3 DBIx::Class::Manual::FAQ - Frequently Asked Questions (in theory)
7 This document is intended as an anti-map of the documentation. If you
8 know what you want to do, but not how to do it in L<DBIx::Class>, then
9 look here. It does B<not> contain much code or examples, it just gives
10 explanations and pointers to the correct pieces of documentation to
17 =head2 Getting started
21 =item .. create a database to use?
23 First, choose a database. For testing/experimenting, we recommend
24 L<DBD::SQLite>, which is a self-contained small database (i.e. all you
25 need to do is to install L<DBD::SQLite> from CPAN, and it works).
27 Next, spend some time defining which data you need to store, and how
28 it relates to the other data you have. For some help on normalisation,
29 go to L<http://b62.tripod.com/doc/dbbase.htm>.
31 Now, decide whether you want to have the database itself be the
32 definitive source of information about the data layout, or your
33 DBIx::Class schema. If it's the former, look up the documentation for
34 your database, eg. L<http://sqlite.org/lang_createtable.html>, on how
35 to create tables, and start creating them. For a nice universal
36 interface to your database, you can try L<DBI::Shell>. If you decided
37 on the latter choice, read the FAQ on setting up your classes
38 manually, and the one on creating tables from your schema.
40 =item .. use DBIx::Class with L<Catalyst>?
42 Install L<Catalyst::Model::DBIC::Schema> from CPAN. See its
43 documentation, or below, for further details.
45 =item .. set up my DBIx::Class classes automatically from my database?
47 Install L<DBIx::Class::Schema::Loader> from CPAN, and read its documentation.
49 =item .. set up my DBIx::Class classes manually?
51 Look at the L<DBIx::Class::Manual::Example> and come back here if you get lost.
53 =item .. create my database tables from my DBIx::Class schema?
55 Create your classes manually, as above. Write a script that calls
56 L<DBIx::Class::Schema/deploy>. See there for details, or the
57 L<DBIx::Class::Manual::Cookbook>.
59 =item .. store/retrieve Unicode data in my database?
61 Make sure you database supports Unicode and set the connect
62 attributes appropriately - see
63 L<DBIx::Class::Manual::Cookbook/Using Unicode>
65 =item .. connect to my database?
67 Once you have created all the appropriate table/source classes, and an
68 overall L<Schema|DBIx::Class::Schema> class, you can start using
69 them in an application. To do this, you need to create a central
70 Schema object, which is used to access all the data in the various
71 tables. See L<DBIx::Class::Schema/connect> for details. The actual
72 connection does not happen until you actually request data, so don't
73 be alarmed if the error from incorrect connection details happens a
76 =item .. use DBIx::Class across multiple databases?
78 If your database server allows you to run queries across multiple
79 databases at once, then so can DBIx::Class. All you need to do is make
80 sure you write the database name as part of the
81 L<table|DBIx::Class::ResultSourceProxy::Table/table> call. Eg:
83 __PACKAGE__->table('mydb.mytablename');
85 And load all the Result classes for both / all databases by calling
86 L<DBIx::Class::Schema/load_namespaces>.
88 =item .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
90 Add the name of the schema to the table name, when invoking
91 L<table|DBIx::Class::ResultSourceProxy::Table/table>, and make sure the user
92 you are about to connect as has permissions to read/write all the
93 schemas/tables as necessary.
101 =item .. tell DBIx::Class about relationships between my tables?
103 There are a variety of relationship types that come pre-defined for
104 you to use. These are all listed in L<DBIx::Class::Relationship>. If
105 you need a non-standard type, or more information, look in
106 L<DBIx::Class::Relationship::Base>.
108 =item .. define a one-to-many relationship?
110 This is called a C<has_many> relationship on the one side, and a
111 C<belongs_to> relationship on the many side. Currently these need to
112 be set up individually on each side. See L<DBIx::Class::Relationship>
115 =item .. define a relationship where this table contains another table's primary key? (foreign key)
117 Create a C<belongs_to> relationship for the field containing the
118 foreign key. See L<DBIx::Class::Relationship/belongs_to>.
120 =item .. define a foreign key relationship where the key field may contain NULL?
122 Just create a C<belongs_to> relationship, as above. If the column is
123 NULL then the inflation to the foreign object will not happen. This
124 has a side effect of not always fetching all the relevant data, if you
125 use a nullable foreign-key relationship in a JOIN, then you probably
126 want to set the C<join_type> to C<left>.
128 =item .. define a relationship where the key consists of more than one column?
