> to not create table dual:
1383 add_drop_table => 1,
1384 parser_args => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1386 $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1388 Or use L<DBIx::Class::ResultClass::HashRefInflator>
1390 $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1391 while ( my $dual = $rs->next ) {
1392 print $dual->{now}."\n";
1395 Here are some example C<select> conditions to illustrate the different syntax
1396 you could use for doing stuff like
1397 C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
1399 # get a sequence value
1400 select => [ 'A_SEQ.nextval' ],
1402 # get create table sql
1403 select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1405 # get a random num between 0 and 100
1406 select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1409 select => [ { 'extract' => [ \'year from sysdate' ] } ],
1412 select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1414 # which day of the week were you born on?
1415 select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1417 # select 16 rows from dual
1418 select => [ "'hello'" ],
1420 group_by => [ 'cube( 1, 2, 3, 4 )' ],
1424 =head2 Adding Indexes And Functions To Your SQL
1426 Often you will want indexes on columns on your table to speed up searching. To
1427 do this, create a method called C<sqlt_deploy_hook> in the relevant source
1428 class (refer to the advanced
1429 L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
1430 to share a hook between multiple sources):
1432 package My::Schema::Result::Artist;
1434 __PACKAGE__->table('artist');
1435 __PACKAGE__->add_columns(id => { ... }, name => { ... })
1437 sub sqlt_deploy_hook {
1438 my ($self, $sqlt_table) = @_;
1440 $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1445 Sometimes you might want to change the index depending on the type of the
1446 database for which SQL is being generated:
1448 my ($db_type = $sqlt_table->schema->translator->producer_type)
1449 =~ s/^SQL::Translator::Producer:://;
1451 You can also add hooks to the schema level to stop certain tables being
1458 sub sqlt_deploy_hook {
1459 my ($self, $sqlt_schema) = @_;
1461 $sqlt_schema->drop_table('table_name');
1464 You could also add views, procedures or triggers to the output using
1465 L<SQL::Translator::Schema/add_view>,
1466 L<SQL::Translator::Schema/add_procedure> or
1467 L<SQL::Translator::Schema/add_trigger>.
1470 =head2 Schema versioning
1472 The following example shows simplistically how you might use DBIx::Class to
1473 deploy versioned schemas to your customers. The basic process is as follows:
1479 Create a DBIx::Class schema
1491 Modify schema to change functionality
1495 Deploy update to customers
1499 B<Create a DBIx::Class schema>
1501 This can either be done manually, or generated from an existing database as
1502 described under L</Creating Schemas From An Existing Database>
1506 Call L<DBIx::Class::Schema/create_ddl_dir> as above under L</Creating DDL SQL>.
1508 B<Deploy to customers>
1510 There are several ways you could deploy your schema. These are probably
1511 beyond the scope of this recipe, but might include:
1517 Require customer to apply manually using their RDBMS.
1521 Package along with your app, making database dump/schema update/tests
1522 all part of your install.
1526 B<Modify the schema to change functionality>
1528 As your application evolves, it may be necessary to modify your schema
1529 to change functionality. Once the changes are made to your schema in
1530 DBIx::Class, export the modified schema and the conversion scripts as
1531 in L</Creating DDL SQL>.
1533 B<Deploy update to customers>
1535 Add the L<DBIx::Class::Schema::Versioned> schema component to your
1536 Schema class. This will add a new table to your database called
1537 C<dbix_class_schema_vesion> which will keep track of which version is installed
1538 and warn if the user trys to run a newer schema version than the
1539 database thinks it has.
1541 Alternatively, you can send the conversion sql scripts to your
1544 =head2 Setting quoting for the generated SQL
1546 If the database contains column names with spaces and/or reserved words, they
1547 need to be quoted in the SQL queries. This is done using:
1549 $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
1550 $schema->storage->sql_maker->name_sep('.');
1552 The first sets the quote characters. Either a pair of matching
1553 brackets, or a C<"> or C<'>:
1555 $schema->storage->sql_maker->quote_char('"');
1557 Check the documentation of your database for the correct quote
1558 characters to use. C<name_sep> needs to be set to allow the SQL
1559 generator to put the quotes the correct place.
