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 querys 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<DBIx::Class::ResultSource/table> call. Eg:
83 __PACKAGE__->table('mydb.mytablename');
85 And load all the Result classes for both / all databases using one
86 L<DBIx::Class::Schema/load_namespaces> call.
88 =item .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
90 Add the name of the schema to the L<DBIx::Class::ResultSource/table>
91 as part of the name, and make sure you give the one user you are going
92 to connect with has permissions to read/write all the schemas/tables as
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'");
272 =item .. fetch as much data as possible in as few select calls as possible?
274 See the prefetch examples in the L<Cookbook|DBIx::Class::Manual::Cookbook>.
276 =item .. fetch a whole column of data instead of a row?
278 Call C<get_column> on a L<DBIx::Class::ResultSet>. This returns a
279 L<DBIx::Class::ResultSetColumn>. See its documentation and the
280 L<Cookbook|DBIx::Class::Manual::Cookbook> for details.
282 =item .. fetch a formatted column?
284 In your table schema class, create a "private" column accessor with:
286 __PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });
288 Then, in the same class, implement a subroutine called "my_column" that
289 fetches the real value and does the formatting you want.
291 See the L<Cookbook|DBIx::Class::Manual::Cookbook> for more details.
293 =item .. fetch a single (or topmost) row?
295 Use the L<DBIx::Class::ResultSet/rows> and
296 L<DBIx::Class::ResultSet/order_by> attributes to order your data and
297 pick off a single row.
299 See also L<DBIx::Class::Manual::Cookbook/Retrieve one and only one row from a resultset>.
301 A less readable way is to ask a regular search to return 1 row, using
302 L<DBIx::Class::ResultSet/slice>:
304 ->search->(undef, { order_by => "id DESC" })->slice(0)
306 which (if supported by the database) will use LIMIT/OFFSET to hint to the
307 database that we really only need one row. This can result in a significant
308 speed improvement. The method using L<DBIx::Class::ResultSet/single> mentioned
309 in the cookbook can do the same if you pass a C<rows> attribute to the search.
311 =item .. refresh a row from storage?
313 Use L<DBIx::Class::Row/discard_changes>.
315 $row->discard_changes
317 Discarding changes and refreshing from storage are two sides fo the same coin. When you
318 want to discard your local changes, just re-fetch the row from storage. When you want
319 to get a new, fresh copy of the row, just re-fetch the row from storage.
320 L<DBIx::Class::Row/discard_changes> does just that by re-fetching the row from storage
321 using the row's primary key.
323 =item .. fetch my data a "page" at a time?
325 Pass the C<rows> and C<page> attributes to your search, eg:
327 ->search({}, { rows => 10, page => 1});
329 =item .. get a count of all rows even when paging?
331 Call C<pager> on the paged resultset, it will return a L<Data::Page>
332 object. Calling C<total_entries> on the pager will return the correct
335 C<count> on the resultset will only return the total number in the page.
339 =head2 Inserting and updating data
343 =item .. insert a row with an auto incrementing primary key?
345 This happens automatically. After
346 L<creating|DBIx::Class::ResultSet/create> a result object, the primary
347 key value created by your database can be fetched by calling C<id> (or
348 the access of your primary key column) on the object.
350 =item .. insert a row with a primary key that uses a sequence?
352 You need to create a trigger in your database that updates your
353 primary key field from the sequence. To help PK::Auto find the next
354 key value, you can tell it the name of the sequence in the
355 C<column_info> supplied with C<add_columns>.
357 ->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });
359 =item .. insert many rows of data efficiently?
361 The C<populate> method in L<DBIx::Class::ResultSet> provides
362 efficient bulk inserts.
364 L<DBIx::Class::Fixtures> provides an alternative way to do this.
366 =item .. update a collection of rows at the same time?
368 Create a resultset using a C<search>, to filter the rows of data you
369 would like to update, then call C<update> on the resultset to change all
372 =item .. use database functions when updating rows?
