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
25 you need to do is to install the DBD 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> or
30 L<http://209.197.234.36/db/simple.html>.
32 Now, decide whether you want to have the database itself be the
33 definitive source of information about the data layout, or your
34 DBIx::Class schema. If it's the former, look up the documentation for
35 your database, eg. L<http://sqlite.org/lang_createtable.html>, on how
36 to create tables, and start creating them. For a nice universal
37 interface to your database, you can try L<DBI::Shell>. If you decided
38 on the latter choice, read the FAQ on setting up your classes
39 manually, and the one on creating tables from your schema.
41 =item .. use DBIx::Class with L<Catalyst>?
43 Install L<Catalyst::Model::DBIC::Schema> from CPAN. See it's
44 documentation, or below, for further details.
46 =item .. set up my DBIx::Class classes automatically from my database?
48 Install L<DBIx::Class::Schema::Loader> from CPAN, and read it's documentation.
50 =item .. set up my DBIx::Class classes manually?
52 Look at the L<DBIx::Class::Manual::Example>, come back here if you get lost.
54 =item .. create my database tables from my DBIx::Class schema?
56 Create your classes manually, as above. Write a script that calls
57 L<DBIx::Class::Schema/deploy>. See there for details, or the
58 L<DBIx::Class::Manual::Cookbook>.
60 =item .. connect to my database?
62 Once you have created all the appropriate table/source classes, and an
63 overall L<Schema|DBIx::Class::Schema> class, you can start using
64 them in an application. To do this, you need to create a central
65 Schema object, which is used to access all the data in the various
66 tables. See L<DBIx::Class::Schema/connect> for details. The actual
67 connection does not happen until you actually request data, so don't
68 be alarmed if the error from incorrect connection details happens a
78 =item .. tell DBIx::Class about relationships between my tables?
80 There are a vareity of relationship types that come pre-defined for you to use. These are all listed in L<DBIx::Class::Relationship>. If you need a non-standard type, or more information, look in L<DBIx::Class::Relationship::Base>.
82 =item .. define a one-to-many relationship?
84 This is called a C<has_many> relationship on the one side, and a C<belongs_to> relationship on the many side. Currently these need to be set up individually on each side. See L<DBIx::Class::Relationship> for details.
86 =item .. define a relationship where this table contains another table's primary key? (foreign key)
88 Create a C<belongs_to> relationship for the field containing the foreign key. L<DBIx::Class::Relationship/belongs_to>.
90 =item .. define a foreign key relationship where the key field may contain NULL?
92 Just create a C<belongs_to> relationship, as above. If
93 the column is NULL then the inflation to the foreign object will not
94 happen. This has a side effect of not always fetching all the relevant
95 data, if you use a nullable foreign-key relationship in a JOIN, then
96 you probably want to set the join_type to 'left'.
98 =item .. define a relationship where the key consists of more than one column?
100 Instead of supplying a single column name, all relationship types also
101 allow you to supply a hashref containing the condition across which
102 the tables are to be joined. The condition may contain as many fields
103 as you like. See L<DBIx::Class::Relationship::Base>.
105 =item .. define a relatiopnship across an intermediate table? (many-to-many)
107 Read the documentation on L<DBIx::Class::Relationship/many_to_many>.
109 =item .. stop DBIx::Class from attempting to cascade deletes on my has_many relationships?
111 By default, DBIx::Class cascades deletes and updates across
112 C<has_many> relationships. If your database already does this (and
113 probably better), turn it off by supplying C<< cascade_delete => 0 >> in
114 the relationship attributes. See L<DBIx::Class::Relationship::Base>.
116 =item .. use a relationship?
118 Use it's name. An accessor is created using the name. See examples in L<DBIx::Class::Manual::Cookbook/Using relationships>.
126 =item .. search for data?
128 Create a C<$schema> object, as mentioned above in ".. connect to my
130 L<ResultSet|DBIx::Class::Manual::Glossary/ResultSet> that you want
131 to search in, and call C<search> on it. See
132 L<DBIx::Class::ResultSet/search>.
134 =item .. search using database functions?
136 Supplying something like:
138 ->search({'mydatefield' => 'now()'})
140 to search, will probably not do what you expect. It will quote the
141 text "now()", instead of trying to call the function. To provide
142 literal, unquoted text you need to pass in a scalar reference, like
145 ->search({'mydatefield' => \'now()'})
147 =item .. sort the results of my search?
149 Supply a list of columns you want to sort by, to the C<order_by>
150 attribute, see L<DBIx::Class::ResultSet/order_by>.
152 =item .. sort my results based on fields I've aliased using C<as>?
