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NAME
       DBIx::Class::Manual::FAQ - Frequently Asked Questions (in theory)

DESCRIPTION
       This document is intended as an anti-map of the documentation. If you
       know what you want to do, but not how to do it in DBIx::Class, then
       look here. It does not contain much code or examples, it just gives
       explanations and pointers to the correct pieces of documentation to
       read.

FAQs
       How Do I:

   Getting started
       .. create a database to use?
	   First, choose a database. For testing/experimenting, we recommend
	   DBD::SQLite, which is a self-contained small database (i.e. all you
	   need to do is to install DBD::SQLite from CPAN, and it works).

	   Next, spend some time defining which data you need to store, and
	   how it relates to the other data you have. For some help on
	   normalisation, go to <http://b62.tripod.com/doc/dbbase.htm>.

	   Now, decide whether you want to have the database itself be the
	   definitive source of information about the data layout, or your
	   DBIx::Class schema. If it's the former, look up the documentation
	   for your database, eg. <http://sqlite.org/lang_createtable.html>,
	   on how to create tables, and start creating them. For a nice
	   universal interface to your database, you can try DBI::Shell. If
	   you decided on the latter choice, read the FAQ on setting up your
	   classes manually, and the one on creating tables from your schema.

       .. use DBIx::Class with Catalyst?
	   Install Catalyst::Model::DBIC::Schema from CPAN. See its
	   documentation, or below, for further details.

       .. set up my DBIx::Class classes automatically from my database?
	   Install DBIx::Class::Schema::Loader from CPAN, and read its
	   documentation.

       .. set up my DBIx::Class classes manually?
	   Look at the DBIx::Class::Manual::Example and come back here if you
	   get lost.

       .. create my database tables from my DBIx::Class schema?
	   Create your classes manually, as above. Write a script that calls
	   "deploy" in DBIx::Class::Schema. See there for details, or the
	   DBIx::Class::Manual::Cookbook.

       .. store/retrieve Unicode data in my database?
	   Make sure you database supports Unicode and set the connect
	   attributes appropriately - see "Using Unicode" in
	   DBIx::Class::Manual::Cookbook

       .. connect to my database?
	   Once you have created all the appropriate table/source classes, and
	   an overall Schema class, you can start using them in an
	   application. To do this, you need to create a central Schema
	   object, which is used to access all the data in the various tables.
	   See "connect" in DBIx::Class::Schema for details. The actual
	   connection does not happen until you actually request data, so
	   don't be alarmed if the error from incorrect connection details
	   happens a lot later.

       .. use DBIx::Class across multiple databases?
	   If your database server allows you to run querys across multiple
	   databases at once, then so can DBIx::Class. All you need to do is
	   make sure you write the database name as part of the "table" in
	   DBIx::Class::ResultSource call. Eg:

	     __PACKAGE__->table('mydb.mytablename');

	   And load all the Result classes for both / all databases using one
	   "load_namespaces" in DBIx::Class::Schema call.

       .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
	   Add the name of the schema to the "table" in
	   DBIx::Class::ResultSource as part of the name, and make sure you
	   give the one user you are going to connect with has permissions to
	   read/write all the schemas/tables as necessary.

   Relationships
       .. tell DBIx::Class about relationships between my tables?
	   There are a variety of relationship types that come pre-defined for
	   you to use.	These are all listed in DBIx::Class::Relationship. If
	   you need a non-standard type, or more information, look in
	   DBIx::Class::Relationship::Base.

       .. define a one-to-many relationship?
	   This is called a "has_many" relationship on the one side, and a
	   "belongs_to" relationship on the many side. Currently these need to
	   be set up individually on each side. See DBIx::Class::Relationship
	   for details.

       .. define a relationship where this table contains another table's
       primary key? (foreign key)
	   Create a "belongs_to" relationship for the field containing the
	   foreign key.	 See "belongs_to" in DBIx::Class::Relationship.

       .. define a foreign key relationship where the key field may contain
       NULL?
	   Just create a "belongs_to" relationship, as above. If the column is
	   NULL then the inflation to the foreign object will not happen. This
	   has a side effect of not always fetching all the relevant data, if
	   you use a nullable foreign-key relationship in a JOIN, then you
	   probably want to set the "join_type" to "left".