130 Instead of supplying a single column name, all relationship types also
131 allow you to supply a hashref containing the condition across which
132 the tables are to be joined. The condition may contain as many fields
133 as you like. See L<DBIx::Class::Relationship::Base>.
135 =item .. define a relationship bridge across an intermediate table? (many-to-many)
137 The term 'relationship' is used loosely with many_to_many as it is not considered a
138 relationship in the fullest sense. For more info, read the documentation on L<DBIx::Class::Relationship/many_to_many>.
140 =item .. stop DBIx::Class from attempting to cascade deletes on my has_many and might_have relationships?
142 By default, DBIx::Class cascades deletes and updates across
143 C<has_many> and C<might_have> relationships. You can disable this
144 behaviour on a per-relationship basis by supplying
145 C<< cascade_delete => 0 >> in the relationship attributes.
147 The cascaded operations are performed after the requested delete or
148 update, so if your database has a constraint on the relationship, it
149 will have deleted/updated the related records or raised an exception
150 before DBIx::Class gets to perform the cascaded operation.
152 See L<DBIx::Class::Relationship>.
154 =item .. use a relationship?
156 Use its name. An accessor is created using the name. See examples in
157 L<DBIx::Class::Manual::Cookbook/USING RELATIONSHIPS>.
165 =item .. search for data?
167 Create a C<$schema> object, as mentioned above in L</.. connect to my
169 L<ResultSet|DBIx::Class::Manual::Glossary/ResultSet> that you want to
170 search in, by calling C<< $schema->resultset('MySource') >> and call
171 C<search> on it. See L<DBIx::Class::ResultSet/search>.
173 =item .. search using database functions?
175 Supplying something like:
177 ->search({'mydatefield' => 'now()'})
179 to search, will probably not do what you expect. It will quote the
180 text "now()", instead of trying to call the function. To provide
181 literal, unquoted text you need to pass in a scalar reference, like
184 ->search({'mydatefield' => \'now()'})
186 =item .. sort the results of my search?
188 Supply a list of columns you want to sort by to the C<order_by>
189 attribute. See L<DBIx::Class::ResultSet/order_by>.
191 =item .. sort my results based on fields I've aliased using C<as>?
193 You didn't alias anything, since L<as|DBIx::Class::ResultSet/as>
194 B<has nothing to do> with the produced SQL. See
195 L<DBIx::Class::ResultSet/select> for details.
197 =item .. group the results of my search?
199 Supply a list of columns you want to group on, to the C<group_by>
200 attribute, see L<DBIx::Class::ResultSet/group_by>.
202 =item .. group my results based on fields I've aliased using C<as>?
204 You don't. See the explanation on ordering by an alias above.
206 =item .. filter the results of my search?
208 The first argument to C<search> is a hashref of accessor names and
209 values to filter them by, for example:
211 ->search({'created_time' => { '>=', '2006-06-01 00:00:00' } })
213 Note that to use a function here you need to make it a scalar
216 ->search({'created_time' => { '>=', \'yesterday()' } })
218 =item .. search in several tables simultaneously?
220 To search in two related tables, you first need to set up appropriate
221 relationships between their respective classes. When searching you
222 then supply the name of the relationship to the C<join> attribute in
223 your search, for example when searching in the Books table for all the
224 books by the author "Fred Bloggs":
226 ->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors' })
228 The type of join created in your SQL depends on the type of
229 relationship between the two tables, see L<DBIx::Class::Relationship>
230 for the join used by each relationship.
232 =item .. create joins with conditions other than column equality?
234 Currently, L<DBIx::Class> can only create join conditions using
235 equality, so you're probably better off creating a C<view> in your
236 database, and using that as your source. A C<view> is a stored SQL
237 query, which can be accessed similarly to a table, see your database
238 documentation for details.
240 =item .. search with an SQL function on the left hand side?
242 To use an SQL function on the left hand side of a comparison you currently need
243 to resort to literal SQL:
245 ->search( \[ 'YEAR(date_of_birth) = ?', 1979 ] );
247 =item .. find more help on constructing searches?
249 Behind the scenes, DBIx::Class uses L<SQL::Abstract> to help construct
250 its SQL searches. So if you fail to find help in the
251 L<DBIx::Class::Manual::Cookbook>, try looking in the SQL::Abstract
254 =item .. make searches in Oracle (10gR2 and newer) case-insensitive?
