1DBIx::Class::Manual::CoUoskebrooCko(n3t)ributed Perl DocDuBmIexn:t:aCtliaosns::Manual::Cookbook(3)
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NAME

6       DBIx::Class::Manual::Cookbook - Miscellaneous recipes
7

SEARCHING

9   Paged results
10       When you expect a large number of results, you can ask DBIx::Class for
11       a paged resultset, which will fetch only a defined number of records at
12       a time:
13
14         my $rs = $schema->resultset('Artist')->search(
15           undef,
16           {
17             page => 1,  # page to return (defaults to 1)
18             rows => 10, # number of results per page
19           },
20         );
21
22         return $rs->all(); # all records for page 1
23
24         return $rs->page(2); # records for page 2
25
26       You can get a Data::Page object for the resultset (suitable for use in
27       e.g. a template) using the "pager" method:
28
29         return $rs->pager();
30
31   Complex WHERE clauses
32       Sometimes you need to formulate a query using specific operators:
33
34         my @albums = $schema->resultset('Album')->search({
35           artist => { 'like', '%Lamb%' },
36           title  => { 'like', '%Fear of Fours%' },
37         });
38
39       This results in something like the following "WHERE" clause:
40
41         WHERE artist LIKE ? AND title LIKE ?
42
43       And the following bind values for the placeholders: '%Lamb%', '%Fear of
44       Fours%'.
45
46       Other queries might require slightly more complex logic:
47
48         my @albums = $schema->resultset('Album')->search({
49           -or => [
50             -and => [
51               artist => { 'like', '%Smashing Pumpkins%' },
52               title  => 'Siamese Dream',
53             ],
54             artist => 'Starchildren',
55           ],
56         });
57
58       This results in the following "WHERE" clause:
59
60         WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
61           OR artist = 'Starchildren'
62
63       For more information on generating complex queries, see "WHERE CLAUSES"
64       in SQL::Abstract.
65
66   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 $rs->first, it is suboptimal, as a full blown
69       cursor for the resultset will be created and then immediately destroyed
70       after fetching the first row object.  $rs->single is designed
71       specifically for this case - it will grab the first returned result
72       without even instantiating a cursor.
73
74       Before replacing all your calls to "first()" with "single()" please
75       observe the following CAVEATS:
76
77       ·   While single() takes a search condition just like search() does, it
78           does _not_ accept search attributes. However one can always chain a
79           single() to a search():
80
81             my $top_cd = $cd_rs->search({}, { order_by => 'rating' })->single;
82
83       ·   Since single() is the engine behind find(), it is designed to fetch
84           a single row per database query. Thus a warning will be issued when
85           the underlying SELECT returns more than one row. Sometimes however
86           this usage is valid: i.e. we have an arbitrary number of cd's but
87           only one of them is at the top of the charts at any given time. If
88           you know what you are doing, you can silence the warning by
89           explicitly limiting the resultset size:
90
91             my $top_cd = $cd_rs->search ({}, { order_by => 'rating', rows => 1 })->single;
92
93   Arbitrary SQL through a custom ResultSource
94       Sometimes you have to run arbitrary SQL because your query is too
95       complex (e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.)
96       or has to be optimized for your database in a special way, but you
97       still want to get the results as a DBIx::Class::ResultSet.
98
99       This is accomplished by defining a ResultSource::View for your query,
100       almost like you would define a regular ResultSource.
101
102         package My::Schema::Result::UserFriendsComplex;
103         use strict;
104         use warnings;
105         use base qw/DBIx::Class::Core/;
106
107         __PACKAGE__->table_class('DBIx::Class::ResultSource::View');
108
109         # For the time being this is necessary even for virtual views
110         __PACKAGE__->table($view_name);
111
112         #
113         # ->add_columns, etc.
114         #
115
116         # do not attempt to deploy() this view
117         __PACKAGE__->result_source_instance->is_virtual(1);
118
119         __PACKAGE__->result_source_instance->view_definition(q[
120           SELECT u.* FROM user u
121           INNER JOIN user_friends f ON u.id = f.user_id
122           WHERE f.friend_user_id = ?
123           UNION
124           SELECT u.* FROM user u
125           INNER JOIN user_friends f ON u.id = f.friend_user_id
126           WHERE f.user_id = ?
127         ]);
128
129       Next, you can execute your complex query using bind parameters like
130       this:
131
132         my $friends = $schema->resultset( 'UserFriendsComplex' )->search( {},
133           {
134             bind  => [ 12345, 12345 ]
135           }
136         );
137
138       ... and you'll get back a perfect DBIx::Class::ResultSet (except, of
139       course, that you cannot modify the rows it contains, e.g. cannot call
140       update or delete on it).
141
142       Note that you cannot have bind parameters unless is_virtual is set to
143       true.
144
145       ·   NOTE
146
147           If you're using the old deprecated "$rsrc_instance->name(\'( SELECT
148           ...')" method for custom SQL execution, you are highly encouraged
149           to update your code to use a virtual view as above. If you do not
150           want to change your code, and just want to suppress the deprecation
151           warning when you call "deploy" in DBIx::Class::Schema, add this
152           line to your source definition, so that "deploy" will exclude this
153           "table":
154
155             sub sqlt_deploy_hook { $_[1]->schema->drop_table ($_[1]) }
156
157   Using specific columns
158       When you only want specific columns from a table, you can use "columns"
159       to specify which ones you need. This is useful to avoid loading columns
160       with large amounts of data that you aren't about to use anyway:
161
162         my $rs = $schema->resultset('Artist')->search(
163           undef,
164           {
165             columns => [qw/ name /]
166           }
167         );
168
169         # Equivalent SQL:
170         # SELECT artist.name FROM artist
171
172       This is a shortcut for "select" and "as", see below. "columns" cannot
173       be used together with "select" and "as".
174
175   Using database functions or stored procedures
176       The combination of "select" and "as" can be used to return the result
177       of a database function or stored procedure as a column value. You use
178       "select" to specify the source for your column value (e.g. a column
179       name, function, or stored procedure name). You then use "as" to set the
180       column name you will use to access the returned value:
181
182         my $rs = $schema->resultset('Artist')->search(
183           {},
184           {
185             select => [ 'name', { LENGTH => 'name' } ],
186             as     => [qw/ name name_length /],
187           }
188         );
189
190         # Equivalent SQL:
191         # SELECT name name, LENGTH( name )
192         # FROM artist
193
194       Note that the "as" attribute has absolutely nothing to do with the SQL
195       syntax " SELECT foo AS bar " (see the documentation in "ATTRIBUTES" in
196       DBIx::Class::ResultSet). You can control the "AS" part of the generated
197       SQL via the "-as" field attribute as follows:
198
199         my $rs = $schema->resultset('Artist')->search(
200           {},
201           {
202             join => 'cds',
203             distinct => 1,
204             '+select' => [ { count => 'cds.cdid', -as => 'amount_of_cds' } ],
205             '+as' => [qw/num_cds/],
206             order_by => { -desc => 'amount_of_cds' },
207           }
208         );
209
210         # Equivalent SQL
211         # SELECT me.artistid, me.name, me.rank, me.charfield, COUNT( cds.cdid ) AS amount_of_cds
212         #   FROM artist me LEFT JOIN cd cds ON cds.artist = me.artistid
213         # GROUP BY me.artistid, me.name, me.rank, me.charfield
214         # ORDER BY amount_of_cds DESC
215
216       If your alias exists as a column in your base class (i.e. it was added
217       with add_columns), you just access it as normal. Our "Artist" class has
218       a "name" column, so we just use the "name" accessor:
219
220         my $artist = $rs->first();
221         my $name = $artist->name();
222
223       If on the other hand the alias does not correspond to an existing
224       column, you have to fetch the value using the "get_column" accessor:
225
226         my $name_length = $artist->get_column('name_length');
227
228       If you don't like using "get_column", you can always create an accessor
229       for any of your aliases using either of these:
230
231         # Define accessor manually:
232         sub name_length { shift->get_column('name_length'); }
233
234         # Or use DBIx::Class::AccessorGroup:
235         __PACKAGE__->mk_group_accessors('column' => 'name_length');
236
237       See also "Using SQL functions on the left hand side of a comparison".
238
239   SELECT DISTINCT with multiple columns
240         my $rs = $schema->resultset('Artist')->search(
241           {},
242           {
243             columns => [ qw/artist_id name rank/ ],
244             distinct => 1
245           }
246         );
247
248         my $rs = $schema->resultset('Artist')->search(
249           {},
250           {
251             columns => [ qw/artist_id name rank/ ],
252             group_by => [ qw/artist_id name rank/ ],
253           }
254         );
255
256         # Equivalent SQL:
257         # SELECT me.artist_id, me.name, me.rank
258         # FROM artist me
259         # GROUP BY artist_id, name, rank
260
261   SELECT COUNT(DISTINCT colname)
262         my $rs = $schema->resultset('Artist')->search(
263           {},
264           {
265             columns => [ qw/name/ ],
266             distinct => 1
267           }
268         );
269
270         my $rs = $schema->resultset('Artist')->search(
271           {},
272           {
273             columns => [ qw/name/ ],
274             group_by => [ qw/name/ ],
275           }
276         );
277
278         my $count = $rs->count;
279
280         # Equivalent SQL:
281         # SELECT COUNT( * ) FROM (SELECT me.name FROM artist me GROUP BY me.name) me:
282
283   Grouping results
284       DBIx::Class supports "GROUP BY" as follows:
285
286         my $rs = $schema->resultset('Artist')->search(
287           {},
288           {
289             join     => [qw/ cds /],
290             select   => [ 'name', { count => 'cds.id' } ],
291             as       => [qw/ name cd_count /],
292             group_by => [qw/ name /]
293           }
294         );
295
296         # Equivalent SQL:
297         # SELECT name, COUNT( cd.id ) FROM artist
298         # LEFT JOIN cd ON artist.id = cd.artist
299         # GROUP BY name
300
301       Please see "ATTRIBUTES" in DBIx::Class::ResultSet documentation if you
302       are in any way unsure about the use of the attributes above (" join ",
303       " select ", " as " and " group_by ").
304
305   Subqueries
306       You can write subqueries relatively easily in DBIC.
307
308         my $inside_rs = $schema->resultset('Artist')->search({
309           name => [ 'Billy Joel', 'Brittany Spears' ],
310         });
311
312         my $rs = $schema->resultset('CD')->search({
313           artist_id => { -in => $inside_rs->get_column('id')->as_query },
314         });
315
316       The usual operators ( '=', '!=', -in, -not_in, etc.) are supported.
317
318       NOTE: You have to explicitly use '=' when doing an equality comparison.
319       The following will not work:
320
321         my $rs = $schema->resultset('CD')->search({
322           artist_id => $inside_rs->get_column('id')->as_query,  # does NOT work
323         });
324
325       Support
326
327       Subqueries are supported in the where clause (first hashref), and in
328       the from, select, and +select attributes.
329
330       Correlated subqueries
331
332         my $cdrs = $schema->resultset('CD');
333         my $rs = $cdrs->search({
334           year => {
335             '=' => $cdrs->search(
336               { artist_id => { -ident => 'me.artist_id' } },
337               { alias => 'sub_query' }
338             )->get_column('year')->max_rs->as_query,
339           },
340         });
341
342       That creates the following SQL:
343
344         SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
345           FROM cd me
346         WHERE year = (
347           SELECT MAX(sub_query.year)
348             FROM cd sub_query
349           WHERE artist_id = me.artist_id
350         )
351
352   Predefined searches
353       You can define frequently used searches as methods by subclassing
354       DBIx::Class::ResultSet:
355
356         package My::DBIC::ResultSet::CD;
357         use strict;
358         use warnings;
359         use base 'DBIx::Class::ResultSet';
360
361         sub search_cds_ordered {
362             my ($self) = @_;
363
364             return $self->search(
365                 {},
366                 { order_by => 'name DESC' },
367             );
368         }
369
370         1;
371
372       If you're using "load_namespaces" in DBIx::Class::Schema, simply place
373       the file into the "ResultSet" directory next to your "Result"
374       directory, and it will be automatically loaded.
375
376       If however you are still using "load_classes" in DBIx::Class::Schema,
377       first tell DBIx::Class to create an instance of the ResultSet class for
378       you, in your My::DBIC::Schema::CD class:
379
380         # class definition as normal
381         use base 'DBIx::Class::Core';
382         __PACKAGE__->table('cd');
383
384         # tell DBIC to use the custom ResultSet class
385         __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
386
387       Note that "resultset_class" must be called after "load_components" and
388       "table", or you will get errors about missing methods.
389
390       Then call your new method in your code:
391
392          my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
393
394   Using SQL functions on the left hand side of a comparison
395       Using SQL functions on the left hand side of a comparison is generally
396       not a good idea since it requires a scan of the entire table. (Unless
397       your RDBMS supports indexes on expressions - including return values of
398       functions - and you create an index on the return value of the function
399       in question.) However, it can be accomplished with "DBIx::Class" when
400       necessary by resorting to literal SQL:
401
402         $rs->search(
403           \[ 'YEAR(date_of_birth) = ?', 1979 ]
404         );
405
406         # Equivalent SQL:
407         # SELECT * FROM employee WHERE YEAR(date_of_birth) = ?
408
409       To include the function as part of a larger search, use the '-and'
410       keyword to collect the search conditions:
411
412         $rs->search({ -and => [
413           name => 'Bob',
414           \[ 'YEAR(date_of_birth) = ?', 1979 ]
415         ]});
416
417         # Equivalent SQL:
418         # SELECT * FROM employee WHERE name = ? AND YEAR(date_of_birth) = ?
419
420       Note: the syntax for specifying the bind value's datatype and value is
421       explained in "DBIC BIND VALUES" in DBIx::Class::ResultSet.
422
423       See also "Literal SQL with placeholders and bind values (subqueries)"
424       in SQL::Abstract.
425
426   Software Limits
427       When your RDBMS does not have a working SQL limit mechanism (e.g.
428       Sybase ASE) and GenericSubQ is either too slow or does not work at all,
429       you can try the software_limit DBIx::Class::ResultSet attribute, which
430       skips over records to simulate limits in the Perl layer.
431
432       For example:
433
434         my $paged_rs = $rs->search({}, {
435           rows => 25,
436           page => 3,
437           order_by => [ 'me.last_name' ],
438           software_limit => 1,
439         });
440
441       You can set it as a default for your schema by placing the following in
442       your "Schema.pm":
443
444         __PACKAGE__->default_resultset_attributes({ software_limit => 1 });
445
446       WARNING: If you are dealing with large resultsets and your DBI or
447       ODBC/ADO driver does not have proper cursor support (i.e. it loads the
448       whole resultset into memory) then this feature will be extremely slow
449       and use huge amounts of memory at best, and may cause your process to
450       run out of memory and cause instability on your server at worst,
451       beware!
452