1561 In most cases you should set these as part of the arguments passed to
1562 L<DBIx::Class::Schema/connect>:
1564 my $schema = My::Schema->connect(
1574 In some cases, quoting will be required for all users of a schema. To enforce
1575 this, you can also overload the C<connection> method for your schema class:
1579 my $rv = $self->next::method( @_ );
1580 $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
1581 $rv->storage->sql_maker->name_sep('.');
1585 =head2 Setting limit dialect for SQL::Abstract::Limit
1587 In some cases, SQL::Abstract::Limit cannot determine the dialect of
1588 the remote SQL server by looking at the database handle. This is a
1589 common problem when using the DBD::JDBC, since the DBD-driver only
1590 know that in has a Java-driver available, not which JDBC driver the
1591 Java component has loaded. This specifically sets the limit_dialect
1592 to Microsoft SQL-server (See more names in SQL::Abstract::Limit
1595 __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
1597 The JDBC bridge is one way of getting access to a MSSQL server from a platform
1598 that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
1600 The limit dialect can also be set at connect time by specifying a
1601 C<limit_dialect> key in the final hash as shown above.
1603 =head2 Working with PostgreSQL array types
1605 You can also assign values to PostgreSQL array columns by passing array
1606 references in the C<\%columns> (C<\%vals>) hashref of the
1607 L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
1610 $resultset->create({
1611 numbers => [1, 2, 3]
1616 numbers => [1, 2, 3]
1623 In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
1624 methods) you cannot directly use array references (since this is interpreted as
1625 a list of values to be C<OR>ed), but you can use the following syntax to force
1626 passing them as bind values:
1630 numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1634 See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
1635 placeholders and bind values (subqueries)> for more explanation. Note that
1636 L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
1637 the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
1638 arrayrefs together with the column name, like this: C<< [column_name => value]
1641 =head1 BOOTSTRAPPING/MIGRATING
1643 =head2 Easy migration from class-based to schema-based setup
1645 You want to start using the schema-based approach to L<DBIx::Class>
1646 (see L<SchemaIntro.pod>), but have an established class-based setup with lots
1647 of existing classes that you don't want to move by hand. Try this nifty script
1651 use SQL::Translator;
1653 my $schema = MyDB->schema_instance;
1655 my $translator = SQL::Translator->new(
1656 debug => $debug || 0,
1657 trace => $trace || 0,
1658 no_comments => $no_comments || 0,
1659 show_warnings => $show_warnings || 0,
1660 add_drop_table => $add_drop_table || 0,
1661 validate => $validate || 0,
1663 'DBIx::Schema' => $schema,
1666 'prefix' => 'My::Schema',
1670 $translator->parser('SQL::Translator::Parser::DBIx::Class');
1671 $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1673 my $output = $translator->translate(@args) or die
1674 "Error: " . $translator->error;
1678 You could use L<Module::Find> to search for all subclasses in the MyDB::*
1679 namespace, which is currently left as an exercise for the reader.
1681 =head1 OVERLOADING METHODS
1683 L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of
1684 method calls, useful for things like default values and triggers. You have to
1685 use calls to C<next::method> to overload methods. More information on using
1686 L<Class::C3> with L<DBIx::Class> can be found in
1687 L<DBIx::Class::Manual::Component>.
1689 =head2 Setting default values for a row
1691 It's as simple as overriding the C<new> method. Note the use of
1695 my ( $class, $attrs ) = @_;
1697 $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1699 my $new = $class->next::method($attrs);
1704 For more information about C<next::method>, look in the L<Class::C3>
1705 documentation. See also L<DBIx::Class::Manual::Component> for more
1706 ways to write your own base classes to do this.
1708 People looking for ways to do "triggers" with DBIx::Class are probably
1709 just looking for this.
1711 =head2 Changing one field whenever another changes
1713 For example, say that you have three columns, C<id>, C<number>, and
1714 C<squared>. You would like to make changes to C<number> and have
1715 C<squared> be automagically set to the value of C<number> squared.
1716 You can accomplish this by overriding C<store_column>:
1719 my ( $self, $name, $value ) = @_;
1720 if ($name eq 'number') {
1721 $self->squared($value * $value);
1723 $self->next::method($name, $value);
1726 Note that the hard work is done by the call to C<next::method>, which
1727 redispatches your call to store_column in the superclass(es).
1729 =head2 Automatically creating related objects
1731 You might have a class C<Artist> which has many C<CD>s. Further, you
1732 want to create a C<CD> object every time you insert an C<Artist> object.
1733 You can accomplish this by overriding C<insert> on your objects:
1736 my ( $self, @args ) = @_;
1737 $self->next::method(@args);
1738 $self->cds->new({})->fill_from_artist($self)->insert;
1742 where C<fill_from_artist> is a method you specify in C<CD> which sets
1743 values in C<CD> based on the data in the C<Artist> object you pass in.
1745 =head2 Wrapping/overloading a column accessor
1749 Say you have a table "Camera" and want to associate a description
1750 with each camera. For most cameras, you'll be able to generate the description from
1751 the other columns. However, in a few special cases you may want to associate a
1752 custom description with a camera.
1756 In your database schema, define a description field in the "Camera" table that
1757 can contain text and null values.
1759 In DBIC, we'll overload the column accessor to provide a sane default if no
1760 custom description is defined. The accessor will either return or generate the
1761 description, depending on whether the field is null or not.
1763 First, in your "Camera" schema class, define the description field as follows:
1765 __PACKAGE__->add_columns(description => { accessor => '_description' });
1767 Next, we'll define the accessor-wrapper subroutine:
1772 # If there is an update to the column, we'll let the original accessor
1774 return $self->_description(@_) if @_;
1776 # Fetch the column value.
