1DBIx::Class::Manual::FAUQs(e3r)Contributed Perl DocumentDaBtIixo:n:Class::Manual::FAQ(3)
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6 DBIx::Class::Manual::FAQ - Frequently Asked Questions (in theory)
7
9 This document is intended as an anti-map of the documentation. If you
10 know what you want to do, but not how to do it in DBIx::Class, then
11 look here. It does not contain much code or examples, it just gives
12 explanations and pointers to the correct pieces of documentation to
13 read.
14
16 How Do I:
17 Getting started
19 .. create a database to use?
20 First, choose a database. For testing/experimenting, we recommend
21 DBD::SQLite, which is a self-contained small database (i.e. all you
22 need to do is to install DBD::SQLite from CPAN, and it works).
23 Next, spend some time defining which data you need to store, and
25 how it relates to the other data you have. For some help on
26 normalisation, go to <http://b62.tripod.com/doc/dbbase.htm>.
27 Now, decide whether you want to have the database itself be the
29 definitive source of information about the data layout, or your
30 DBIx::Class schema. If it's the former, look up the documentation
31 for your database, eg. <http://sqlite.org/lang_createtable.html>,
32 on how to create tables, and start creating them. For a nice
33 universal interface to your database, you can try DBI::Shell. If
34 you decided on the latter choice, read the FAQ on setting up your
35 classes manually, and the one on creating tables from your schema.
36 .. use DBIx::Class with Catalyst?
38 Install Catalyst::Model::DBIC::Schema from CPAN. See its
39 documentation, or below, for further details.
40 .. set up my DBIx::Class classes automatically from my database?
42 Install DBIx::Class::Schema::Loader from CPAN, and read its
43 documentation.
44 .. set up my DBIx::Class classes manually?
46 Look at the DBIx::Class::Manual::Example and come back here if you
47 get lost.
48 .. create my database tables from my DBIx::Class schema?
50 Create your classes manually, as above. Write a script that calls
51 "deploy" in DBIx::Class::Schema. See there for details, or the
52 DBIx::Class::Manual::Cookbook.
53 .. store/retrieve Unicode data in my database?
55 Make sure you database supports Unicode and set the connect
56 attributes appropriately - see "Using Unicode" in
57 DBIx::Class::Manual::Cookbook
58 .. connect to my database?
60 Once you have created all the appropriate table/source classes, and
61 an overall Schema class, you can start using them in an
62 application. To do this, you need to create a central Schema
63 object, which is used to access all the data in the various tables.
64 See "connect" in DBIx::Class::Schema for details. The actual
65 connection does not happen until you actually request data, so
66 don't be alarmed if the error from incorrect connection details
67 happens a lot later.
68 .. use DBIx::Class across multiple databases?
70 If your database server allows you to run queries across multiple
71 databases at once, then so can DBIx::Class. All you need to do is
72 make sure you write the database name as part of the table call.
73 Eg:
74 __PACKAGE__->table('mydb.mytablename');
76 And load all the Result classes for both / all databases by calling
78 "load_namespaces" in DBIx::Class::Schema.
79 .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
81 Add the name of the schema to the table name, when invoking table,
82 and make sure the user you are about to connect as has permissions
83 to read/write all the schemas/tables as necessary.
84 Relationships
86 .. tell DBIx::Class about relationships between my tables?
87 There are a variety of relationship types that come pre-defined for
88 you to use. These are all listed in DBIx::Class::Relationship. If
89 you need a non-standard type, or more information, look in
90 DBIx::Class::Relationship::Base.
91 .. define a one-to-many relationship?
93 This is called a "has_many" relationship on the one side, and a
94 "belongs_to" relationship on the many side. Currently these need to
95 be set up individually on each side. See DBIx::Class::Relationship
96 for details.
97 .. define a relationship where this table contains another table's
99 primary key? (foreign key)
100 Create a "belongs_to" relationship for the field containing the
101 foreign key. See "belongs_to" in DBIx::Class::Relationship.
102 .. define a foreign key relationship where the key field may contain
104 NULL?
105 Just create a "belongs_to" relationship, as above. If the column is
106 NULL then the inflation to the foreign object will not happen. This
107 has a side effect of not always fetching all the relevant data, if
108 you use a nullable foreign-key relationship in a JOIN, then you
109 probably want to set the "join_type" to "left".
110 .. define a relationship where the key consists of more than one
112 column?