JOINS AND PREFETCHING

454   Using joins and prefetch
455       You can use the "join" attribute to allow searching on, or sorting your
456       results by, one or more columns in a related table.
457
458       This requires that you have defined the DBIx::Class::Relationship. For
459       example :
460
461         My::Schema::CD->has_many( artists => 'My::Schema::Artist', 'artist_id');
462
463       To return all CDs matching a particular artist name, you specify the
464       name of the relationship ('artists'):
465
466         my $rs = $schema->resultset('CD')->search(
467           {
468             'artists.name' => 'Bob Marley'
469           },
470           {
471             join => 'artists', # join the artist table
472           }
473         );
474
475         # Equivalent SQL:
476         # SELECT cd.* FROM cd
477         # JOIN artist ON cd.artist = artist.id
478         # WHERE artist.name = 'Bob Marley'
479
480       In that example both the join, and the condition use the relationship
481       name rather than the table name (see DBIx::Class::Manual::Joining for
482       more details on aliasing ).
483
484       If required, you can now sort on any column in the related tables by
485       including it in your "order_by" attribute, (again using the aliased
486       relation name rather than table name) :
487
488         my $rs = $schema->resultset('CD')->search(
489           {
490             'artists.name' => 'Bob Marley'
491           },
492           {
493             join     => 'artists',
494             order_by => [qw/ artists.name /]
495           }
496         );
497
498         # Equivalent SQL:
499         # SELECT cd.* FROM cd
500         # JOIN artist ON cd.artist = artist.id
501         # WHERE artist.name = 'Bob Marley'
502         # ORDER BY artist.name
503
504       Note that the "join" attribute should only be used when you need to
505       search or sort using columns in a related table. Joining related tables
506       when you only need columns from the main table will make performance
507       worse!
508
509       Now let's say you want to display a list of CDs, each with the name of
510       the artist. The following will work fine:
511
512         while (my $cd = $rs->next) {
513           print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
514         }
515
516       There is a problem however. We have searched both the "cd" and "artist"
517       tables in our main query, but we have only returned data from the "cd"
518       table. To get the artist name for any of the CD objects returned,
519       DBIx::Class will go back to the database:
520
521         SELECT artist.* FROM artist WHERE artist.id = ?
522
523       A statement like the one above will run for each and every CD returned
524       by our main query. Five CDs, five extra queries. A hundred CDs, one
525       hundred extra queries!
526
527       Thankfully, DBIx::Class has a "prefetch" attribute to solve this
528       problem.  This allows you to fetch results from related tables in
529       advance:
530
531         my $rs = $schema->resultset('CD')->search(
532           {
533             'artists.name' => 'Bob Marley'
534           },
535           {
536             join     => 'artists',
537             order_by => [qw/ artists.name /],
538             prefetch => 'artists' # return artist data too!
539           }
540         );
541
542         # Equivalent SQL (note SELECT from both "cd" and "artist"):
543         # SELECT cd.*, artist.* FROM cd
544         # JOIN artist ON cd.artist = artist.id
545         # WHERE artist.name = 'Bob Marley'
546         # ORDER BY artist.name
547
548       The code to print the CD list remains the same:
549
550         while (my $cd = $rs->next) {
551           print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
552         }
553
554       DBIx::Class has now prefetched all matching data from the "artist"
555       table, so no additional SQL statements are executed. You now have a
556       much more efficient query.
557
558       Also note that "prefetch" should only be used when you know you will
559       definitely use data from a related table. Pre-fetching related tables
560       when you only need columns from the main table will make performance
561       worse!
562
563   Multiple joins
564       In the examples above, the "join" attribute was a scalar.  If you pass
565       an array reference instead, you can join to multiple tables.  In this
566       example, we want to limit the search further, using "LinerNotes":
567
568         # Relationships defined elsewhere:
569         # CD->belongs_to('artist' => 'Artist');
570         # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
571         my $rs = $schema->resultset('CD')->search(
572           {
573             'artist.name' => 'Bob Marley'
574             'liner_notes.notes' => { 'like', '%some text%' },
575           },
576           {
577             join     => [qw/ artist liner_notes /],
578             order_by => [qw/ artist.name /],
579           }
580         );
581
582         # Equivalent SQL:
583         # SELECT cd.*, artist.*, liner_notes.* FROM cd
584         # JOIN artist ON cd.artist = artist.id
585         # JOIN liner_notes ON cd.id = liner_notes.cd
586         # WHERE artist.name = 'Bob Marley' AND liner_notes.notes LIKE '%some text%'
587         # ORDER BY artist.name
588
589   Multi-step joins
590       Sometimes you want to join more than one relationship deep. In this
591       example, we want to find all "Artist" objects who have "CD"s whose
592       "LinerNotes" contain a specific string:
593
594         # Relationships defined elsewhere:
595         # Artist->has_many('cds' => 'CD', 'artist');
596         # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
597
598         my $rs = $schema->resultset('Artist')->search(
599           {
600             'liner_notes.notes' => { 'like', '%some text%' },
601           },
602           {
603             join => {
604               'cds' => 'liner_notes'
605             }
606           }
607         );
608
609         # Equivalent SQL:
610         # SELECT artist.* FROM artist
611         # LEFT JOIN cd ON artist.id = cd.artist
612         # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
613         # WHERE liner_notes.notes LIKE '%some text%'
614
615       Joins can be nested to an arbitrary level. So if we decide later that
616       we want to reduce the number of Artists returned based on who wrote the
617       liner notes:
618
619         # Relationship defined elsewhere:
620         # LinerNotes->belongs_to('author' => 'Person');
621
622         my $rs = $schema->resultset('Artist')->search(
623           {
624             'liner_notes.notes' => { 'like', '%some text%' },
625             'author.name' => 'A. Writer'
626           },
627           {
628             join => {
629               'cds' => {
630                 'liner_notes' => 'author'
631               }
632             }
633           }
634         );
635
636         # Equivalent SQL:
637         # SELECT artist.* FROM artist
638         # LEFT JOIN cd ON artist.id = cd.artist
639         # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
640         # LEFT JOIN author ON author.id = liner_notes.author
641         # WHERE liner_notes.notes LIKE '%some text%'
642         # AND author.name = 'A. Writer'
643
644   Multi-step and multiple joins
645       With various combinations of array and hash references, you can join
646       tables in any combination you desire.  For example, to join Artist to
647       CD and Concert, and join CD to LinerNotes:
648
649         # Relationships defined elsewhere:
650         # Artist->has_many('concerts' => 'Concert', 'artist');
651
652         my $rs = $schema->resultset('Artist')->search(
653           { },
654           {
655             join => [
656               {
657                 cds => 'liner_notes'
658               },
659               'concerts'
660             ],
661           }
662         );
663
664         # Equivalent SQL:
665         # SELECT artist.* FROM artist
666         # LEFT JOIN cd ON artist.id = cd.artist
667         # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
668         # LEFT JOIN concert ON artist.id = concert.artist
669
670   Multi-step prefetch
671       "prefetch" can be nested more than one relationship deep using the same
672       syntax as a multi-step join:
673
674         my $rs = $schema->resultset('Tag')->search(
675           {},
676           {
677             prefetch => {
678               cd => 'artist'
679             }
680           }
681         );
682
683         # Equivalent SQL:
684         # SELECT tag.*, cd.*, artist.* FROM tag
685         # JOIN cd ON tag.cd = cd.id
686         # JOIN artist ON cd.artist = artist.id
687
688       Now accessing our "cd" and "artist" relationships does not need
689       additional SQL statements:
690
691         my $tag = $rs->first;
692         print $tag->cd->artist->name;
693

ROW-LEVEL OPERATIONS

695   Retrieving a result object's Schema
696       It is possible to get a Schema object from a result object like so:
697
698         my $schema = $cd->result_source->schema;
699         # use the schema as normal:
700         my $artist_rs = $schema->resultset('Artist');
701
702       This can be useful when you don't want to pass around a Schema object