256 To make Oracle behave like most RDBMS use on_connect_do to issue
257 alter session statements on database connection establishment:
259 ->on_connect_do("ALTER SESSION SET NLS_COMP = 'LINGUISTIC'");
260 ->on_connect_do("ALTER SESSION SET NLS_SORT = '<NLS>_CI'");
262 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'BINARY_CI'");
263 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'GERMAN_CI'");
265 =item .. format a DateTime object for searching?
267 L<search|DBIx::Class::ResultSet/search> and L<find|DBIx::Class::ResultSet/find>
268 do not take L<DBIx::Class::InflateColumn> into account, and so your L<DateTime>
269 object will not be correctly deflated into a format your RDBMS expects.
271 The L<datetime_parser|DBIx::Class::Storage::DBI/datetime_parser> method on your
272 storage object can be used to return the object that would normally do this, so
273 it's easy to do it manually:
275 my $dtf = $schema->storage->datetime_parser;
276 my $rs = $schema->resultset('users')->search(
280 $dtf->format_datetime($dt_start),
281 $dtf->format_datetime($dt_end),
287 With in a Result Class method, you can get this from the
288 L<C<result_source>|DBIx::Class::Row/result_source>.
290 my $dtf = $self->result_source->storage->datetime_parser;
292 This kludge is necessary only for conditions passed to
293 L<search|DBIx::Class::ResultSet/search> and L<DBIx::Class::ResultSet/find>,
294 whereas L<create|DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update>
295 (but not L<DBIx::Class::ResultSet/update>) are
296 L<DBIx::Class::InflateColumn>-aware and will do the right thing when supplied
297 an inflated L<DateTime> object.
305 =item .. fetch as much data as possible in as few select calls as possible?
307 See the prefetch examples in the L<Cookbook|DBIx::Class::Manual::Cookbook>.
309 =item .. fetch a whole column of data instead of a row?
311 Call C<get_column> on a L<DBIx::Class::ResultSet>. This returns a
312 L<DBIx::Class::ResultSetColumn>. See its documentation and the
313 L<Cookbook|DBIx::Class::Manual::Cookbook> for details.
315 =item .. fetch a formatted column?
317 In your table schema class, create a "private" column accessor with:
319 __PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });
321 Then, in the same class, implement a subroutine called "my_column" that
322 fetches the real value and does the formatting you want.
324 See the L<Cookbook|DBIx::Class::Manual::Cookbook> for more details.
326 =item .. fetch a single (or topmost) row?
328 Use the L<DBIx::Class::ResultSet/rows> and
329 L<DBIx::Class::ResultSet/order_by> attributes to order your data and
330 pick off a single row.
332 See also L<DBIx::Class::Manual::Cookbook/Retrieve one and only one row from a resultset>.
334 A less readable way is to ask a regular search to return 1 row, using
335 L<DBIx::Class::ResultSet/slice>:
337 ->search->(undef, { order_by => "id DESC" })->slice(0)
339 which (if supported by the database) will use LIMIT/OFFSET to hint to the
340 database that we really only need one row. This can result in a significant
341 speed improvement. The method using L<DBIx::Class::ResultSet/single> mentioned
342 in the cookbook can do the same if you pass a C<rows> attribute to the search.
344 =item .. refresh a row from storage?
346 Use L<DBIx::Class::Row/discard_changes>.
348 $result->discard_changes
350 Discarding changes and refreshing from storage are two sides of the same coin. When you
351 want to discard your local changes, just re-fetch the row from storage. When you want
352 to get a new, fresh copy of the row, just re-fetch the row from storage.
353 L<DBIx::Class::Row/discard_changes> does just that by re-fetching the row from storage
354 using the row's primary key.
356 =item .. fetch my data a "page" at a time?
358 Pass the C<rows> and C<page> attributes to your search, eg:
360 ->search({}, { rows => 10, page => 1});
362 =item .. get a count of all rows even when paging?
364 Call C<pager> on the paged resultset, it will return a L<Data::Page>
365 object. Calling C<total_entries> on the pager will return the correct
368 C<count> on the resultset will only return the total number in the page.
372 =head2 Inserting and updating data
376 =item .. insert a row with an auto incrementing primary key?
378 This happens automatically. After
379 L<creating|DBIx::Class::ResultSet/create> a result object, the primary
380 key value created by your database can be fetched by calling C<id> (or
381 the access of your primary key column) on the object.
383 =item .. insert a row with a primary key that uses a sequence?
385 You need to create a trigger in your database that updates your
386 primary key field from the sequence. To help PK::Auto find the next
387 key value, you can tell it the name of the sequence in the
388 C<column_info> supplied with C<add_columns>.
390 ->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });
392 =item .. insert many rows of data efficiently?