       .. define a relationship where the key consists of more than one
       column?
	   Instead of supplying a single column name, all relationship types
	   also allow you to supply a hashref containing the condition across
	   which the tables are to be joined. The condition may contain as
	   many fields as you like. See DBIx::Class::Relationship::Base.

       .. define a relationship bridge across an intermediate table? (many-to-
       many)
	   The term 'relationship' is used loosely with many_to_many as it is
	   not considered a relationship in the fullest sense.	For more info,
	   read the documentation on "many_to_many" in
	   DBIx::Class::Relationship.

       .. stop DBIx::Class from attempting to cascade deletes on my has_many
       and might_have relationships?
	   By default, DBIx::Class cascades deletes and updates across
	   "has_many" and "might_have" relationships. You can disable this
	   behaviour on a per-relationship basis by supplying "cascade_delete
	   => 0" in the relationship attributes.

	   The cascaded operations are performed after the requested delete or
	   update, so if your database has a constraint on the relationship,
	   it will have deleted/updated the related records or raised an
	   exception before DBIx::Class gets to perform the cascaded
	   operation.

	   See DBIx::Class::Relationship.

       .. use a relationship?
	   Use its name. An accessor is created using the name. See examples
	   in "Using relationships" in DBIx::Class::Manual::Cookbook.

   Searching
       .. search for data?
	   Create a $schema object, as mentioned above in ".. connect to my
	   database?". Find the ResultSet that you want to search in, by
	   calling "$schema->resultset('MySource')" and call "search" on it.
	   See "search" in DBIx::Class::ResultSet.

       .. search using database functions?
	   Supplying something like:

	    ->search({'mydatefield' => 'now()'})

	   to search, will probably not do what you expect. It will quote the
	   text "now()", instead of trying to call the function. To provide
	   literal, unquoted text you need to pass in a scalar reference, like
	   so:

	    ->search({'mydatefield' => \'now()'})

       .. sort the results of my search?
	   Supply a list of columns you want to sort by to the "order_by"
	   attribute. See "order_by" in DBIx::Class::ResultSet.

       .. sort my results based on fields I've aliased using "as"?
	   You didn't alias anything, since as has nothing to do with the
	   produced SQL. See "select" in DBIx::Class::ResultSet for details.

       .. group the results of my search?
	   Supply a list of columns you want to group on, to the "group_by"
	   attribute, see "group_by" in DBIx::Class::ResultSet.

       .. group my results based on fields I've aliased using "as"?
	   You don't. See the explanation on ordering by an alias above.

       .. filter the results of my search?
	   The first argument to "search" is a hashref of accessor names and
	   values to filter them by, for example:

	    ->search({'created_time' => { '>=', '2006-06-01 00:00:00' } })

	   Note that to use a function here you need to make it a scalar
	   reference:

	    ->search({'created_time' => { '>=', \'yesterday()' } })

       .. search in several tables simultaneously?
	   To search in two related tables, you first need to set up
	   appropriate relationships between their respective classes. When
	   searching you then supply the name of the relationship to the
	   "join" attribute in your search, for example when searching in the
	   Books table for all the books by the author "Fred Bloggs":

	    ->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors' })

	   The type of join created in your SQL depends on the type of
	   relationship between the two tables, see DBIx::Class::Relationship
	   for the join used by each relationship.

       .. create joins with conditions other than column equality?
	   Currently, DBIx::Class can only create join conditions using
	   equality, so you're probably better off creating a "view" in your
	   database, and using that as your source. A "view" is a stored SQL
	   query, which can be accessed similarly to a table, see your
	   database documentation for details.

       .. search with an SQL function on the left hand side?
	   To use an SQL function on the left hand side of a comparison you
	   currently need to resort to literal SQL:

	    ->search( \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ] );

	   Note: the "plain_value" string in the "[ plain_value => 1979 ]"
	   part should be either the same as the name of the column (do this
	   if the type of the return value of the function is the same as the
	   type of the column) or in the case of a function it's currently
	   treated as a dummy string (it is a good idea to use "plain_value"
	   or something similar to convey intent). The value is currently only
	   significant when handling special column types (BLOBs, arrays,
	   etc.), but this may change in the future.

       .. find more help on constructing searches?
	   Behind the scenes, DBIx::Class uses SQL::Abstract to help construct
	   its SQL searches. So if you fail to find help in the
	   DBIx::Class::Manual::Cookbook, try looking in the SQL::Abstract
	   documentation.

       .. make searches in Oracle (10gR2 and newer) case-insensitive?
	   To make Oracle behave like most RDBMS use on_connect_do to issue
	   alter session statements on database connection establishment:

	    ->on_connect_do("ALTER SESSION SET NLS_COMP = 'LINGUISTIC'");
	    ->on_connect_do("ALTER SESSION SET NLS_SORT = '<NLS>_CI'");
	    e.g.
	    ->on_connect_do("ALTER SESSION SET NLS_SORT = 'BINARY_CI'");
	    ->on_connect_do("ALTER SESSION SET NLS_SORT = 'GERMAN_CI'");

   Fetching data
       .. fetch as much data as possible in as few select calls as possible?
	   See the prefetch examples in the Cookbook.

       .. fetch a whole column of data instead of a row?
	   Call "get_column" on a DBIx::Class::ResultSet. This returns a
	   DBIx::Class::ResultSetColumn. See its documentation and the
	   Cookbook for details.

       .. fetch a formatted column?
	   In your table schema class, create a "private" column accessor
	   with:

	     __PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });

	   Then, in the same class, implement a subroutine called "my_column"
	   that fetches the real value and does the formatting you want.

	   See the Cookbook for more details.

       .. fetch a single (or topmost) row?
	   Use the "rows" in DBIx::Class::ResultSet and "order_by" in
	   DBIx::Class::ResultSet attributes to order your data and pick off a
	   single row.

	   See also "Retrieve_one_and_only_one_row_from_a_resultset" in
	   DBIx::Class::Manual::Cookbook.

	   A less readable way is to ask a regular search to return 1 row,
	   using "slice" in DBIx::Class::ResultSet:

	     ->search->(undef, { order_by => "id DESC" })->slice(0)

	   which (if supported by the database) will use LIMIT/OFFSET to hint
	   to the database that we really only need one row. This can result
	   in a significant speed improvement. The method using "single" in
	   DBIx::Class::ResultSet mentioned in the cookbook can do the same if
	   you pass a "rows" attribute to the search.

       .. refresh a row from storage?
	   Use "discard_changes" in DBIx::Class::Row.

	     $row->discard_changes

	   Discarding changes and refreshing from storage are two sides fo the
	   same coin.  When you want to discard your local changes, just re-
	   fetch the row from storage.	When you want to get a new, fresh copy
	   of the row, just re-fetch the row from storage.  "discard_changes"
	   in DBIx::Class::Row does just that by re-fetching the row from
	   storage using the row's primary key.

       .. fetch my data a "page" at a time?
	   Pass the "rows" and "page" attributes to your search, eg:

	     ->search({}, { rows => 10, page => 1});

       .. get a count of all rows even when paging?
	   Call "pager" on the paged resultset, it will return a Data::Page
	   object. Calling "total_entries" on the pager will return the
	   correct total.

	   "count" on the resultset will only return the total number in the
	   page.

   Inserting and updating data
       .. insert a row with an auto incrementing primary key?
	   This happens automatically. After creating a row object, the
	   primary key value created by your database can be fetched by
	   calling "id" (or the access of your primary key column) on the
	   object.

       .. insert a row with a primary key that uses a sequence?
	   You need to create a trigger in your database that updates your
	   primary key field from the sequence. To help PK::Auto find the next
	   key value, you can tell it the name of the sequence in the
	   "column_info" supplied with "add_columns".

	    ->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });

       .. insert many rows of data efficiently?
	   The "populate" method in DBIx::Class::ResultSet provides efficient
	   bulk inserts.

	   DBIx::Class::Fixtures provides an alternative way to do this.

       .. update a collection of rows at the same time?
	   Create a resultset using a "search", to filter the rows of data you
	   would like to update, then call "update" on the resultset to change
	   all the rows at once.