703       to every method.
704
705   Getting the value of the primary key for the last database insert
706       AKA getting last_insert_id
707
708       Thanks to the core component PK::Auto, this is straightforward:
709
710         my $foo = $rs->create(\%blah);
711         # do more stuff
712         my $id = $foo->id; # foo->my_primary_key_field will also work.
713
714       If you are not using autoincrementing primary keys, this will probably
715       not work, but then you already know the value of the last primary key
716       anyway.
717
718   Stringification
719       Employ the standard stringification technique by using the overload
720       module.
721
722       To make an object stringify itself as a single column, use something
723       like this (replace "name" with the column/method of your choice):
724
725         use overload '""' => sub { shift->name}, fallback => 1;
726
727       For more complex stringification, you can use an anonymous subroutine:
728
729         use overload '""' => sub { $_[0]->name . ", " .
730                                    $_[0]->address }, fallback => 1;
731
732       Stringification Example
733
734       Suppose we have two tables: "Product" and "Category". The table
735       specifications are:
736
737         Product(id, Description, category)
738         Category(id, Description)
739
740       "category" is a foreign key into the Category table.
741
742       If you have a Product object $obj and write something like
743
744         print $obj->category
745
746       things will not work as expected.
747
748       To obtain, for example, the category description, you should add this
749       method to the class defining the Category table:
750
751         use overload "" => sub {
752             my $self = shift;
753
754             return $self->Description;
755         }, fallback => 1;
756
757   Want to know if find_or_create found or created a row?
758       Just use "find_or_new" instead, then check "in_storage":
759
760         my $obj = $rs->find_or_new({ blah => 'blarg' });
761         unless ($obj->in_storage) {
762           $obj->insert;
763           # do whatever else you wanted if it was a new row
764         }
765
766   Static sub-classing DBIx::Class result classes
767       AKA adding additional relationships/methods/etc. to a model for a
768       specific usage of the (shared) model.
769
770       Schema definition
771
772           package My::App::Schema;
773
774           use base 'DBIx::Class::Schema';
775
776           # load subclassed classes from My::App::Schema::Result/ResultSet
777           __PACKAGE__->load_namespaces;
778
779           # load classes from shared model
780           load_classes({
781               'My::Shared::Model::Result' => [qw/
782                   Foo
783                   Bar
784               /]});
785
786           1;
787
788       Result-Subclass definition
789
790           package My::App::Schema::Result::Baz;
791
792           use strict;
793           use warnings;
794           use base 'My::Shared::Model::Result::Baz';
795
796           # WARNING: Make sure you call table() again in your subclass,
797           # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
798           # and the class name is not correctly registered as a source
799           __PACKAGE__->table('baz');
800
801           sub additional_method {
802               return "I'm an additional method only needed by this app";
803           }
804
805           1;
806
807   Dynamic Sub-classing DBIx::Class proxy classes
808       AKA multi-class object inflation from one table
809
810       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 for
813       admin.  We would like to give the admin users objects
814       (DBIx::Class::Row) the same methods as a regular user but also special
815       admin only methods.  It doesn't make sense to create two separate
816       proxy-class files for this.  We would be copying all the user methods
817       into the Admin class.  There is a cleaner way to accomplish this.
818
819       Overriding the "inflate_result" method within the User proxy-class
820       gives us the effect we want.  This method is called by
821       DBIx::Class::ResultSet when inflating a result from storage.  So we
822       grab the object being returned, inspect the values we are looking for,
823       bless it if it's an admin object, and then return it.  See the example
824       below:
825
826       Schema Definition
827
828           package My::Schema;
829
830           use base qw/DBIx::Class::Schema/;
831
832           __PACKAGE__->load_namespaces;
833
834           1;
835
836       Proxy-Class definitions
837
838           package My::Schema::Result::User;
839
840           use strict;
841           use warnings;
842           use base qw/DBIx::Class::Core/;
843
844           ### Define what our admin class is, for ensure_class_loaded()
845           my $admin_class = __PACKAGE__ . '::Admin';
846
847           __PACKAGE__->table('users');
848
849           __PACKAGE__->add_columns(qw/user_id   email    password
850                                       firstname lastname active
851                                       admin/);
852
853           __PACKAGE__->set_primary_key('user_id');
854
855           sub inflate_result {
856               my $self = shift;
857               my $ret = $self->next::method(@_);
858               if( $ret->admin ) {### If this is an admin, rebless for extra functions
859                   $self->ensure_class_loaded( $admin_class );
860                   bless $ret, $admin_class;
861               }
862               return $ret;
863           }
864
865           sub hello {
866               print "I am a regular user.\n";
867               return ;
868           }
869
870           1;
871
872
873           package My::Schema::Result::User::Admin;
874
875           use strict;
876           use warnings;
877           use base qw/My::Schema::Result::User/;
878
879           # This line is important
880           __PACKAGE__->table('users');
881
882           sub hello
883           {
884               print "I am an admin.\n";
885               return;
886           }
887
888           sub do_admin_stuff
889           {
890               print "I am doing admin stuff\n";
891               return ;
892           }
893
894           1;
895
896       Test File test.pl
897
898           use warnings;
899           use strict;
900           use My::Schema;
901
902           my $user_data = { email    => 'someguy@place.com',
903                             password => 'pass1',
904                             admin    => 0 };
905
906           my $admin_data = { email    => 'someadmin@adminplace.com',
907                              password => 'pass2',
908                              admin    => 1 };
909
910           my $schema = My::Schema->connection('dbi:Pg:dbname=test');
911
912           $schema->resultset('User')->create( $user_data );
913           $schema->resultset('User')->create( $admin_data );
914
915           ### Now we search for them
916           my $user = $schema->resultset('User')->single( $user_data );
917           my $admin = $schema->resultset('User')->single( $admin_data );
918
919           print ref $user, "\n";
920           print ref $admin, "\n";
921
922           print $user->password , "\n"; # pass1
923           print $admin->password , "\n";# pass2; inherited from User
924           print $user->hello , "\n";# I am a regular user.
925           print $admin->hello, "\n";# I am an admin.
926
927           ### The statement below will NOT print
928           print "I can do admin stuff\n" if $user->can('do_admin_stuff');
929           ### The statement below will print
930           print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
931
932       Alternatively you can use DBIx::Class::DynamicSubclass that implements
933       exactly the above functionality.
934
935   Skip result object creation for faster results
936       DBIx::Class is not built for speed, it's built for convenience and ease
937       of use, but sometimes you just need to get the data, and skip the fancy
938       objects.
939
940       To do this simply use DBIx::Class::ResultClass::HashRefInflator.
941
942        my $rs = $schema->resultset('CD');
943
944        $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
945
946        my $hash_ref = $rs->find(1);
947
948       Wasn't that easy?
949
950       Beware, changing the Result class using "result_class" in
951       DBIx::Class::ResultSet will replace any existing class completely
952       including any special components loaded using load_components, eg
953       DBIx::Class::InflateColumn::DateTime.
954
955   Get raw data for blindingly fast results
956       If the HashRefInflator solution above is not fast enough for you, you
957       can use a DBIx::Class to return values exactly as they come out of the
958       database with none of the convenience methods wrapped round them.
959
960       This is used like so:
961
962         my $cursor = $rs->cursor
963         while (my @vals = $cursor->next) {
964             # use $val[0..n] here
965         }
966
967       You will need to map the array offsets to particular columns (you can
968       use the "select" in DBIx::Class::ResultSet attribute of "search" in
969       DBIx::Class::ResultSet to force ordering).
970