113 Instead of supplying a single column name, all relationship types
114 also allow you to supply a hashref containing the condition across
115 which the tables are to be joined. The condition may contain as
116 many fields as you like. See DBIx::Class::Relationship::Base.
117 .. define a relationship bridge across an intermediate table? (many-to-
119 many)
120 The term 'relationship' is used loosely with many_to_many as it is
121 not considered a relationship in the fullest sense. For more info,
122 read the documentation on "many_to_many" in
123 DBIx::Class::Relationship.
124 .. stop DBIx::Class from attempting to cascade deletes on my has_many
126 and might_have relationships?
127 By default, DBIx::Class cascades deletes and updates across
128 "has_many" and "might_have" relationships. You can disable this
129 behaviour on a per-relationship basis by supplying "cascade_delete
130 => 0" in the relationship attributes.
131 The cascaded operations are performed after the requested delete or
133 update, so if your database has a constraint on the relationship,
134 it will have deleted/updated the related records or raised an
135 exception before DBIx::Class gets to perform the cascaded
136 operation.
137 See DBIx::Class::Relationship.
139 .. use a relationship?
141 Use its name. An accessor is created using the name. See examples
142 in "USING RELATIONSHIPS" in DBIx::Class::Manual::Cookbook.
143 Searching
145 .. search for data?
146 Create a $schema object, as mentioned above in ".. connect to my
147 database?". Find the ResultSet that you want to search in, by
148 calling "$schema->resultset('MySource')" and call "search" on it.
149 See "search" in DBIx::Class::ResultSet.
150 .. search using database functions?
152 Supplying something like:
153 ->search({'mydatefield' => 'now()'})
155 to search, will probably not do what you expect. It will quote the
157 text "now()", instead of trying to call the function. To provide
158 literal, unquoted text you need to pass in a scalar reference, like
159 so:
160 ->search({'mydatefield' => \'now()'})
162 .. sort the results of my search?
164 Supply a list of columns you want to sort by to the "order_by"
165 attribute. See "order_by" in DBIx::Class::ResultSet.
166 .. sort my results based on fields I've aliased using "as"?
168 You didn't alias anything, since as has nothing to do with the
169 produced SQL. See "select" in DBIx::Class::ResultSet for details.
170 .. group the results of my search?
172 Supply a list of columns you want to group on, to the "group_by"
173 attribute, see "group_by" in DBIx::Class::ResultSet.
174 .. group my results based on fields I've aliased using "as"?
176 You don't. See the explanation on ordering by an alias above.
177 .. filter the results of my search?
179 The first argument to "search" is a hashref of accessor names and
180 values to filter them by, for example:
181 ->search({'created_time' => { '>=', '2006-06-01 00:00:00' } })
183 Note that to use a function here you need to make it a scalar
185 reference:
186 ->search({'created_time' => { '>=', \'yesterday()' } })
188 .. search in several tables simultaneously?
190 To search in two related tables, you first need to set up
191 appropriate relationships between their respective classes. When
192 searching you then supply the name of the relationship to the
193 "join" attribute in your search, for example when searching in the
194 Books table for all the books by the author "Fred Bloggs":
195 ->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors' })
197 The type of join created in your SQL depends on the type of
199 relationship between the two tables, see DBIx::Class::Relationship
200 for the join used by each relationship.
201 .. create joins with conditions other than column equality?
203 Currently, DBIx::Class can only create join conditions using
204 equality, so you're probably better off creating a "view" in your
205 database, and using that as your source. A "view" is a stored SQL
206 query, which can be accessed similarly to a table, see your
207 database documentation for details.
208 .. search with an SQL function on the left hand side?
210 To use an SQL function on the left hand side of a comparison you
211 currently need to resort to literal SQL:
212 ->search( \[ 'YEAR(date_of_birth) = ?', 1979 ] );
214 .. find more help on constructing searches?
216 Behind the scenes, DBIx::Class uses SQL::Abstract::Classic to help
217 construct its SQL searches. So if you fail to find help in the
218 DBIx::Class::Manual::Cookbook, try looking in the
219 SQL::Abstract::Classic documentation.
220 .. make searches in Oracle (10gR2 and newer) case-insensitive?
222 To make Oracle behave like most RDBMS use on_connect_do to issue
223 alter session statements on database connection establishment:
224 ->on_connect_do("ALTER SESSION SET NLS_COMP = 'LINGUISTIC'");
226 ->on_connect_do("ALTER SESSION SET NLS_SORT = '<NLS>_CI'");
227 e.g.