374 =item .. update a column using data from another column?
376 To stop the column name from being quoted, you'll need to tell DBIC
377 that the right hand side is an SQL identifier (it will be quoted
378 properly if you have quoting enabled):
380 ->update({ somecolumn => { -ident => 'othercolumn' } })
382 This method will not retrieve the new value and put it in your Row
383 object. To fetch the new value, use the C<discard_changes> method on
386 # will return the scalar reference:
389 # issue a select using the PK to re-fetch the row data:
390 $row->discard_changes();
392 # Now returns the correct new value:
395 To update and refresh at once, chain your calls:
397 $row->update({ 'somecolumn' => { -ident => 'othercolumn' } })->discard_changes;
399 =item .. store JSON/YAML in a column and have it deflate/inflate automatically?
401 You can use L<DBIx::Class::InflateColumn> to accomplish YAML/JSON storage transparently.
403 If you want to use JSON, then in your table schema class, do the following:
407 __PACKAGE__->add_columns(qw/ ... my_column ../)
408 __PACKAGE__->inflate_column('my_column', {
409 inflate => sub { jsonToObj(shift) },
410 deflate => sub { objToJson(shift) },
413 For YAML, in your table schema class, do the following:
417 __PACKAGE__->add_columns(qw/ ... my_column ../)
418 __PACKAGE__->inflate_column('my_column', {
419 inflate => sub { YAML::Load(shift) },
420 deflate => sub { YAML::Dump(shift) },
423 This technique is an easy way to store supplemental unstructured data in a table. Be
424 careful not to overuse this capability, however. If you find yourself depending more
425 and more on some data within the inflated column, then it may be time to factor that
430 =head2 Custom methods in Result classes
432 You can add custom methods that do arbitrary things, even to unrelated tables.
433 For example, to provide a C<< $book->foo() >> method which searches the
434 cd table, you'd could add this to Book.pm:
437 my ($self, $col_data) = @_;
438 return $self->result_source->schema->resultset('cd')->search($col_data);
441 And invoke that on any Book Result object like so:
443 my $rs = $book->foo({ title => 'Down to Earth' });
445 When two tables ARE related, L<DBIx::Class::Relationship::Base> provides many
446 methods to find or create data in related tables for you. But if you want to
447 write your own methods, you can.
449 For example, to provide a C<< $book->foo() >> method to manually implement
450 what create_related() from L<DBIx::Class::Relationship::Base> does, you could
454 my ($self, $relname, $col_data) = @_;
455 return $self->related_resultset($relname)->create($col_data);
460 my $author = $book->foo('author', { name => 'Fred' });
466 =item How do I store my own (non-db) data in my DBIx::Class objects?
468 You can add your own data accessors to your Result classes.
470 One method is to use the built in mk_group_accessors (via L<Class::Accessor::Grouped>)
472 package App::Schema::Result::MyTable;
474 use parent 'DBIx::Class::Core';
476 __PACKAGE__->table('foo'); #etc
477 __PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
479 An another method is to use L<Moose> with your L<DBIx::Class> package.
481 package App::Schema::Result::MyTable;
483 use Moose; # import Moose
484 use Moose::Util::TypeConstraint; # import Moose accessor type constraints
486 extends 'DBIx::Class::Core'; # Moose changes the way we define our parent (base) package
488 has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute
490 __PACKAGE__->table('foo'); # etc
492 With either of these methods the resulting use of the accesssor would be
496 # assume that somewhere in here $row will get assigned to a MyTable row
498 $row->non_column_data('some string'); # would set the non_column_data accessor
500 # some other stuff happens here
502 $row->update(); # would not inline the non_column_data accessor into the update
505 =item How do I use DBIx::Class objects in my TT templates?
507 Like normal objects, mostly. However you need to watch out for TT
508 calling methods in list context. When calling relationship accessors
509 you will not get resultsets, but a list of all the related objects.