RESULTSET OPERATIONS

972   Getting Schema from a ResultSet
973       To get the DBIx::Class::Schema object from a ResultSet, do the
974       following:
975
976        $rs->result_source->schema
977
978   Getting Columns Of Data
979       AKA Aggregating Data
980
981       If you want to find the sum of a particular column there are several
982       ways, the obvious one is to use search:
983
984         my $rs = $schema->resultset('Items')->search(
985           {},
986           {
987              select => [ { sum => 'Cost' } ],
988              as     => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
989           }
990         );
991         my $tc = $rs->first->get_column('total_cost');
992
993       Or, you can use the DBIx::Class::ResultSetColumn, which gets returned
994       when you ask the "ResultSet" for a column using "get_column":
995
996         my $cost = $schema->resultset('Items')->get_column('Cost');
997         my $tc = $cost->sum;
998
999       With this you can also do:
1000
1001         my $minvalue = $cost->min;
1002         my $maxvalue = $cost->max;
1003
1004       Or just iterate through the values of this column only:
1005
1006         while ( my $c = $cost->next ) {
1007           print $c;
1008         }
1009
1010         foreach my $c ($cost->all) {
1011           print $c;
1012         }
1013
1014       "ResultSetColumn" only has a limited number of built-in functions. If
1015       you need one that it doesn't have, then you can use the "func" method
1016       instead:
1017
1018         my $avg = $cost->func('AVERAGE');
1019
1020       This will cause the following SQL statement to be run:
1021
1022         SELECT AVERAGE(Cost) FROM Items me
1023
1024       Which will of course only work if your database supports this function.
1025       See DBIx::Class::ResultSetColumn for more documentation.
1026
1027   Creating a result set from a set of rows
1028       Sometimes you have a (set of) result objects that you want to put into
1029       a resultset without the need to hit the DB again. You can do that by
1030       using the set_cache method:
1031
1032        my @uploadable_groups;
1033        while (my $group = $groups->next) {
1034          if ($group->can_upload($self)) {
1035            push @uploadable_groups, $group;
1036          }
1037        }
1038        my $new_rs = $self->result_source->resultset;
1039        $new_rs->set_cache(\@uploadable_groups);
1040        return $new_rs;
1041

USING RELATIONSHIPS

1043   Create a new row in a related table
1044         my $author = $book->create_related('author', { name => 'Fred'});
1045
1046   Search in a related table
1047       Only searches for books named 'Titanic' by the author in $author.
1048
1049         my $books_rs = $author->search_related('books', { name => 'Titanic' });
1050
1051   Delete data in a related table
1052       Deletes only the book named Titanic by the author in $author.
1053
1054         $author->delete_related('books', { name => 'Titanic' });
1055
1056   Ordering a relationship result set
1057       If you always want a relation to be ordered, you can specify this when
1058       you create the relationship.
1059
1060       To order "$book->pages" by descending page_number, create the relation
1061       as follows:
1062
1063         __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => { -desc => 'page_number'} } );
1064
1065   Filtering a relationship result set
1066       If you want to get a filtered result set, you can just add to $attr as
1067       follows:
1068
1069        __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
1070
1071   Many-to-many relationship bridges
1072       This is straightforward using ManyToMany:
1073
1074         package My::User;
1075         use base 'DBIx::Class::Core';
1076         __PACKAGE__->table('user');
1077         __PACKAGE__->add_columns(qw/id name/);
1078         __PACKAGE__->set_primary_key('id');
1079         __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
1080         __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
1081
1082         package My::UserAddress;
1083         use base 'DBIx::Class::Core';
1084         __PACKAGE__->table('user_address');
1085         __PACKAGE__->add_columns(qw/user address/);
1086         __PACKAGE__->set_primary_key(qw/user address/);
1087         __PACKAGE__->belongs_to('user' => 'My::User');
1088         __PACKAGE__->belongs_to('address' => 'My::Address');
1089
1090         package My::Address;
1091         use base 'DBIx::Class::Core';
1092         __PACKAGE__->table('address');
1093         __PACKAGE__->add_columns(qw/id street town area_code country/);
1094         __PACKAGE__->set_primary_key('id');
1095         __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
1096         __PACKAGE__->many_to_many('users' => 'user_address', 'user');
1097
1098         $rs = $user->addresses(); # get all addresses for a user
1099         $rs = $address->users(); # get all users for an address
1100
1101         my $address = $user->add_to_addresses(    # returns a My::Address instance,
1102                                                   # NOT a My::UserAddress instance!
1103           {
1104             country => 'United Kingdom',
1105             area_code => 'XYZ',
1106             town => 'London',
1107             street => 'Sesame',
1108           }
1109         );
1110
1111   Relationships across DB schemas
1112       Mapping relationships across DB schemas is easy as long as the schemas
1113       themselves are all accessible via the same DBI connection. In most
1114       cases, this means that they are on the same database host as each other
1115       and your connecting database user has the proper permissions to them.
1116
1117       To accomplish this one only needs to specify the DB schema name in the
1118       table declaration, like so...
1119
1120         package MyApp::Schema::Result::Artist;
1121         use base qw/DBIx::Class::Core/;
1122
1123         __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
1124
1125         __PACKAGE__->add_columns(qw/ artist_id name /);
1126         __PACKAGE__->set_primary_key('artist_id');
1127         __PACKAGE__->has_many('cds' => 'MyApp::Schema::Result::Cd');
1128
1129         1;
1130
1131       Whatever string you specify there will be used to build the "FROM"
1132       clause in SQL queries.
1133
1134       The big drawback to this is you now have DB schema names hardcoded in
1135       your class files. This becomes especially troublesome if you have
1136       multiple instances of your application to support a change lifecycle
1137       (e.g. DEV, TEST, PROD) and the DB schemas are named based on the
1138       environment (e.g. database1_dev).
1139
1140       However, one can dynamically "map" to the proper DB schema by
1141       overriding the connection method in your Schema class and building a
1142       renaming facility, like so:
1143
1144         package MyApp::Schema;
1145         use Moose;
1146
1147         extends 'DBIx::Class::Schema';
1148
1149         around connection => sub {
1150           my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
1151
1152           my $postfix = delete $attr->{schema_name_postfix};
1153
1154           $inner->(@_);
1155
1156           if ( $postfix ) {
1157               $self->append_db_name($postfix);
1158           }
1159         };
1160
1161         sub append_db_name {
1162           my ( $self, $postfix ) = @_;
1163
1164           my @sources_with_db
1165               = grep
1166                   { $_->name =~ /^\w+\./mx }
1167                   map
1168                       { $self->source($_) }
1169                       $self->sources;
1170
1171           foreach my $source (@sources_with_db) {
1172               my $name = $source->name;
1173               $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
1174
1175               $source->name($name);
1176           }
1177         }
1178
1179         1;
1180
1181       By overriding the connection method and extracting a custom option from
1182       the provided \%attr hashref one can then simply iterate over all the
1183       Schema's ResultSources, renaming them as needed.
1184
1185       To use this facility, simply add or modify the \%attr hashref that is
1186       passed to connection, as follows:
1187
1188         my $schema
1189           = MyApp::Schema->connect(
1190             $dsn,
1191             $user,
1192             $pass,
1193             {
1194               schema_name_postfix => '_dev'
1195               # ... Other options as desired ...
1196             })
1197
1198       Obviously, one could accomplish even more advanced mapping via a hash
1199       map or a callback routine.
1200