1777 my $description = $self->_description;
1779 # If there's something in the description field, then just return that.
1780 return $description if defined $description && length $descripton;
1782 # Otherwise, generate a description.
1783 return $self->generate_description;
1786 =head1 DEBUGGING AND PROFILING
1788 =head2 DBIx::Class objects with Data::Dumper
1790 L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
1791 be hard to find the pertinent data in all the data it can generate.
1792 Specifically, if one naively tries to use it like so,
1796 my $cd = $schema->resultset('CD')->find(1);
1799 several pages worth of data from the CD object's schema and result source will
1800 be dumped to the screen. Since usually one is only interested in a few column
1801 values of the object, this is not very helpful.
1803 Luckily, it is possible to modify the data before L<Data::Dumper> outputs
1804 it. Simply define a hook that L<Data::Dumper> will call on the object before
1805 dumping it. For example,
1812 result_source => undef,
1820 local $Data::Dumper::Freezer = '_dumper_hook';
1822 my $cd = $schema->resultset('CD')->find(1);
1824 # dumps $cd without its ResultSource
1826 If the structure of your schema is such that there is a common base class for
1827 all your table classes, simply put a method similar to C<_dumper_hook> in the
1828 base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
1829 will automagically clean up your data before printing it. See
1830 L<Data::Dumper/EXAMPLES> for more information.
1834 When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
1835 executed as well as notifications of query completion and transaction
1836 begin/commit. If you'd like to profile the SQL you can subclass the
1837 L<DBIx::Class::Storage::Statistics> class and write your own profiling
1840 package My::Profiler;
1843 use base 'DBIx::Class::Storage::Statistics';
1845 use Time::HiRes qw(time);
1854 $self->print("Executing $sql: ".join(', ', @params)."\n");
1863 my $elapsed = sprintf("%0.4f", time() - $start);
1864 $self->print("Execution took $elapsed seconds.\n");
1870 You can then install that class as the debugging object:
1872 __PACKAGE__->storage->debugobj(new My::Profiler());
1873 __PACKAGE__->storage->debug(1);
1875 A more complicated example might involve storing each execution of SQL in an
1883 my $elapsed = time() - $start;
1884 push(@{ $calls{$sql} }, {
1890 You could then create average, high and low execution times for an SQL
1891 statement and dig down to see if certain parameters cause aberrant behavior.
1892 You might want to check out L<DBIx::Class::QueryLog> as well.
1894 =head1 STARTUP SPEED
1896 L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
1897 as the ORM loads all the relevant classes. This section examines
1898 techniques for reducing the startup delay.
1900 These tips are are listed in order of decreasing effectiveness - so the
1901 first tip, if applicable, should have the greatest effect on your
1904 =head2 Statically Define Your Schema
1907 L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
1908 classes dynamically based on the database schema then there will be a
1909 significant startup delay.
1911 For production use a statically defined schema (which can be generated
1912 using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
1913 the database schema once - see
1914 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
1915 L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
1916 details on creating static schemas from a database).
1918 =head2 Move Common Startup into a Base Class
1920 Typically L<DBIx::Class> result classes start off with
1922 use base qw/DBIx::Class/;
1923 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1925 If this preamble is moved into a common base class:-
1929 use base qw/DBIx::Class/;
1930 __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
1933 and each result class then uses this as a base:-
1935 use base qw/MyDBICbase/;
1937 then the load_components is only performed once, which can result in a
1938 considerable startup speedup for schemas with many classes.
1940 =head2 Explicitly List Schema Result Classes
1942 The schema class will normally contain
1944 __PACKAGE__->load_classes();
1946 to load the result classes. This will use L<Module::Find|Module::Find>
1947 to find and load the appropriate modules. Explicitly defining the
1948 classes you wish to load will remove the overhead of
1949 L<Module::Find|Module::Find> and the related directory operations:
1951 __PACKAGE__->load_classes(qw/ CD Artist Track /);
1953 If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
1954 syntax to load the appropriate classes there is not a direct alternative
1955 avoiding L<Module::Find|Module::Find>.
1959 =head2 Cached statements
1961 L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
1962 This is normally a good idea, but if too many statements are cached, the database may use too much
1963 memory and may eventually run out and fail entirely. If you suspect this may be the case, you may want
1964 to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
1966 # print all currently cached prepared statements
1967 print for keys %{$schema->storage->dbh->{CachedKids}};
1968 # get a count of currently cached prepared statements
1969 my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
1971 If it's appropriate, you can simply clear these statements, automatically deallocating them in the
1974 my $kids = $schema->storage->dbh->{CachedKids};
1975 delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
1977 But what you probably want is to expire unused statements and not those that are used frequently.
1978 You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
1982 my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
1983 on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },