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 reccommend
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's usable).
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 .. connect to my database?
61 Once you have created all the appropriate table/source classes, and an
62 overall L<Schema|DBIx::Class::Schema> class, you can start using
63 them in an application. To do this, you need to create a central
64 Schema object, which is used to access all the data in the various
65 tables. See L<DBIx::Class::Schema/connect> for details. The actual
66 connection does not happen until you actually request data, so don't
67 be alarmed if the error from incorrect connection details happens a
70 =item .. use DBIx::Class across multiple databases?
72 If your database server allows you to run querys across multiple
73 databases at once, then so can DBIx::Class. All you need to do is make
74 sure you write the database name as part of the
75 L<DBIx::Class::ResultSource/table> call. Eg:
77 __PACKAGE__->table('mydb.mytablename');
79 And load all the Result classes for both / all databases using one
80 L<DBIx::Class::Schema/load_namespaces> call.
82 =item .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
84 Add the name of the schema to the L<DBIx::Class::ResultSource/table>
85 as part of the name, and make sure you give the one user you are going
86 to connect with rights to read/write all the schemas/tables as
95 =item .. tell DBIx::Class about relationships between my tables?
97 There are a variety of relationship types that come pre-defined for
98 you to use. These are all listed in L<DBIx::Class::Relationship>. If
99 you need a non-standard type, or more information, look in
100 L<DBIx::Class::Relationship::Base>.
102 =item .. define a one-to-many relationship?
104 This is called a C<has_many> relationship on the one side, and a
105 C<belongs_to> relationship on the many side. Currently these need to
106 be set up individually on each side. See L<DBIx::Class::Relationship>
109 =item .. define a relationship where this table contains another table's primary key? (foreign key)
111 Create a C<belongs_to> relationship for the field containing the
112 foreign key. See L<DBIx::Class::Relationship/belongs_to>.
114 =item .. define a foreign key relationship where the key field may contain NULL?
116 Just create a C<belongs_to> relationship, as above. If the column is
117 NULL then the inflation to the foreign object will not happen. This
118 has a side effect of not always fetching all the relevant data, if you
119 use a nullable foreign-key relationship in a JOIN, then you probably
120 want to set the C<join_type> to C<left>.
122 =item .. define a relationship where the key consists of more than one column?
124 Instead of supplying a single column name, all relationship types also
125 allow you to supply a hashref containing the condition across which
126 the tables are to be joined. The condition may contain as many fields
127 as you like. See L<DBIx::Class::Relationship::Base>.
129 =item .. define a relatiopnship across an intermediate table? (many-to-many)
131 Read the documentation on L<DBIx::Class::Relationship/many_to_many>.
133 =item .. stop DBIx::Class from attempting to cascade deletes on my has_many and might_have relationships?
135 By default, DBIx::Class cascades deletes and updates across
136 C<has_many> and C<might_have> relationships. You can disable this
137 behaviour on a per-relationship basis by supplying
138 C<< cascade_delete => 0 >> in the relationship attributes.
140 The cascaded operations are performed after the requested delete or
141 update, so if your database has a constraint on the relationship, it
142 will have deleted/updated the related records or raised an exception
143 before DBIx::Class gets to perform the cascaded operation.
145 See L<DBIx::Class::Relationship>.
147 =item .. use a relationship?
149 Use its name. An accessor is created using the name. See examples in
150 L<DBIx::Class::Manual::Cookbook/Using relationships>.
158 =item .. search for data?
160 Create a C<$schema> object, as mentioned above in ".. connect to my
161 database". Find the L<ResultSet|DBIx::Class::Manual::Glossary/ResultSet>
162 that you want to search in, and call C<search> on it. See
163 L<DBIx::Class::ResultSet/search>.
165 =item .. search using database functions?
167 Supplying something like:
169 ->search({'mydatefield' => 'now()'})
171 to search, will probably not do what you expect. It will quote the
172 text "now()", instead of trying to call the function. To provide
173 literal, unquoted text you need to pass in a scalar reference, like
176 ->search({'mydatefield' => \'now()'})
178 =item .. sort the results of my search?
180 Supply a list of columns you want to sort by to the C<order_by>
181 attribute. See L<DBIx::Class::ResultSet/order_by>.
183 =item .. sort my results based on fields I've aliased using C<as>?
185 You don't. You'll need to supply the same functions/expressions to
186 C<order_by>, as you did to C<select>.
188 To get "fieldname AS alias" in your SQL, you'll need to supply a
189 literal chunk of SQL in your C<select> attribute, such as:
191 ->search({}, { select => [ \'now() AS currenttime'] })
193 Then you can use the alias in your C<order_by> attribute.
195 =item .. group the results of my search?
197 Supply a list of columns you want to group on, to the C<group_by>
198 attribute, see L<DBIx::Class::ResultSet/group_by>.
200 =item .. group my results based on fields I've aliased using C<as>?
202 You don't. You'll need to supply the same functions/expressions to
203 C<group_by>, as you did to C<select>.
205 To get "fieldname AS alias" in your SQL, you'll need to supply a
206 literal chunk of SQL in your C<select> attribute, such as:
208 ->search({}, { select => [ \'now() AS currenttime'] })
210 Then you can use the alias in your C<group_by> attribute.
212 =item .. filter the results of my search?
214 The first argument to C<search> is a hashref of accessor names and
215 values to filter them by, for example:
217 ->search({'created_time' => { '>=', '2006-06-01 00:00:00' } })
219 Note that to use a function here you need to make it a scalar
222 ->search({'created_time' => { '>=', \'yesterday()' } })
224 =item .. search in several tables simultaneously?
226 To search in two related tables, you first need to set up appropriate
227 relationships between their respective classes. When searching you
228 then supply the name of the relationship to the C<join> attribute in
229 your search, for example when searching in the Books table for all the
230 books by the author "Fred Bloggs":
232 ->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors' })
234 The type of join created in your SQL depends on the type of
235 relationship between the two tables, see L<DBIx::Class::Relationship>
236 for the join used by each relationship.
238 =item .. create joins with conditions other than column equality?
240 Currently, L<DBIx::Class> can only create join conditions using
241 equality, so you're probably better off creating a C<view> in your
242 database, and using that as your source. A C<view> is a stored SQL
243 query, which can be accessed similarly to a table, see your database
244 documentation for details.
246 =item .. search with an SQL function on the left hand side?
248 To use an SQL function on the left hand side of a comparison:
250 ->search({ -nest => \[ 'YEAR(date_of_birth) = ?', [ dummy => 1979 ] ] });
252 Or, if you have quoting off:
254 ->search({ 'YEAR(date_of_birth)' => 1979 });
256 =item .. find more help on constructing searches?
258 Behind the scenes, DBIx::Class uses L<SQL::Abstract> to help construct
259 its SQL searches. So if you fail to find help in the
260 L<DBIx::Class::Manual::Cookbook>, try looking in the SQL::Abstract
263 =item .. make searches in Oracle (10gR2 and newer) case-insensitive?
265 To make Oracle behave like most RDBMS use on_connect_do to issue
266 alter session statements on database connection establishment:
268 ->on_connect_do("ALTER SESSION SET NLS_COMP = 'LINGUISTIC'");
269 ->on_connect_do("ALTER SESSION SET NLS_SORT = '<NLS>_CI'");
271 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'BINARY_CI'");
272 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'GERMAN_CI'");
281 =item .. fetch as much data as possible in as few select calls as possible?
283 See the prefetch examples in the L<Cookbook|DBIx::Class::Manual::Cookbook>.
285 =item .. fetch a whole column of data instead of a row?
287 Call C<get_column> on a L<DBIx::Class::ResultSet>. This returns a
288 L<DBIx::Class::ResultSetColumn>. See its documentation and the
289 L<Cookbook|DBIx::Class::Manual::Cookbook> for details.
291 =item .. fetch a formatted column?
293 In your table schema class, create a "private" column accessor with:
295 __PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });
297 Then, in the same class, implement a subroutine called "my_column" that
298 fetches the real value and does the formatting you want.
300 See the Cookbook for more details.
302 =item .. fetch a single (or topmost) row?
304 See L<DBIx::Class::Manual::Cookbook/Retrieve_one_and_only_one_row_from_a_resultset>.
306 A less readable way is to ask a regular search to return 1 row, using
307 L<DBIx::Class::ResultSet/slice>:
309 ->search->(undef, { order_by => "id DESC" })->slice(0)
311 which (if supported by the database) will use LIMIT/OFFSET to hint to the
312 database that we really only need one row. This can result in a significant
313 speed improvement. The method using L<DBIx::Class::ResultSet/single> mentioned
314 in the cookbook can do the same if you pass a C<rows> attribute to the search.
316 =item .. refresh a row from storage?
318 Use L<DBIx::Class::PK/discard_changes>.
320 $row->discard_changes
322 Discarding changes and refreshing from storage are two sides fo the same coin. When you
323 want to discard your local changes, just re-fetch the row from storage. When you want
324 to get a new, fresh copy of the row, just re-fetch the row from storage.
325 L<DBIx::Class::PK/discard_changes> does just that by re-fetching the row from storage
326 using the row's primary key.
328 =item .. fetch my data a "page" at a time?
330 Pass the C<rows> and C<page> attributes to your search, eg:
332 ->search({}, { rows => 10, page => 1});
334 =item .. get a count of all rows even when paging?
336 Call C<pager> on the paged resultset, it will return a L<Data::Page>
337 object. Calling C<total_entries> on the pager will return the correct
340 C<count> on the resultset will only return the total number in the page.
344 =head2 Inserting and updating data
348 =item .. insert a row with an auto incrementing primary key?
350 In versions of L<DBIx::Class> less than 0.07, you need to ensure your
351 table class loads the L<PK::Auto|DBIx::Class::PK::Auto>
352 component. This will attempt to fetch the value of your primary key
353 from the database after the insert has happened, and store it in the
354 created object. In versions 0.07 and above, this component is
355 automatically loaded.
357 =item .. insert a row with a primary key that uses a sequence?
359 You need to create a trigger in your database that updates your
360 primary key field from the sequence. To help PK::Auto find your
361 inserted key, you can tell it the name of the sequence in the
362 C<column_info> supplied with C<add_columns>.
364 ->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });
366 =item .. insert many rows of data efficiently?
368 =item .. update a collection of rows at the same time?
370 Create a resultset using a search, to filter the rows of data you
371 would like to update, then call update on the resultset to change all
374 =item .. use database functions when updating rows?
376 =item .. update a column using data from another column?
378 To stop the column name from being quoted, you'll need to supply a
381 ->update({ somecolumn => \'othercolumn' })
383 But note that when using a scalar reference the column in the database
384 will be updated but when you read the value from the object with e.g.
388 you still get back the scalar reference to the string, B<not> the new
389 value in the database. To get that you must refresh the row from storage
390 using C<discard_changes()>. Or chain your function calls like this:
392 ->update->discard_changes
394 to update the database and refresh the object in one step.
396 =item .. store JSON/YAML in a column and have it deflate/inflate automatically?
398 You can use L<DBIx::Class::InflateColumn> to accomplish YAML/JSON storage transparently.
400 If you want to use JSON, then in your table schema class, do the following:
404 __PACKAGE__->add_columns(qw/ ... my_column ../)
405 __PACKAGE__->inflate_column('my_column', {
406 inflate => sub { jsonToObj(shift) },
407 deflate => sub { objToJson(shift) },
410 For YAML, in your table schema class, do the following:
414 __PACKAGE__->add_columns(qw/ ... my_column ../)
415 __PACKAGE__->inflate_column('my_column', {
416 inflate => sub { YAML::Load(shift) },
417 deflate => sub { YAML::Dump(shift) },
420 This technique is an easy way to store supplemental unstructured data in a table. Be
421 careful not to overuse this capability, however. If you find yourself depending more
422 and more on some data within the inflated column, then it may be time to factor that
431 =item How do I store my own (non-db) data in my DBIx::Class objects?
433 You can add your own data accessors to your classes.
435 One method is to use the built in mk_group_accessors (via L<Class::Accessor::Grouped>)
439 use parent 'DBIx::Class';
441 __PACKAGE__->table('foo'); #etc
442 __PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
444 An another method is to use L<Moose> with your L<DBIx::Class> package.
448 use Moose; # import Moose
449 use Moose::Util::TypeConstraint; # import Moose accessor type constraints
451 extends 'DBIx::Class'; # Moose changes the way we define our parent (base) package
453 has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute
455 __PACKAGE__->table('foo'); # etc
457 With either of these methods the resulting use of the accesssor would be
461 # assume that somewhere in here $row will get assigned to a MyTable row
463 $row->non_column_data('some string'); # would set the non_column_data accessor
465 # some other stuff happens here
467 $row->update(); # would not inline the non_column_data accessor into the update
470 =item How do I use DBIx::Class objects in my TT templates?
472 Like normal objects, mostly. However you need to watch out for TT
473 calling methods in list context. When calling relationship accessors
474 you will not get resultsets, but a list of all the related objects.
476 Starting with version 0.07, you can use L<DBIx::Class::ResultSet/search_rs>
477 to work around this issue.
479 =item See the SQL statements my code is producing?
481 Turn on debugging! See L<DBIx::Class::Storage> for details of how
482 to turn on debugging in the environment, pass your own filehandle to
483 save debug to, or create your own callback.
485 =item Why didn't my search run any SQL?
487 L<DBIx::Class> runs the actual SQL statement as late as possible, thus
488 if you create a resultset using C<search> in scalar context, no query
489 is executed. You can create further resultset refinements by calling
490 search again or relationship accessors. The SQL query is only run when
491 you ask the resultset for an actual row object.
493 =item How do I deal with tables that lack a primary key?
495 If your table lacks a primary key, DBIx::Class can't work out which row
496 it should operate on, for example to delete or update. However, a
497 UNIQUE constraint on one or more columns allows DBIx::Class to uniquely
498 identify the row, so you can tell L<DBIx::Class::ResultSource> these
499 columns act as a primary key, even if they don't from the database's
502 $resultset->set_primary_key(@column);
504 =item How do I make my program start faster?
506 Look at the tips in L<DBIx::Class::Manual::Cookbook/"STARTUP SPEED">
508 =item How do I reduce the overhead of database queries?
510 You can reduce the overhead of object creation within L<DBIx::Class>
511 using the tips in L<DBIx::Class::Manual::Cookbook/"Skip row object creation for faster results">
512 and L<DBIx::Class::Manual::Cookbook/"Get raw data for blindingly fast results">
516 =head2 Notes for CDBI users
520 =item Is there a way to make an object auto-stringify itself as a
521 particular column or group of columns (a-la cdbi Stringfy column
522 group, or stringify_self method) ?
524 See L<DBIx::Class::Manual::Cookbook/Stringification>
528 =head2 Troubleshooting
532 =item Help, I can't connect to postgresql!
534 If you get an error such as:
536 DBI connect('dbname=dbic','user',...) failed: could not connect to server:
537 No such file or directory Is the server running locally and accepting
538 connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
540 Likely you have/had two copies of postgresql installed simultaneously, the
541 second one will use a default port of 5433, while L<DBD::Pg> is compiled with a
542 default port of 5432.
544 You can chance the port setting in C<postgresql.conf>.
546 =item I've lost or forgotten my mysql password
548 Stop mysqld and restart it with the --skip-grant-tables option.
550 Issue the following statements in the mysql client.
552 UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
559 L<http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html>.