TRANSACTIONS

1202   Transactions with txn_do
1203       As of version 0.04001, there is improved transaction support in
1204       DBIx::Class::Storage and DBIx::Class::Schema.  Here is an example of
1205       the recommended way to use it:
1206
1207         my $genus = $schema->resultset('Genus')->find(12);
1208
1209         my $coderef2 = sub {
1210           $genus->extinct(1);
1211           $genus->update;
1212         };
1213
1214         my $coderef1 = sub {
1215           $genus->add_to_species({ name => 'troglodyte' });
1216           $genus->wings(2);
1217           $genus->update;
1218           $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
1219           return $genus->species;
1220         };
1221
1222         use Try::Tiny;
1223         my $rs;
1224         try {
1225           $rs = $schema->txn_do($coderef1);
1226         } catch {
1227           # Transaction failed
1228           die "the sky is falling!"           #
1229             if ($_ =~ /Rollback failed/);     # Rollback failed
1230
1231           deal_with_failed_transaction();
1232         };
1233
1234       Note: by default "txn_do" will re-run the coderef one more time if an
1235       error occurs due to client disconnection (e.g. the server is bounced).
1236       You need to make sure that your coderef can be invoked multiple times
1237       without terrible side effects.
1238
1239       Nested transactions will work as expected. That is, only the outermost
1240       transaction will actually issue a commit to the $dbh, and a rollback at
1241       any level of any transaction will cause the entire nested transaction
1242       to fail.
1243
1244   Nested transactions and auto-savepoints
1245       If savepoints are supported by your RDBMS, it is possible to achieve
1246       true nested transactions with minimal effort. To enable auto-savepoints
1247       via nested transactions, supply the "auto_savepoint = 1" connection
1248       attribute.
1249
1250       Here is an example of true nested transactions. In the example, we
1251       start a big task which will create several rows. Generation of data for
1252       each row is a fragile operation and might fail. If we fail creating
1253       something, depending on the type of failure, we want to abort the whole
1254       task, or only skip the failed row.
1255
1256         my $schema = MySchema->connect("dbi:Pg:dbname=my_db");
1257
1258         # Start a transaction. Every database change from here on will only be
1259         # committed into the database if the try block succeeds.
1260         use Try::Tiny;
1261         my $exception;
1262         try {
1263           $schema->txn_do(sub {
1264             # SQL: BEGIN WORK;
1265
1266             my $job = $schema->resultset('Job')->create({ name=> 'big job' });
1267             # SQL: INSERT INTO job ( name) VALUES ( 'big job' );
1268
1269             for (1..10) {
1270
1271               # Start a nested transaction, which in fact sets a savepoint.
1272               try {
1273                 $schema->txn_do(sub {
1274                   # SQL: SAVEPOINT savepoint_0;
1275
1276                   my $thing = $schema->resultset('Thing')->create({ job=>$job->id });
1277                   # SQL: INSERT INTO thing ( job) VALUES ( 1 );
1278
1279                   if (rand > 0.8) {
1280                     # This will generate an error, thus setting $@
1281
1282                     $thing->update({force_fail=>'foo'});
1283                     # SQL: UPDATE thing SET force_fail = 'foo'
1284                     #      WHERE ( id = 42 );
1285                   }
1286                 });
1287               } catch {
1288                 # SQL: ROLLBACK TO SAVEPOINT savepoint_0;
1289
1290                 # There was an error while creating a $thing. Depending on the error
1291                 # we want to abort the whole transaction, or only rollback the
1292                 # changes related to the creation of this $thing
1293
1294                 # Abort the whole job
1295                 if ($_ =~ /horrible_problem/) {
1296                   print "something horrible happened, aborting job!";
1297                   die $_;                # rethrow error
1298                 }
1299
1300                 # Ignore this $thing, report the error, and continue with the
1301                 # next $thing
1302                 print "Cannot create thing: $_";
1303               }
1304               # There was no error, so save all changes since the last
1305               # savepoint.
1306
1307               # SQL: RELEASE SAVEPOINT savepoint_0;
1308             }
1309           });
1310         } catch {
1311           $exception = $_;
1312         };
1313
1314         if ($exception) {
1315           # There was an error while handling the $job. Rollback all changes
1316           # since the transaction started, including the already committed
1317           # ('released') savepoints. There will be neither a new $job nor any
1318           # $thing entry in the database.
1319
1320           # SQL: ROLLBACK;
1321
1322           print "ERROR: $exception\n";
1323         }
1324         else {
1325           # There was no error while handling the $job. Commit all changes.
1326           # Only now other connections can see the newly created $job and
1327           # @things.
1328
1329           # SQL: COMMIT;
1330
1331           print "Ok\n";
1332         }
1333
1334       In this example it might be hard to see where the rollbacks, releases
1335       and commits are happening, but it works just the same as for plain
1336       txn_do: If the try-block around txn_do fails, a rollback is issued.  If
1337       the try succeeds, the transaction is committed (or the savepoint
1338       released).
1339
1340       While you can get more fine-grained control using "svp_begin",
1341       "svp_release" and "svp_rollback", it is strongly recommended to use
1342       "txn_do" with coderefs.
1343
1344   Simple Transactions with DBIx::Class::Storage::TxnScopeGuard
1345       An easy way to use transactions is with
1346       DBIx::Class::Storage::TxnScopeGuard. See "Automatically creating
1347       related objects" for an example.
1348
1349       Note that unlike txn_do, TxnScopeGuard will only make sure the
1350       connection is alive when issuing the "BEGIN" statement. It will not
1351       (and really can not) retry if the server goes away mid-operations,
1352       unlike "txn_do".
1353

SQL

1355   Creating Schemas From An Existing Database
1356       DBIx::Class::Schema::Loader will connect to a database and create a
1357       DBIx::Class::Schema and associated sources by examining the database.
1358
1359       The recommend way of achieving this is to use the dbicdump utility or
1360       the Catalyst helper, as described in Manual::Intro.
1361
1362       Alternatively, use the make_schema_at method:
1363
1364         perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
1365           -e 'make_schema_at("My::Schema", \
1366           { db_schema => 'myschema', components => ["InflateColumn::DateTime"] }, \
1367           [ "dbi:Pg:dbname=foo", "username", "password" ])'
1368
1369       This will create a tree of files rooted at "./lib/My/Schema/"
1370       containing source definitions for all the tables found in the
1371       "myschema" schema in the "foo" database.
1372
1373   Creating DDL SQL
1374       The following functionality requires you to have SQL::Translator (also
1375       known as "SQL Fairy") installed.
1376
1377       To create a set of database-specific .sql files for the above schema:
1378
1379        my $schema = My::Schema->connect($dsn);
1380        $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1381                               '0.1',
1382                               './dbscriptdir/'
1383                               );
1384
1385       By default this will create schema files in the current directory, for
1386       MySQL, SQLite and PostgreSQL, using the $VERSION from your Schema.pm.
1387
1388       To create a new database using the schema:
1389
1390        my $schema = My::Schema->connect($dsn);
1391        $schema->deploy({ add_drop_table => 1});
1392
1393       To import created .sql files using the mysql client:
1394
1395         mysql -h "host" -D "database" -u "user" -p < My_Schema_1.0_MySQL.sql
1396
1397       To create "ALTER TABLE" conversion scripts to update a database to a
1398       newer version of your schema at a later point, first set a new $VERSION
1399       in your Schema file, then:
1400
1401        my $schema = My::Schema->connect($dsn);
1402        $schema->create_ddl_dir(['MySQL', 'SQLite', 'PostgreSQL'],
1403                                '0.2',
1404                                '/dbscriptdir/',
1405                                '0.1'
1406                                );
1407
1408       This will produce new database-specific .sql files for the new version
1409       of the schema, plus scripts to convert from version 0.1 to 0.2. This
1410       requires that the files for 0.1 as created above are available in the
1411       given directory to diff against.
1412
1413   Select from dual
1414       Dummy tables are needed by some databases to allow calling functions or
1415       expressions that aren't based on table content, for examples of how
1416       this applies to various database types, see:
1417       <http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
1418
1419       Note: If you're using Oracles dual table don't ever do anything other
1420       than a select, if you CRUD on your dual table you *will* break your
1421       database.
1422
1423       Make a table class as you would for any other table
1424
1425         package MyAppDB::Dual;
1426         use strict;
1427         use warnings;
1428         use base 'DBIx::Class::Core';
1429         __PACKAGE__->table("Dual");
1430         __PACKAGE__->add_columns(
1431           "dummy",
1432           { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
1433         );
1434
1435       Once you've loaded your table class select from it using "select" and
1436       "as" instead of "columns"
1437
1438         my $rs = $schema->resultset('Dual')->search(undef,
1439           { select => [ 'sydate' ],
1440             as     => [ 'now' ]
1441           },
1442         );
1443
1444       All you have to do now is be careful how you access your resultset, the
1445       below will not work because there is no column called 'now' in the Dual
1446       table class
1447
1448         while (my $dual = $rs->next) {
1449           print $dual->now."\n";
1450         }
1451         # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
1452
1453       You could of course use 'dummy' in "as" instead of 'now', or
1454       "add_columns" to your Dual class for whatever you wanted to select from
1455       dual, but that's just silly, instead use "get_column"
1456
1457         while (my $dual = $rs->next) {
1458           print $dual->get_column('now')."\n";
1459         }
1460
1461       Or use "cursor"
1462
1463         my $cursor = $rs->cursor;
1464         while (my @vals = $cursor->next) {
1465           print $vals[0]."\n";
1466         }
1467
1468       In case you're going to use this "trick" together with "deploy" in
1469       DBIx::Class::Schema or "create_ddl_dir" in DBIx::Class::Schema a table
1470       called "dual" will be created in your current schema. This would
1471       overlap "sys.dual" and you could not fetch "sysdate" or
1472       "sequence.nextval" anymore from dual. To avoid this problem, just tell
1473       SQL::Translator to not create table dual:
1474
1475           my $sqlt_args = {
1476               add_drop_table => 1,
1477               parser_args    => { sources => [ grep $_ ne 'Dual', schema->sources ] },
1478           };
1479           $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
1480
1481       Or use DBIx::Class::ResultClass::HashRefInflator
1482
1483         $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
1484         while ( my $dual = $rs->next ) {
1485           print $dual->{now}."\n";
1486         }
1487
1488       Here are some example "select" conditions to illustrate the different
1489       syntax you could use for doing stuff like
1490       "oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')"
1491
1492         # get a sequence value
1493         select => [ 'A_SEQ.nextval' ],
1494
1495         # get create table sql
1496         select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
1497
1498         # get a random num between 0 and 100
1499         select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
1500
1501         # what year is it?
1502         select => [ { 'extract' => [ \'year from sysdate' ] } ],
1503
1504         # do some math
1505         select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
1506
1507         # which day of the week were you born on?
1508         select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
1509
1510         # select 16 rows from dual
1511         select   => [ "'hello'" ],
1512         as       => [ 'world' ],
1513         group_by => [ 'cube( 1, 2, 3, 4 )' ],
1514
1515   Adding Indexes And Functions To Your SQL
1516       Often you will want indexes on columns on your table to speed up
1517       searching. To do this, create a method called "sqlt_deploy_hook" in the
1518       relevant source class (refer to the advanced callback system if you
1519       wish to share a hook between multiple sources):
1520
1521        package My::Schema::Result::Artist;
1522
1523        __PACKAGE__->table('artist');
1524        __PACKAGE__->add_columns(id => { ... }, name => { ... })
1525
1526        sub sqlt_deploy_hook {
1527          my ($self, $sqlt_table) = @_;
1528
1529          $sqlt_table->add_index(name => 'idx_name', fields => ['name']);
1530        }
1531
1532        1;
1533
1534       Sometimes you might want to change the index depending on the type of
1535       the database for which SQL is being generated:
1536
1537         my ($db_type = $sqlt_table->schema->translator->producer_type)
1538           =~ s/^SQL::Translator::Producer:://;
1539
1540       You can also add hooks to the schema level to stop certain tables being
1541       created:
1542
1543        package My::Schema;
1544
1545        ...
1546
1547        sub sqlt_deploy_hook {
1548          my ($self, $sqlt_schema) = @_;
1549
1550          $sqlt_schema->drop_table('table_name');
1551        }
1552
1553       You could also add views, procedures or triggers to the output using
1554       "add_view" in SQL::Translator::Schema, "add_procedure" in
1555       SQL::Translator::Schema or "add_trigger" in SQL::Translator::Schema.
1556
1557   Schema versioning
1558       The following example shows simplistically how you might use
1559       DBIx::Class to deploy versioned schemas to your customers. The basic
1560       process is as follows:
1561
1562       1.  Create a DBIx::Class schema
1563
1564       2.  Save the schema
1565
1566       3.  Deploy to customers
1567
1568       4.  Modify schema to change functionality
1569
1570       5.  Deploy update to customers
1571
1572       Create a DBIx::Class schema
1573
1574       This can either be done manually, or generated from an existing
1575       database as described under "Creating Schemas From An Existing
1576       Database"
1577
1578       Save the schema
1579
1580       Call "create_ddl_dir" in DBIx::Class::Schema as above under "Creating
1581       DDL SQL".
1582
1583       Deploy to customers
1584
1585       There are several ways you could deploy your schema. These are probably
1586       beyond the scope of this recipe, but might include:
1587
1588       1.  Require customer to apply manually using their RDBMS.
1589
1590       2.  Package along with your app, making database dump/schema
1591           update/tests all part of your install.
1592
1593       Modify the schema to change functionality
1594
1595       As your application evolves, it may be necessary to modify your schema
1596       to change functionality. Once the changes are made to your schema in
1597       DBIx::Class, export the modified schema and the conversion scripts as
1598       in "Creating DDL SQL".
1599
1600       Deploy update to customers
1601
1602       Add the DBIx::Class::Schema::Versioned schema component to your Schema
1603       class. This will add a new table to your database called
1604       "dbix_class_schema_vesion" which will keep track of which version is
1605       installed and warn if the user tries to run a newer schema version than
1606       the database thinks it has.
1607
1608       Alternatively, you can send the conversion SQL scripts to your
1609       customers as above.
1610
1611   Setting quoting for the generated SQL
1612       If the database contains column names with spaces and/or reserved
1613       words, they need to be quoted in the SQL queries. This is done using:
1614
1615        $schema->storage->sql_maker->quote_char([ qw/[ ]/] );
1616        $schema->storage->sql_maker->name_sep('.');
1617
1618       The first sets the quote characters. Either a pair of matching
1619       brackets, or a """ or "'":
1620
1621        $schema->storage->sql_maker->quote_char('"');
1622
1623       Check the documentation of your database for the correct quote
1624       characters to use. "name_sep" needs to be set to allow the SQL
1625       generator to put the quotes the correct place, and defaults to "." if
1626       not supplied.
1627
1628       In most cases you should set these as part of the arguments passed to
1629       "connect" in DBIx::Class::Schema:
1630
1631        my $schema = My::Schema->connect(
1632         'dbi:mysql:my_db',
1633         'db_user',
1634         'db_password',
1635         {
1636           quote_char => '"',
1637           name_sep   => '.'
1638         }
1639        )
1640
1641       In some cases, quoting will be required for all users of a schema. To
1642       enforce this, you can also overload the "connection" method for your
1643       schema class:
1644
1645        sub connection {
1646            my $self = shift;
1647            my $rv = $self->next::method( @_ );
1648            $rv->storage->sql_maker->quote_char([ qw/[ ]/ ]);
1649            $rv->storage->sql_maker->name_sep('.');
1650            return $rv;
1651        }
1652
1653   Working with PostgreSQL array types
1654       You can also assign values to PostgreSQL array columns by passing array
1655       references in the "\%columns" ("\%vals") hashref of the "create" in
1656       DBIx::Class::ResultSet and "update" in DBIx::Class::Row family of
1657       methods:
1658
1659         $resultset->create({
1660           numbers => [1, 2, 3]
1661         });
1662
1663         $result->update(
1664           {
1665             numbers => [1, 2, 3]
1666           },
1667           {
1668             day => '2008-11-24'
1669           }
1670         );
1671
1672       In conditions (e.g. "\%cond" in the "search" in DBIx::Class::ResultSet
1673       family of methods) you cannot directly use array references (since this
1674       is interpreted as a list of values to be "OR"ed), but you can use the
1675       following syntax to force passing them as bind values:
1676
1677         $resultset->search(
1678           {
1679             numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
1680           }
1681         );
1682
1683       See "array_datatypes" in SQL::Abstract and "Literal SQL with
1684       placeholders and bind values (subqueries)" in SQL::Abstract for more
1685       explanation. Note that DBIx::Class sets "bindtype" in SQL::Abstract to
1686       "columns", so you must pass the bind values (the "[1, 2, 3]" arrayref
1687       in the above example) wrapped in arrayrefs together with the column
1688       name, like this: "[column_name => value]".
1689
1690   Formatting DateTime objects in queries
1691       To ensure "WHERE" conditions containing DateTime arguments are properly
1692       formatted to be understood by your RDBMS, you must use the DateTime
1693       formatter returned by "datetime_parser" in DBIx::Class::Storage::DBI to
1694       format any DateTime objects you pass to search conditions. Any Storage
1695       object attached to your Schema provides a correct DateTime formatter,
1696       so all you have to do is:
1697
1698         my $dtf = $schema->storage->datetime_parser;
1699         my $rs = $schema->resultset('users')->search(
1700           {
1701             signup_date => {
1702               -between => [
1703                 $dtf->format_datetime($dt_start),
1704                 $dtf->format_datetime($dt_end),
1705               ],
1706             }
1707           },
1708         );
1709
1710       Without doing this the query will contain the simple stringification of
1711       the "DateTime" object, which almost never matches the RDBMS
1712       expectations.
1713
1714       This kludge is necessary only for conditions passed to search and
1715       "find" in DBIx::Class::ResultSet, whereas create and "update" in
1716       DBIx::Class::Row (but not "update" in DBIx::Class::ResultSet) are
1717       DBIx::Class::InflateColumn-aware and will do the right thing when
1718       supplied an inflated DateTime object.
1719
1720   Using Unicode
1721       When using unicode character data there are two alternatives - either
1722       your database supports unicode characters (including setting the utf8
1723       flag on the returned string), or you need to encode/decode data
1724       appropriately each time a string field is inserted into or retrieved
1725       from the database. It is better to avoid encoding/decoding data and to
1726       use your database's own unicode capabilities if at all possible.
1727
1728       The DBIx::Class::UTF8Columns component handles storing selected unicode
1729       columns in a database that does not directly support unicode. If used
1730       with a database that does correctly handle unicode then strange and
1731       unexpected data corrupt will occur.
1732
1733       The Catalyst Wiki Unicode page at
1734       <http://wiki.catalystframework.org/wiki/tutorialsandhowtos/using_unicode>
1735       has additional information on the use of Unicode with Catalyst and
1736       DBIx::Class.
1737
1738       The following databases do correctly handle unicode data:-
1739
1740       MySQL
1741
1742       MySQL supports unicode, and will correctly flag utf8 data from the
1743       database if the "mysql_enable_utf8" is set in the connect options.
1744
1745         my $schema = My::Schema->connection('dbi:mysql:dbname=test',
1746                                             $user, $pass,
1747                                             { mysql_enable_utf8 => 1} );
1748
1749       When set, a data retrieved from a textual column type (char, varchar,
1750       etc) will have the UTF-8 flag turned on if necessary. This enables
1751       character semantics on that string. You will also need to ensure that
1752       your database / table / column is configured to use UTF8. See Chapter
1753       10 of the mysql manual for details.
1754
1755       See DBD::mysql for further details.
1756
1757       Oracle
1758
1759       Information about Oracle support for unicode can be found in "UNICODE"
1760       in DBD::Oracle.
1761
1762       PostgreSQL
1763
1764       PostgreSQL supports unicode if the character set is correctly set at
1765       database creation time. Additionally the "pg_enable_utf8" should be set
1766       to ensure unicode data is correctly marked.
1767
1768         my $schema = My::Schema->connection('dbi:Pg:dbname=test',
1769                                             $user, $pass,
1770                                             { pg_enable_utf8 => 1} );
1771
1772       Further information can be found in DBD::Pg.
1773
1774       SQLite
1775
1776       SQLite version 3 and above natively use unicode internally. To
1777       correctly mark unicode strings taken from the database, the
1778       "sqlite_unicode" flag should be set at connect time (in versions of
1779       DBD::SQLite prior to 1.27 this attribute was named "unicode").
1780
1781         my $schema = My::Schema->connection('dbi:SQLite:/tmp/test.db',
1782                                             '', '',
1783                                             { sqlite_unicode => 1} );
1784