511 Use the L<DBIx::Class::ResultSet/search_rs> method, or the
512 relationship accessor methods ending with "_rs" to work around this
515 See also L<DBIx::Class::Relationship/has_many>.
517 =item See the SQL statements my code is producing?
519 Set the shell environment variable C<DBIC_TRACE> to a true value.
521 For more info see L<DBIx::Class::Storage> for details of how
522 to turn on debugging in the environment, pass your own filehandle to
523 save debug to, or create your own callback.
525 =item Why didn't my search run any SQL?
527 L<DBIx::Class> runs the actual SQL statement as late as possible, thus
528 if you create a resultset using C<search> in scalar context, no query
529 is executed. You can create further resultset refinements by calling
530 search again or relationship accessors. The SQL query is only run when
531 you ask the resultset for an actual result object.
533 =item How do I deal with tables that lack a primary key?
535 If your table lacks a primary key, DBIx::Class can't work out which row
536 it should operate on, for example to delete or update. However, a
537 UNIQUE constraint on one or more columns allows DBIx::Class to uniquely
538 identify the row, so you can tell L<DBIx::Class::ResultSource> these
539 columns act as a primary key, even if they don't from the database's
542 $resultset->set_primary_key(@column);
544 =item How do I make my program start faster?
546 Look at the tips in L<DBIx::Class::Manual::Cookbook/"STARTUP SPEED">
548 =item How do I reduce the overhead of database queries?
550 You can reduce the overhead of object creation within L<DBIx::Class>
551 using the tips in L<DBIx::Class::Manual::Cookbook/"Skip result object creation for faster results">
552 and L<DBIx::Class::Manual::Cookbook/"Get raw data for blindingly fast results">
554 =item How do I override a run time method (e.g. a relationship accessor)?
556 If you need access to the original accessor, then you must "wrap around" the original method.
557 You can do that either with L<Moose::Manual::MethodModifiers> or L<Class::Method::Modifiers>.
558 The code example works for both modules:
560 package Your::Schema::Group;
561 use Class::Method::Modifiers;
563 # ... declare columns ...
565 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
566 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
568 # if the server group is a "super group", then return all servers
569 # otherwise return only servers that belongs to the given group
570 around 'servers' => sub {
574 return $self->$orig(@_) unless $self->is_super_group;
575 return $self->result_source->schema->resultset('Server')->all;
578 If you just want to override the original method, and don't care about the data
579 from the original accessor, then you have two options. Either use
580 L<Method::Signatures::Simple> that does most of the work for you, or do
583 L<Method::Signatures::Simple> way:
585 package Your::Schema::Group;
586 use Method::Signatures::Simple;
588 # ... declare columns ...
590 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
591 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
593 # The method keyword automatically injects the annoying my $self = shift; for you.
595 return $self->result_source->schema->resultset('Server')->search({ ... });
600 package Your::Schema::Group;
603 # ... declare columns ...
605 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
606 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
608 *servers = subname servers => sub {
610 return $self->result_source->schema->resultset('Server')->search({ ... });
615 =head2 Notes for CDBI users
619 =item Is there a way to make an object auto-stringify itself as a
620 particular column or group of columns (a-la cdbi Stringfy column
621 group, or stringify_self method) ?
623 See L<DBIx::Class::Manual::Cookbook/Stringification>
627 =head2 Troubleshooting
631 =item Help, I can't connect to postgresql!
633 If you get an error such as:
635 DBI connect('dbname=dbic','user',...) failed: could not connect to server:
636 No such file or directory Is the server running locally and accepting
637 connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
639 Likely you have/had two copies of postgresql installed simultaneously, the
640 second one will use a default port of 5433, while L<DBD::Pg> is compiled with a
641 default port of 5432.
643 You can change the port setting in C<postgresql.conf>.
645 =item I've lost or forgotten my mysql password
647 Stop mysqld and restart it with the --skip-grant-tables option.
649 Issue the following statements in the mysql client.
651 UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
658 L<http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html>.