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DBIx::Class::Manual::FUser)Contributed Perl DocumenDBIx::Class::Manual::FAQ(3)

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 queries 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 call.
	   Eg:

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

	   And load all	the Result classes for both / all databases by calling
	   "load_namespaces" in	DBIx::Class::Schema.

       .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
	   Add the name	of the schema to the table name, when invoking table,
	   and make sure the user you are about	to connect as 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) =	?', 1979 ] );

       .. find more help on constructing searches?
	   Behind the scenes, DBIx::Class uses SQL::Abstract::Classic 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::Classic 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'");

       .. format a DateTime object for searching?
	   search and find do not take DBIx::Class::InflateColumn into
	   account, and	so your	DateTime object	will not be correctly deflated
	   into	a format your RDBMS expects.

	   The datetime_parser method on your storage object can be used to
	   return the object that would	normally do this, so it's easy to do
	   it manually:

	     my	$dtf = $schema->storage->datetime_parser;
	     my	$rs = $schema->resultset('users')->search(
	       {
		 signup_date =>	{
		   -between => [
		     $dtf->format_datetime($dt_start),
		     $dtf->format_datetime($dt_end),
		   ],
		 }
	       },
	     );

	   With	in a Result Class method, you can get this from	the
	   "result_source".

	     my	$dtf = $self->result_source->storage->datetime_parser;

	   This	kludge is necessary only for conditions	passed to search and
	   "find" in DBIx::Class::ResultSet, whereas create and	"update" in
	   DBIx::Class::Row (but not "update" in DBIx::Class::ResultSet) are
	   DBIx::Class::InflateColumn-aware and	will do	the right thing	when
	   supplied an inflated	DateTime object.

   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.

	     $result->discard_changes

	   Discarding changes and refreshing from storage are two sides	of 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 pager object
	    with an API/behavior identical to that of Data::Page from late
	   2009	through	late 2019
	    <https://metacpan.org/pod/release/LBROCARD/Data-
	   Page-2.02/lib/Data/Page.pm>.	 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	result 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:
	     $result->somecolumn()

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

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

	   To update and refresh at once, chain	your calls:

	     $result->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, $rel_name, $col_data) = @_;
	   return $self->related_resultset($rel_name)->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

	   And 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 accessor
	   would be

		   my $result;

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

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

		   # some other	stuff happens here

		   $result->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 result 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 result 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>.

FURTHER	QUESTIONS?
       Check the list of additional DBIC resources.

COPYRIGHT AND LICENSE
       This module is free software copyright by the DBIx::Class (DBIC)
       authors.	You can	redistribute it	and/or modify it under the same	terms
       as the DBIx::Class library.

perl v5.32.1			  2020-03-29	   DBIx::Class::Manual::FAQ(3)

NAME | DESCRIPTION | FAQs | FURTHER QUESTIONS? | COPYRIGHT AND LICENSE

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