BOOTSTRAPPING/MIGRATING

1786   Easy migration from class-based to schema-based setup
1787       You want to start using the schema-based approach to DBIx::Class (see
1788       "Setting it up manually" in DBIx::Class::Manual::Intro), but have an
1789       established class-based setup with lots of existing classes that you
1790       don't want to move by hand. Try this nifty script instead:
1791
1792         use MyDB;
1793         use SQL::Translator;
1794
1795         my $schema = MyDB->schema_instance;
1796
1797         my $translator           =  SQL::Translator->new(
1798             debug                => $debug          ||  0,
1799             trace                => $trace          ||  0,
1800             no_comments          => $no_comments    ||  0,
1801             show_warnings        => $show_warnings  ||  0,
1802             add_drop_table       => $add_drop_table ||  0,
1803             validate             => $validate       ||  0,
1804             parser_args          => {
1805                'DBIx::Schema'    => $schema,
1806                                     },
1807             producer_args   => {
1808                 'prefix'         => 'My::Schema',
1809                                },
1810         );
1811
1812         $translator->parser('SQL::Translator::Parser::DBIx::Class');
1813         $translator->producer('SQL::Translator::Producer::DBIx::Class::File');
1814
1815         my $output = $translator->translate(@args) or die
1816                 "Error: " . $translator->error;
1817
1818         print $output;
1819
1820       You could use Module::Find to search for all subclasses in the MyDB::*
1821       namespace, which is currently left as an exercise for the reader.
1822

OVERLOADING METHODS

1824       DBIx::Class uses the Class::C3 package, which provides for redispatch
1825       of method calls, useful for things like default values and triggers.
1826       You have to use calls to "next::method" to overload methods. More
1827       information on using Class::C3 with DBIx::Class can be found in
1828       DBIx::Class::Manual::Component.
1829
1830   Setting default values for a row
1831       It's as simple as overriding the "new" method.  Note the use of
1832       "next::method".
1833
1834         sub new {
1835           my ( $class, $attrs ) = @_;
1836
1837           $attrs->{foo} = 'bar' unless defined $attrs->{foo};
1838
1839           my $new = $class->next::method($attrs);
1840
1841           return $new;
1842         }
1843
1844       For more information about "next::method", look in the Class::C3
1845       documentation. See also DBIx::Class::Manual::Component for more ways to
1846       write your own base classes to do this.
1847
1848       People looking for ways to do "triggers" with DBIx::Class are probably
1849       just looking for this.
1850
1851   Changing one field whenever another changes
1852       For example, say that you have three columns, "id", "number", and
1853       "squared".  You would like to make changes to "number" and have
1854       "squared" be automagically set to the value of "number" squared.  You
1855       can accomplish this by wrapping the "number" accessor with the "around"
1856       method modifier, available through either Class::Method::Modifiers,
1857       Moose or Moose-like modules):
1858
1859         around number => sub {
1860           my ($orig, $self) = (shift, shift);
1861
1862           if (@_) {
1863             my $value = $_[0];
1864             $self->squared( $value * $value );
1865           }
1866
1867           $self->$orig(@_);
1868         };
1869
1870       Note that the hard work is done by the call to "$self->$orig", which
1871       redispatches your call to store_column in the superclass(es).
1872
1873       Generally, if this is a calculation your database can easily do, try
1874       and avoid storing the calculated value, it is safer to calculate when
1875       needed, than rely on the data being in sync.
1876
1877   Automatically creating related objects
1878       You might have a class "Artist" which has many "CD"s.  Further, you
1879       want to create a "CD" object every time you insert an "Artist" object.
1880       You can accomplish this by overriding "insert" on your objects:
1881
1882         sub insert {
1883           my ( $self, @args ) = @_;
1884           $self->next::method(@args);
1885           $self->create_related ('cds', \%initial_cd_data );
1886           return $self;
1887         }
1888
1889       If you want to wrap the two inserts in a transaction (for consistency,
1890       an excellent idea), you can use the awesome
1891       DBIx::Class::Storage::TxnScopeGuard:
1892
1893         sub insert {
1894           my ( $self, @args ) = @_;
1895
1896           my $guard = $self->result_source->schema->txn_scope_guard;
1897
1898           $self->next::method(@args);
1899           $self->create_related ('cds', \%initial_cd_data );
1900
1901           $guard->commit;
1902
1903           return $self
1904         }
1905
1906   Wrapping/overloading a column accessor
1907       Problem:
1908
1909       Say you have a table "Camera" and want to associate a description with
1910       each camera. For most cameras, you'll be able to generate the
1911       description from the other columns. However, in a few special cases you
1912       may want to associate a custom description with a camera.
1913
1914       Solution:
1915
1916       In your database schema, define a description field in the "Camera"
1917       table that can contain text and null values.
1918
1919       In DBIC, we'll overload the column accessor to provide a sane default
1920       if no custom description is defined. The accessor will either return or
1921       generate the description, depending on whether the field is null or
1922       not.
1923
1924       First, in your "Camera" schema class, define the description field as
1925       follows:
1926
1927         __PACKAGE__->add_columns(description => { accessor => '_description' });
1928
1929       Next, we'll define the accessor-wrapper subroutine:
1930
1931         sub description {
1932             my $self = shift;
1933
1934             # If there is an update to the column, we'll let the original accessor
1935             # deal with it.
1936             return $self->_description(@_) if @_;
1937
1938             # Fetch the column value.
1939             my $description = $self->_description;
1940
1941             # If there's something in the description field, then just return that.
1942             return $description if defined $description && length $descripton;
1943
1944             # Otherwise, generate a description.
1945             return $self->generate_description;
1946         }
1947