       .. use database functions when updating rows?
       .. update a column using data from another column?
	   To stop the column name from being quoted, you'll need to tell DBIC
	   that the right hand side is an SQL identifier (it will be quoted
	   properly if you have quoting enabled):

	    ->update({ somecolumn => { -ident => 'othercolumn' } })

	   This method will not retrieve the new value and put it in your Row
	   object. To fetch the new value, use the "discard_changes" method on
	   the Row.

	     # will return the scalar reference:
	     $row->somecolumn()

	     # issue a select using the PK to re-fetch the row data:
	     $row->discard_changes();

	     # Now returns the correct new value:
	     $row->somecolumn()

	   To update and refresh at once, chain your calls:

	     $row->update({ 'somecolumn' => { -ident => 'othercolumn' } })->discard_changes;

       .. store JSON/YAML in a column and have it deflate/inflate
       automatically?
	   You can use DBIx::Class::InflateColumn to accomplish YAML/JSON
	   storage transparently.

	   If you want to use JSON, then in your table schema class, do the
	   following:

	    use JSON;

	    __PACKAGE__->add_columns(qw/ ... my_column ../)
	    __PACKAGE__->inflate_column('my_column', {
		inflate => sub { jsonToObj(shift) },
		deflate => sub { objToJson(shift) },
	    });

	   For YAML, in your table schema class, do the following:

	    use YAML;

	    __PACKAGE__->add_columns(qw/ ... my_column ../)
	    __PACKAGE__->inflate_column('my_column', {
		inflate => sub { YAML::Load(shift) },
		deflate => sub { YAML::Dump(shift) },
	    });

	   This technique is an easy way to store supplemental unstructured
	   data in a table. Be careful not to overuse this capability,
	   however. If you find yourself depending more and more on some data
	   within the inflated column, then it may be time to factor that data
	   out.

   Custom methods in Result classes
       You can add custom methods that do arbitrary things, even to unrelated
       tables.	For example, to provide a "$book->foo()" method which searches
       the cd table, you'd could add this to Book.pm:

	 sub foo {
	   my ($self, $col_data) = @_;
	   return $self->result_source->schema->resultset('cd')->search($col_data);
	 }

       And invoke that on any Book Result object like so:

	 my $rs = $book->foo({ title => 'Down to Earth' });

       When two tables ARE related, DBIx::Class::Relationship::Base provides
       many methods to find or create data in related tables for you. But if
       you want to write your own methods, you can.

       For example, to provide a "$book->foo()" method to manually implement
       what create_related() from DBIx::Class::Relationship::Base does, you
       could add this to Book.pm:

	 sub foo {
	   my ($self, $relname, $col_data) = @_;
	   return $self->related_resultset($relname)->create($col_data);
	 }

       Invoked like this:

	 my $author = $book->foo('author', { name => 'Fred' });

   Misc
       How do I store my own (non-db) data in my DBIx::Class objects?
	   You can add your own data accessors to your Result classes.

	   One method is to use the built in mk_group_accessors (via
	   Class::Accessor::Grouped)

		   package App::Schema::Result::MyTable;

		   use parent 'DBIx::Class::Core';

		   __PACKAGE__->table('foo'); #etc
		   __PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group

	   An another method is to use Moose with your DBIx::Class package.

		   package App::Schema::Result::MyTable;

		   use Moose; # import Moose
		   use Moose::Util::TypeConstraint; # import Moose accessor type constraints

		   extends 'DBIx::Class::Core'; # Moose changes the way we define our parent (base) package

		   has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute

		   __PACKAGE__->table('foo'); # etc

	   With either of these methods the resulting use of the accesssor
	   would be

		   my $row;

		   # assume that somewhere in here $row will get assigned to a MyTable row

		   $row->non_column_data('some string'); # would set the non_column_data accessor

		   # some other stuff happens here

		   $row->update(); # would not inline the non_column_data accessor into the update

       How do I use DBIx::Class objects in my TT templates?
	   Like normal objects, mostly. However you need to watch out for TT
	   calling methods in list context. When calling relationship
	   accessors you will not get resultsets, but a list of all the
	   related objects.

	   Use the "search_rs" in DBIx::Class::ResultSet method, or the
	   relationship accessor methods ending with "_rs" to work around this
	   issue.

	   See also "has_many" in DBIx::Class::Relationship.

       See the SQL statements my code is producing?
	   Set the shell environment variable "DBIC_TRACE" to a true value.