394 The C<populate> method in L<DBIx::Class::ResultSet> provides
395 efficient bulk inserts.
397 L<DBIx::Class::Fixtures> provides an alternative way to do this.
399 =item .. update a collection of rows at the same time?
401 Create a resultset using a C<search>, to filter the rows of data you
402 would like to update, then call C<update> on the resultset to change all
405 =item .. use database functions when updating rows?
407 =item .. update a column using data from another column?
409 To stop the column name from being quoted, you'll need to tell DBIC
410 that the right hand side is an SQL identifier (it will be quoted
411 properly if you have quoting enabled):
413 ->update({ somecolumn => { -ident => 'othercolumn' } })
415 This method will not retrieve the new value and put it in your Row
416 object. To fetch the new value, use the C<discard_changes> method on
419 # will return the scalar reference:
420 $result->somecolumn()
422 # issue a select using the PK to re-fetch the row data:
423 $result->discard_changes();
425 # Now returns the correct new value:
426 $result->somecolumn()
428 To update and refresh at once, chain your calls:
430 $result->update({ 'somecolumn' => { -ident => 'othercolumn' } })->discard_changes;
432 =item .. store JSON/YAML in a column and have it deflate/inflate automatically?
434 You can use L<DBIx::Class::InflateColumn> to accomplish YAML/JSON storage transparently.
436 If you want to use JSON, then in your table schema class, do the following:
440 __PACKAGE__->add_columns(qw/ ... my_column ../)
441 __PACKAGE__->inflate_column('my_column', {
442 inflate => sub { jsonToObj(shift) },
443 deflate => sub { objToJson(shift) },
446 For YAML, in your table schema class, do the following:
450 __PACKAGE__->add_columns(qw/ ... my_column ../)
451 __PACKAGE__->inflate_column('my_column', {
452 inflate => sub { YAML::Load(shift) },
453 deflate => sub { YAML::Dump(shift) },
456 This technique is an easy way to store supplemental unstructured data in a table. Be
457 careful not to overuse this capability, however. If you find yourself depending more
458 and more on some data within the inflated column, then it may be time to factor that
463 =head2 Custom methods in Result classes
465 You can add custom methods that do arbitrary things, even to unrelated tables.
466 For example, to provide a C<< $book->foo() >> method which searches the
467 cd table, you'd could add this to Book.pm:
470 my ($self, $col_data) = @_;
471 return $self->result_source->schema->resultset('cd')->search($col_data);
474 And invoke that on any Book Result object like so:
476 my $rs = $book->foo({ title => 'Down to Earth' });
478 When two tables ARE related, L<DBIx::Class::Relationship::Base> provides many
479 methods to find or create data in related tables for you. But if you want to
480 write your own methods, you can.
482 For example, to provide a C<< $book->foo() >> method to manually implement
483 what create_related() from L<DBIx::Class::Relationship::Base> does, you could
487 my ($self, $rel_name, $col_data) = @_;
488 return $self->related_resultset($rel_name)->create($col_data);
493 my $author = $book->foo('author', { name => 'Fred' });
499 =item How do I store my own (non-db) data in my DBIx::Class objects?
501 You can add your own data accessors to your Result classes.
503 One method is to use the built in mk_group_accessors (via L<Class::Accessor::Grouped>)
505 package App::Schema::Result::MyTable;
507 use parent 'DBIx::Class::Core';
509 __PACKAGE__->table('foo'); #etc
510 __PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
512 An another method is to use L<Moose> with your L<DBIx::Class> package.
514 package App::Schema::Result::MyTable;
516 use Moose; # import Moose
517 use Moose::Util::TypeConstraint; # import Moose accessor type constraints
519 extends 'DBIx::Class::Core'; # Moose changes the way we define our parent (base) package
521 has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute
523 __PACKAGE__->table('foo'); # etc
525 With either of these methods the resulting use of the accessor would be
529 # assume that somewhere in here $result will get assigned to a MyTable row
531 $result->non_column_data('some string'); # would set the non_column_data accessor
533 # some other stuff happens here
535 $result->update(); # would not inline the non_column_data accessor into the update
538 =item How do I use DBIx::Class objects in my TT templates?
540 Like normal objects, mostly. However you need to watch out for TT
541 calling methods in list context. When calling relationship accessors
542 you will not get resultsets, but a list of all the related objects.