228 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'BINARY_CI'");
229 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'GERMAN_CI'");
230 .. format a DateTime object for searching?
232 search and find do not take DBIx::Class::InflateColumn into
233 account, and so your DateTime object will not be correctly deflated
234 into a format your RDBMS expects.
235 The datetime_parser method on your storage object can be used to
237 return the object that would normally do this, so it's easy to do
238 it manually:
239 my $dtf = $schema->storage->datetime_parser;
241 my $rs = $schema->resultset('users')->search(
242 {
243 signup_date => {
244 -between => [
245 $dtf->format_datetime($dt_start),
246 $dtf->format_datetime($dt_end),
247 ],
248 }
249 },
250 );
251 With in a Result Class method, you can get this from the
253 "result_source".
254 my $dtf = $self->result_source->storage->datetime_parser;
256 This kludge is necessary only for conditions passed to search and
258 "find" in DBIx::Class::ResultSet, whereas create and "update" in
259 DBIx::Class::Row (but not "update" in DBIx::Class::ResultSet) are
260 DBIx::Class::InflateColumn-aware and will do the right thing when
261 supplied an inflated DateTime object.
262 Fetching data
264 .. fetch as much data as possible in as few select calls as possible?
265 See the prefetch examples in the Cookbook.
266 .. fetch a whole column of data instead of a row?
268 Call "get_column" on a DBIx::Class::ResultSet. This returns a
269 DBIx::Class::ResultSetColumn. See its documentation and the
270 Cookbook for details.
271 .. fetch a formatted column?
273 In your table schema class, create a "private" column accessor
274 with:
275 __PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });
277 Then, in the same class, implement a subroutine called "my_column"
279 that fetches the real value and does the formatting you want.
280 See the Cookbook for more details.
282 .. fetch a single (or topmost) row?
284 Use the "rows" in DBIx::Class::ResultSet and "order_by" in
285 DBIx::Class::ResultSet attributes to order your data and pick off a
286 single row.
287 See also "Retrieve one and only one row from a resultset" in
289 DBIx::Class::Manual::Cookbook.
290 A less readable way is to ask a regular search to return 1 row,
292 using "slice" in DBIx::Class::ResultSet:
293 ->search->(undef, { order_by => "id DESC" })->slice(0)
295 which (if supported by the database) will use LIMIT/OFFSET to hint
297 to the database that we really only need one row. This can result
298 in a significant speed improvement. The method using "single" in
299 DBIx::Class::ResultSet mentioned in the cookbook can do the same if
300 you pass a "rows" attribute to the search.
301 .. refresh a row from storage?
303 Use "discard_changes" in DBIx::Class::Row.
304 $result->discard_changes
306 Discarding changes and refreshing from storage are two sides of the
308 same coin. When you want to discard your local changes, just re-
309 fetch the row from storage. When you want to get a new, fresh copy
310 of the row, just re-fetch the row from storage. "discard_changes"
311 in DBIx::Class::Row does just that by re-fetching the row from
312 storage using the row's primary key.
313 .. fetch my data a "page" at a time?
315 Pass the "rows" and "page" attributes to your search, eg:
316 ->search({}, { rows => 10, page => 1});
318 .. get a count of all rows even when paging?
320 Call "pager" on the paged resultset, it will return a pager object
321 with an API/behavior identical to that of Data::Page from late
322 2009 through late 2019
323 <https://metacpan.org/pod/release/LBROCARD/Data-
324 Page-2.02/lib/Data/Page.pm>. Calling "total_entries" on the pager
325 will return the correct total.
326 "count" on the resultset will only return the total number in the
328 page.
329 Inserting and updating data
331 .. insert a row with an auto incrementing primary key?
332 This happens automatically. After creating a result object, the
333 primary key value created by your database can be fetched by
334 calling "id" (or the access of your primary key column) on the
335 object.
336 .. insert a row with a primary key that uses a sequence?
338 You need to create a trigger in your database that updates your
339 primary key field from the sequence. To help PK::Auto find the next
340 key value, you can tell it the name of the sequence in the
341 "column_info" supplied with "add_columns".
342 ->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });
344 .. insert many rows of data efficiently?
346 The "populate" method in DBIx::Class::ResultSet provides efficient
347 bulk inserts.
348 DBIx::Class::Fixtures provides an alternative way to do this.
350 .. update a collection of rows at the same time?
352 Create a resultset using a "search", to filter the rows of data you
353 would like to update, then call "update" on the resultset to change
354 all the rows at once.
355 .. use database functions when updating rows?
357 .. update a column using data from another column?
358 To stop the column name from being quoted, you'll need to tell DBIC
359 that the right hand side is an SQL identifier (it will be quoted
360 properly if you have quoting enabled):
361 ->update({ somecolumn => { -ident => 'othercolumn' } })
363 This method will not retrieve the new value and put it in your Row
365 object. To fetch the new value, use the "discard_changes" method on
366 the Row.
367 # will return the scalar reference:
369 $result->somecolumn()
370 # issue a select using the PK to re-fetch the row data:
372 $result->discard_changes();
373 # Now returns the correct new value:
375 $result->somecolumn()
376 To update and refresh at once, chain your calls:
378 $result->update({ 'somecolumn' => { -ident => 'othercolumn' } })->discard_changes;
380 .. store JSON/YAML in a column and have it deflate/inflate
382 automatically?
383 You can use DBIx::Class::InflateColumn to accomplish YAML/JSON
384 storage transparently.
385 If you want to use JSON, then in your table schema class, do the
387 following:
388 use JSON;
390 __PACKAGE__->add_columns(qw/ ... my_column ../)
392 __PACKAGE__->inflate_column('my_column', {
393 inflate => sub { jsonToObj(shift) },
394 deflate => sub { objToJson(shift) },
395 });
396 For YAML, in your table schema class, do the following:
398 use YAML;
400 __PACKAGE__->add_columns(qw/ ... my_column ../)
402 __PACKAGE__->inflate_column('my_column', {
403 inflate => sub { YAML::Load(shift) },
404 deflate => sub { YAML::Dump(shift) },
405 });
406 This technique is an easy way to store supplemental unstructured
408 data in a table. Be careful not to overuse this capability,
409 however. If you find yourself depending more and more on some data
410 within the inflated column, then it may be time to factor that data
411 out.
412 Custom methods in Result classes
414 You can add custom methods that do arbitrary things, even to unrelated
415 tables. For example, to provide a "$book->foo()" method which searches
416 the cd table, you'd could add this to Book.pm:
417 sub foo {
419 my ($self, $col_data) = @_;
420 return $self->result_source->schema->resultset('cd')->search($col_data);
421 }
422 And invoke that on any Book Result object like so:
424 my $rs = $book->foo({ title => 'Down to Earth' });
426 When two tables ARE related, DBIx::Class::Relationship::Base provides
428 many methods to find or create data in related tables for you. But if
429 you want to write your own methods, you can.
430 For example, to provide a "$book->foo()" method to manually implement
432 what create_related() from DBIx::Class::Relationship::Base does, you
433 could add this to Book.pm:
434 sub foo {
436 my ($self, $rel_name, $col_data) = @_;
437 return $self->related_resultset($rel_name)->create($col_data);
438 }
439 Invoked like this:
441 my $author = $book->foo('author', { name => 'Fred' });
443 Misc
445 How do I store my own (non-db) data in my DBIx::Class objects?
446 You can add your own data accessors to your Result classes.
447 One method is to use the built in mk_group_accessors (via
449 Class::Accessor::Grouped)
450 package App::Schema::Result::MyTable;
452 use parent 'DBIx::Class::Core';
454 __PACKAGE__->table('foo'); #etc
456 __PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
457 And another method is to use Moose with your DBIx::Class package.
459 package App::Schema::Result::MyTable;
461 use Moose; # import Moose
463 use Moose::Util::TypeConstraint; # import Moose accessor type constraints
464 extends 'DBIx::Class::Core'; # Moose changes the way we define our parent (base) package
466 has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute
468 __PACKAGE__->table('foo'); # etc
470 With either of these methods the resulting use of the accessor
472 would be
473 my $result;
475 # assume that somewhere in here $result will get assigned to a MyTable row
477 $result->non_column_data('some string'); # would set the non_column_data accessor
479 # some other stuff happens here
481 $result->update(); # would not inline the non_column_data accessor into the update
483 How do I use DBIx::Class objects in my TT templates?
485 Like normal objects, mostly. However you need to watch out for TT
486 calling methods in list context. When calling relationship
487 accessors you will not get resultsets, but a list of all the
488 related objects.
489 Use the "search_rs" in DBIx::Class::ResultSet method, or the
491 relationship accessor methods ending with "_rs" to work around this
492 issue.
493 See also "has_many" in DBIx::Class::Relationship.
495 See the SQL statements my code is producing?
497 Set the shell environment variable "DBIC_TRACE" to a true value.
498 For more info see DBIx::Class::Storage for details of how to turn
500 on debugging in the environment, pass your own filehandle to save
501 debug to, or create your own callback.
502 Why didn't my search run any SQL?
504 DBIx::Class runs the actual SQL statement as late as possible, thus
505 if you create a resultset using "search" in scalar context, no
506 query is executed. You can create further resultset refinements by
507 calling search again or relationship accessors. The SQL query is
508 only run when you ask the resultset for an actual result object.
509 How do I deal with tables that lack a primary key?
511 If your table lacks a primary key, DBIx::Class can't work out which
512 row it should operate on, for example to delete or update.
513 However, a UNIQUE constraint on one or more columns allows
514 DBIx::Class to uniquely identify the row, so you can tell
515 DBIx::Class::ResultSource these columns act as a primary key, even
516 if they don't from the database's point of view:
517 $resultset->set_primary_key(@column);
519 How do I make my program start faster?
521 Look at the tips in "STARTUP SPEED" in
522 DBIx::Class::Manual::Cookbook
523 How do I reduce the overhead of database queries?
525 You can reduce the overhead of object creation within DBIx::Class
526 using the tips in "Skip result object creation for faster results"
527 in DBIx::Class::Manual::Cookbook and "Get raw data for blindingly
528 fast results" in DBIx::Class::Manual::Cookbook
529 How do I override a run time method (e.g. a relationship accessor)?
531 If you need access to the original accessor, then you must "wrap
532 around" the original method. You can do that either with
533 Moose::Manual::MethodModifiers or Class::Method::Modifiers. The
534 code example works for both modules:
535 package Your::Schema::Group;
537 use Class::Method::Modifiers;
538 # ... declare columns ...
540 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
542 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
543 # if the server group is a "super group", then return all servers
545 # otherwise return only servers that belongs to the given group
546 around 'servers' => sub {
547 my $orig = shift;
548 my $self = shift;
549 return $self->$orig(@_) unless $self->is_super_group;
551 return $self->result_source->schema->resultset('Server')->all;
552 };
553 If you just want to override the original method, and don't care
555 about the data from the original accessor, then you have two
556 options. Either use Method::Signatures::Simple that does most of
557 the work for you, or do it the "dirty way".
558 Method::Signatures::Simple way:
560 package Your::Schema::Group;
562 use Method::Signatures::Simple;
563 # ... declare columns ...
565 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
567 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
568 # The method keyword automatically injects the annoying my $self = shift; for you.
570 method servers {
571 return $self->result_source->schema->resultset('Server')->search({ ... });
572 }
573 The dirty way:
575 package Your::Schema::Group;
577 use Sub::Name;
578 # ... declare columns ...
580 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
582 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
583 *servers = subname servers => sub {
585 my $self = shift;
586 return $self->result_source->schema->resultset('Server')->search({ ... });
587 };
588 Notes for CDBI users
590 Is there a way to make an object auto-stringify itself as a particular
591 column or group of columns (a-la cdbi Stringfy column group, or
592 stringify_self method) ?
593 See "Stringification" in DBIx::Class::Manual::Cookbook
594 Troubleshooting
596 Help, I can't connect to postgresql!
597 If you get an error such as:
598 DBI connect('dbname=dbic','user',...) failed: could not connect to server:
600 No such file or directory Is the server running locally and accepting
601 connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
602 Likely you have/had two copies of postgresql installed
604 simultaneously, the second one will use a default port of 5433,
605 while DBD::Pg is compiled with a default port of 5432.
606 You can change the port setting in "postgresql.conf".
608 I've lost or forgotten my mysql password
610 Stop mysqld and restart it with the --skip-grant-tables option.
611 Issue the following statements in the mysql client.
613 UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
615 FLUSH PRIVILEGES;
616 Restart mysql.
618 Taken from:
620 <http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html>.
622
624 Check the list of additional DBIC resources.
625
627 This module is free software copyright by the DBIx::Class (DBIC)
628 authors. You can redistribute it and/or modify it under the same terms
629 as the DBIx::Class library.
630perl v5.34.0 2022-01-21 DBIx::Class::Manual::FAQ(3)