	   For more info see DBIx::Class::Storage for details of how to turn
	   on debugging in the environment, pass your own filehandle to save
	   debug to, or create your own callback.

       Why didn't my search run any SQL?
	   DBIx::Class runs the actual SQL statement as late as possible, thus
	   if you create a resultset using "search" in scalar context, no
	   query is executed. You can create further resultset refinements by
	   calling search again or relationship accessors. The SQL query is
	   only run when you ask the resultset for an actual row object.

       How do I deal with tables that lack a primary key?
	   If your table lacks a primary key, DBIx::Class can't work out which
	   row it should operate on, for example to delete or update.
	   However, a UNIQUE constraint on one or more columns allows
	   DBIx::Class to uniquely identify the row, so you can tell
	   DBIx::Class::ResultSource these columns act as a primary key, even
	   if they don't from the database's point of view:

	    $resultset->set_primary_key(@column);

       How do I make my program start faster?
	   Look at the tips in "STARTUP SPEED" in
	   DBIx::Class::Manual::Cookbook

       How do I reduce the overhead of database queries?
	   You can reduce the overhead of object creation within DBIx::Class
	   using the tips in "Skip row object creation for faster results" in
	   DBIx::Class::Manual::Cookbook and "Get raw data for blindingly fast
	   results" in DBIx::Class::Manual::Cookbook

       How do I override a run time method (e.g. a relationship accessor)?
	   If you need access to the original accessor, then you must "wrap
	   around" the original method.	 You can do that either with
	   Moose::Manual::MethodModifiers or Class::Method::Modifiers.	The
	   code example works for both modules:

	       package Your::Schema::Group;
	       use Class::Method::Modifiers;

	       # ... declare columns ...

	       __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
	       __PACKAGE__->many_to_many('servers', 'group_servers', 'server');

	       # if the server group is a "super group", then return all servers
	       # otherwise return only servers that belongs to the given group
	       around 'servers' => sub {
		   my $orig = shift;
		   my $self = shift;

		   return $self->$orig(@_) unless $self->is_super_group;
		   return $self->result_source->schema->resultset('Server')->all;
	       };

	   If you just want to override the original method, and don't care
	   about the data from the original accessor, then you have two
	   options. Either use Method::Signatures::Simple that does most of
	   the work for you, or do it the "dirty way".

	   Method::Signatures::Simple way:

	       package Your::Schema::Group;
	       use Method::Signatures::Simple;

	       # ... declare columns ...

	       __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
	       __PACKAGE__->many_to_many('servers', 'group_servers', 'server');

	       # The method keyword automatically injects the annoying my $self = shift; for you.
	       method servers {
		   return $self->result_source->schema->resultset('Server')->search({ ... });
	       }

	   The dirty way:

	       package Your::Schema::Group;
	       use Sub::Name;

	       # ... declare columns ...

	       __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
	       __PACKAGE__->many_to_many('servers', 'group_servers', 'server');

	       *servers = subname servers => sub {
		   my $self = shift;
		   return $self->result_source->schema->resultset('Server')->search({ ... });
	       };

   Notes for CDBI users
       Is there a way to make an object auto-stringify itself as a particular
       column or group of columns (a-la cdbi Stringfy column group, or
       stringify_self method) ?
	   See "Stringification" in DBIx::Class::Manual::Cookbook

   Troubleshooting
       Help, I can't connect to postgresql!
	   If you get an error such as:

	     DBI connect('dbname=dbic','user',...) failed: could not connect to server:
	     No such file or directory Is the server running locally and accepting
	     connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

	   Likely you have/had two copies of postgresql installed
	   simultaneously, the second one will use a default port of 5433,
	   while DBD::Pg is compiled with a default port of 5432.

	   You can change the port setting in "postgresql.conf".

       I've lost or forgotten my mysql password
	   Stop mysqld and restart it with the --skip-grant-tables option.

	   Issue the following statements in the mysql client.

	     UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
	     FLUSH PRIVILEGES;

	   Restart mysql.

	   Taken from:

	   http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html
	   <http://dev.mysql.com/doc/refman/5.1/en/resetting-
	   permissions.html>.

perl v5.12.5			  2011-07-26	   DBIx::Class::Manual::FAQ(3)
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