DEBUGGING AND PROFILING

1949   DBIx::Class objects with Data::Dumper
1950       Data::Dumper can be a very useful tool for debugging, but sometimes it
1951       can be hard to find the pertinent data in all the data it can generate.
1952       Specifically, if one naively tries to use it like so,
1953
1954         use Data::Dumper;
1955
1956         my $cd = $schema->resultset('CD')->find(1);
1957         print Dumper($cd);
1958
1959       several pages worth of data from the CD object's schema and result
1960       source will be dumped to the screen. Since usually one is only
1961       interested in a few column values of the object, this is not very
1962       helpful.
1963
1964       Luckily, it is possible to modify the data before Data::Dumper outputs
1965       it. Simply define a hook that Data::Dumper will call on the object
1966       before dumping it. For example,
1967
1968         package My::DB::CD;
1969
1970         sub _dumper_hook {
1971           $_[0] = bless {
1972             %{ $_[0] },
1973             result_source => undef,
1974           }, ref($_[0]);
1975         }
1976
1977         [...]
1978
1979         use Data::Dumper;
1980
1981         local $Data::Dumper::Freezer = '_dumper_hook';
1982
1983         my $cd = $schema->resultset('CD')->find(1);
1984         print Dumper($cd);
1985                # dumps $cd without its ResultSource
1986
1987       If the structure of your schema is such that there is a common base
1988       class for all your table classes, simply put a method similar to
1989       "_dumper_hook" in the base class and set $Data::Dumper::Freezer to its
1990       name and Data::Dumper will automagically clean up your data before
1991       printing it. See "EXAMPLES" in Data::Dumper for more information.
1992
1993   Profiling
1994       When you enable DBIx::Class::Storage's debugging it prints the SQL
1995       executed as well as notifications of query completion and transaction
1996       begin/commit.  If you'd like to profile the SQL you can subclass the
1997       DBIx::Class::Storage::Statistics class and write your own profiling
1998       mechanism:
1999
2000         package My::Profiler;
2001         use strict;
2002
2003         use base 'DBIx::Class::Storage::Statistics';
2004
2005         use Time::HiRes qw(time);
2006
2007         my $start;
2008
2009         sub query_start {
2010           my $self = shift();
2011           my $sql = shift();
2012           my @params = @_;
2013
2014           $self->print("Executing $sql: ".join(', ', @params)."\n");
2015           $start = time();
2016         }
2017
2018         sub query_end {
2019           my $self = shift();
2020           my $sql = shift();
2021           my @params = @_;
2022
2023           my $elapsed = sprintf("%0.4f", time() - $start);
2024           $self->print("Execution took $elapsed seconds.\n");
2025           $start = undef;
2026         }
2027
2028         1;
2029
2030       You can then install that class as the debugging object:
2031
2032         __PACKAGE__->storage->debugobj(new My::Profiler());
2033         __PACKAGE__->storage->debug(1);
2034
2035       A more complicated example might involve storing each execution of SQL
2036       in an array:
2037
2038         sub query_end {
2039           my $self = shift();
2040           my $sql = shift();
2041           my @params = @_;
2042
2043           my $elapsed = time() - $start;
2044           push(@{ $calls{$sql} }, {
2045               params => \@params,
2046               elapsed => $elapsed
2047           });
2048         }
2049
2050       You could then create average, high and low execution times for an SQL
2051       statement and dig down to see if certain parameters cause aberrant
2052       behavior.  You might want to check out DBIx::Class::QueryLog as well.
2053

IMPROVING PERFORMANCE

2055       ·   Install Class::XSAccessor to speed up Class::Accessor::Grouped.
2056
2057       ·   On Perl 5.8 install Class::C3::XS.
2058
2059       ·   prefetch relationships, where possible. See "Using joins and
2060           prefetch".
2061
2062       ·   Use populate in void context to insert data when you don't need the
2063           resulting result objects, if possible, but see the caveats.
2064
2065           When inserting many rows, for best results, populate a large number
2066           of rows at a time, but not so large that the table is locked for an
2067           unacceptably long time.
2068
2069           If using create instead, use a transaction and commit every "X"
2070           rows; where "X" gives you the best performance without locking the
2071           table for too long.
2072
2073       ·   When selecting many rows, if you don't need full-blown
2074           DBIx::Class::Row objects, consider using
2075           DBIx::Class::ResultClass::HashRefInflator.
2076
2077       ·   See also "STARTUP SPEED" and "MEMORY USAGE" in this document.
2078

STARTUP SPEED

2080       DBIx::Class programs can have a significant startup delay as the ORM
2081       loads all the relevant classes. This section examines techniques for
2082       reducing the startup delay.
2083
2084       These tips are listed in order of decreasing effectiveness - so the
2085       first tip, if applicable, should have the greatest effect on your
2086       application.
2087
2088   Statically Define Your Schema
2089       If you are using DBIx::Class::Schema::Loader to build the classes
2090       dynamically based on the database schema then there will be a
2091       significant startup delay.
2092
2093       For production use a statically defined schema (which can be generated
2094       using DBIx::Class::Schema::Loader to dump the database schema once -
2095       see make_schema_at and dump_directory for more details on creating
2096       static schemas from a database).
2097
2098   Move Common Startup into a Base Class
2099       Typically DBIx::Class result classes start off with
2100
2101           use base qw/DBIx::Class::Core/;
2102           __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2103
2104       If this preamble is moved into a common base class:-
2105
2106           package MyDBICbase;
2107
2108           use base qw/DBIx::Class::Core/;
2109           __PACKAGE__->load_components(qw/InflateColumn::DateTime/);
2110           1;
2111
2112       and each result class then uses this as a base:-
2113
2114           use base qw/MyDBICbase/;
2115
2116       then the load_components is only performed once, which can result in a
2117       considerable startup speedup for schemas with many classes.
2118
2119   Explicitly List Schema Result Classes
2120       The schema class will normally contain
2121
2122           __PACKAGE__->load_classes();
2123
2124       to load the result classes. This will use Module::Find to find and load
2125       the appropriate modules. Explicitly defining the classes you wish to
2126       load will remove the overhead of Module::Find and the related directory
2127       operations:
2128
2129           __PACKAGE__->load_classes(qw/ CD Artist Track /);
2130
2131       If you are instead using the load_namespaces syntax to load the
2132       appropriate classes there is not a direct alternative avoiding
2133       Module::Find.
2134

MEMORY USAGE

2136   Cached statements
2137       DBIx::Class normally caches all statements with prepare_cached(). This
2138       is normally a good idea, but if too many statements are cached, the
2139       database may use too much memory and may eventually run out and fail
2140       entirely. If you suspect this may be the case, you may want to examine
2141       DBI's CachedKids hash:
2142
2143           # print all currently cached prepared statements
2144           print for keys %{$schema->storage->dbh->{CachedKids}};
2145           # get a count of currently cached prepared statements
2146           my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
2147
2148       If it's appropriate, you can simply clear these statements,
2149       automatically deallocating them in the database:
2150
2151           my $kids = $schema->storage->dbh->{CachedKids};
2152           delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
2153
2154       But what you probably want is to expire unused statements and not those
2155       that are used frequently.  You can accomplish this with Tie::Cache or
2156       Tie::Cache::LRU:
2157
2158           use Tie::Cache;
2159           use DB::Main;
2160           my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
2161               on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },
2162           });
2163

FURTHER QUESTIONS?

2165       Check the list of additional DBIC resources.
2166
2168       This module is free software copyright by the DBIx::Class (DBIC)
2169       authors. You can redistribute it and/or modify it under the same terms
2170       as the DBIx::Class library.
2171
2172
2173
2174perl v5.30.1                      2020-01-29  DBIx::Class::Manual::Cookbook(3)
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