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DBIx::Class::Manual::FAQ(3)          User Contributed Perl Documentation         DBIx::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 selfcontained
           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)