154 You don't. You'll need to supply the same functions/expressions to
155 C<order_by>, as you did to C<select>.
157 To get "fieldname AS alias" in your SQL, you'll need to supply a literal chunk of SQL in your C<select> attribute, such as:
159 ->search({}, { select => [ \'now() AS currenttime'] })
161 Then you can use the alias in your C<order_by> attribute.
163 =item .. group the results of my search?
165 Supply a list of columns you want to group on, to the C<group_by>
166 attribute, see L<DBIx::Class::ResultSet/group_by>.
168 =item .. group my results based on fields I've aliased using C<as>?
170 You don't. You'll need to supply the same functions/expressions to
171 C<group_by>, as you did to C<select>.
173 To get "fieldname AS alias" in your SQL, you'll need to supply a
174 literal chunk of SQL in your C<select> attribute, such as:
176 ->search({}, { select => [ \'now() AS currenttime'] })
178 Then you can use the alias in your C<group_by> attribute.
180 =item .. filter the results of my search?
182 The first argument to C<search> is a hashref of accessor names and
183 values to filter them by, for example:
185 ->search({'created_time' => { '>=', '2006-06-01 00:00:00'} })
187 Note that to use a function here you need to make the whole value into
190 ->search({'created_time' => \'>= yesterday() })
192 =item .. search in several tables simultaneously?
194 To search in two related tables, you first need to set up appropriate
195 relationships between their respective classes. When searching you
196 then supply the name of the relationship to the C<join> attribute in
197 your search, for example when searching in the Books table for all the
198 books by the author "Fred Bloggs":
200 ->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors'})
202 The type of join created in your SQL depends on the type of
203 relationship between the two tables, see L<DBIx::Class::Relationship>
204 for the join used by each relationship.
206 =item .. create joins with conditions other than column equality?
208 Currently, L<DBIx::Class> can only create join conditions using
209 equality, so you're probably better off creating a C<view> in your
210 database, and using that as your source. A C<view> is a stored SQL query,
211 which can be accessed similarly to a table, see your database
212 documentation for details.
214 =item .. search using greater-than or less-than and database functions?
216 To use functions or literal SQL with conditions other than equality
217 you need to supply the entire condition, for example:
219 my $interval = "< now() - interval '12 hours'";
220 ->search({last_attempt => \$interval})
224 my $interval = "now() - interval '12 hours'";
225 ->search({last_attempt => { '<' => \$interval } })
227 =item .. find more help on constructing searches?
229 Behind the scenes, DBIx::Class uses L<SQL::Abstract> to help construct
230 it's SQL searches. So if you fail to find help in the
231 L<DBIx::Class::Manual::Cookbook>, try looking in the SQL::Abstract
240 =item .. fetch as much data as possible in as few select calls as possible? (prefetch)
242 See the prefetch examples in the L<Cookbook|DBIx::Class::Manual::Cookbook>.
246 =head2 Inserting and updating data
250 =item .. insert a row with an auto incrementing primary key?
252 In versions of L<DBIx::Class> less than 0.07, you need to ensure your
253 table class loads the L<PK::Auto|DBIx::Class::PK::Auto>
254 component. This will attempt to fetch the value of your primary key
255 from the database after the insert has happened, and store it in the
256 created object. In versions 0.07 and above, this component is
257 automatically loaded.
259 =item .. insert a row with a primary key that uses a sequence?
261 You need to create a trigger in your database that updates your
262 primary key field from the sequence. To help PK::Auto find your
263 inserted key, you can tell it the name of the sequence in the
264 C<column_info> supplied with C<add_columns>.
266 ->add_columns({ id => { sequence => 'mysequence' } });
268 =item .. insert many rows of data efficiently?
270 =item .. update a collection of rows at the same time?
272 Create a resultset using a search, to filter the rows of data you
273 would like to update, then call update on the resultset to change all
276 =item .. use database functions when updating rows?
278 =item .. update a column using data from another column?
280 To stop the column name from being quoted, you'll need to supply a
283 ->update({ somecolumn => '\othercolumn'})
291 =item How do I store my own (non-db) data in my DBIx::Class objects?
293 You can add your own data accessors to your classes.
295 =item How do I use DBIx::Class objects in my TT templates?
297 Like normal objects, mostly. However you need to watch out for TTs
298 calling methods in list context, this means that when calling
299 relationship accessors you will not get resultsets, but a list of all
302 =item See the SQL statements my code is producing?
304 Turn on debugging! See L<DBIx::Class::Storage::DBI> for details of how
305 to turn on debugging in the environment, pass your own filehandle to
306 save debug to, or create your own callback.
308 =item Why didn't my search run any SQL?
310 L<DBIx::Class> runs the actual SQL statement as late as possible, thus
311 if you create a resultset using C<search> in scalar context, no query
312 is executed. You can create further resultset refinements by calling
313 search again or relationship accessors. The SQL query is only run when
314 you ask the resultset for an actual Row object.