544 Use the L<DBIx::Class::ResultSet/search_rs> method, or the
545 relationship accessor methods ending with "_rs" to work around this
548 See also L<DBIx::Class::Relationship/has_many>.
550 =item See the SQL statements my code is producing?
552 Set the shell environment variable C<DBIC_TRACE> to a true value.
554 For more info see L<DBIx::Class::Storage> for details of how
555 to turn on debugging in the environment, pass your own filehandle to
556 save debug to, or create your own callback.
558 =item Why didn't my search run any SQL?
560 L<DBIx::Class> runs the actual SQL statement as late as possible, thus
561 if you create a resultset using C<search> in scalar context, no query
562 is executed. You can create further resultset refinements by calling
563 search again or relationship accessors. The SQL query is only run when
564 you ask the resultset for an actual result object.
566 =item How do I deal with tables that lack a primary key?
568 If your table lacks a primary key, DBIx::Class can't work out which row
569 it should operate on, for example to delete or update. However, a
570 UNIQUE constraint on one or more columns allows DBIx::Class to uniquely
571 identify the row, so you can tell L<DBIx::Class::ResultSource> these
572 columns act as a primary key, even if they don't from the database's
575 $resultset->set_primary_key(@column);
577 =item How do I make my program start faster?
579 Look at the tips in L<DBIx::Class::Manual::Cookbook/"STARTUP SPEED">
581 =item How do I reduce the overhead of database queries?
583 You can reduce the overhead of object creation within L<DBIx::Class>
584 using the tips in L<DBIx::Class::Manual::Cookbook/"Skip result object creation for faster results">
585 and L<DBIx::Class::Manual::Cookbook/"Get raw data for blindingly fast results">
587 =item How do I override a run time method (e.g. a relationship accessor)?
589 If you need access to the original accessor, then you must "wrap around" the original method.
590 You can do that either with L<Moose::Manual::MethodModifiers> or L<Class::Method::Modifiers>.
591 The code example works for both modules:
593 package Your::Schema::Group;
594 use Class::Method::Modifiers;
596 # ... declare columns ...
598 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
599 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
601 # if the server group is a "super group", then return all servers
602 # otherwise return only servers that belongs to the given group
603 around 'servers' => sub {
607 return $self->$orig(@_) unless $self->is_super_group;
608 return $self->result_source->schema->resultset('Server')->all;
611 If you just want to override the original method, and don't care about the data
612 from the original accessor, then you have two options. Either use
613 L<Method::Signatures::Simple> that does most of the work for you, or do
616 L<Method::Signatures::Simple> way:
618 package Your::Schema::Group;
619 use Method::Signatures::Simple;
621 # ... declare columns ...
623 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
624 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
626 # The method keyword automatically injects the annoying my $self = shift; for you.
628 return $self->result_source->schema->resultset('Server')->search({ ... });
633 package Your::Schema::Group;
636 # ... declare columns ...
638 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
639 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
641 *servers = subname servers => sub {
643 return $self->result_source->schema->resultset('Server')->search({ ... });
648 =head2 Notes for CDBI users
652 =item Is there a way to make an object auto-stringify itself as a
653 particular column or group of columns (a-la cdbi Stringfy column
654 group, or stringify_self method) ?
656 See L<DBIx::Class::Manual::Cookbook/Stringification>
660 =head2 Troubleshooting
664 =item Help, I can't connect to postgresql!
666 If you get an error such as:
668 DBI connect('dbname=dbic','user',...) failed: could not connect to server:
669 No such file or directory Is the server running locally and accepting
670 connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
672 Likely you have/had two copies of postgresql installed simultaneously, the
673 second one will use a default port of 5433, while L<DBD::Pg> is compiled with a
674 default port of 5432.
676 You can change the port setting in C<postgresql.conf>.
678 =item I've lost or forgotten my mysql password
680 Stop mysqld and restart it with the --skip-grant-tables option.
682 Issue the following statements in the mysql client.
684 UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
691 L<http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html>.
695 =head1 FURTHER QUESTIONS?
697 Check the list of L<additional DBIC resources|DBIx::Class/GETTING HELP/SUPPORT>.
699 =head1 COPYRIGHT AND LICENSE
701 This module is free software L<copyright|DBIx::Class/COPYRIGHT AND LICENSE>
702 by the L<DBIx::Class (DBIC) authors|DBIx::Class/AUTHORS>. You can
703 redistribute it and/or modify it under the same terms as the
704 L<DBIx::Class library|DBIx::Class/COPYRIGHT AND LICENSE>.