Clarification cascade_* attribute defaults documentation

[dbsrgits/DBIx-Class-Historic.git] / lib / DBIx / Class / Manual / Component.pod

=head1 NAME

DBIx::Class::Manual::Component - Developing DBIx::Class Components

=head1 WHAT IS A COMPONENT

A component is a module that can be added in to your DBIx::Class
classes to provide extra functionality. A good example is the PK::Auto
component which automatically retrieves primary keys that the database
itself creates, after the insert has happened.

=head1 USING

Components are loaded using the load_components() method within your
DBIx::Class classes.

  package My::Thing;
  use base qw( DBIx::Class::Core );
  __PACKAGE__->load_components(qw/InflateColumn::DateTime TimeStamp/);

Generally you do not want to specify the full package name
of a component, instead take off the DBIx::Class:: part of
it and just include the rest.  If you do want to load a
component outside of the normal namespace you can do so
by prepending the component name with a +.

  __PACKAGE__->load_components(qw/ +My::Component /);

Once a component is loaded all of it's methods, or otherwise,
that it provides will be available in your class.

The order in which is you load the components may be very
important, depending on the component. If you are not sure,
then read the docs for the components you are using and see
if they mention anything about the order in which you should
load them.

=head1 CREATING COMPONENTS

Making your own component is very easy.

  package DBIx::Class::MyComp;
  use base qw(DBIx::Class);
  # Create methods, accessors, load other components, etc.
  1;

When a component is loaded it is included in the calling
class' inheritance chain using L<Class::C3>.  As well as
providing custom utility methods, a component may also
override methods provided by other core components, like
L<DBIx::Class::Row> and others.  For example, you
could override the insert and delete methods.

  sub insert {
    my $self = shift;
    # Do stuff with $self, like set default values.
    return $self->next::method( @_ );
  }
  
  sub delete {
    my $self = shift;
    # Do stuff with $self.
    return $self->next::method( @_ );
  }

Now, the order that a component is loaded is very important.  Components 
that are loaded first are the first ones in the inheritance stack.  So, if 
you override insert() but the DBIx::Class::Row component is loaded first 
then your insert() will never be called, since the DBIx::Class::Row insert() 
will be called first.  If you are unsure as to why a given method is not 
being called try printing out the Class::C3 inheritance stack.

  print join ', ' => Class::C3::calculateMRO('YourClass::Name');

Check out the L<Class::C3> docs for more information about inheritance.

=head1 EXISTING COMPONENTS

=head2 Extra

These components provide extra functionality beyond 
basic functionality that you can't live without.

L<DBIx::Class::Serialize::Storable> - Hooks for Storable freeze/thaw.

L<DBIx::Class::CDBICompat> - Class::DBI Compatibility layer.

L<DBIx::Class::FormTools> - Build forms with multiple interconnected objects.

L<DBIx::Class::HTMLWidget> - Like FromForm but with DBIx::Class and HTML::Widget.

L<DBIx::Class::Ordered> - Modify the position of objects in an ordered list.

L<DBIx::Class::PK::Auto> - Retrieve automatically created primary keys upon insert.

L<DBIx::Class::QueriesTime> - Display the amount of time it takes to run queries.

L<DBIx::Class::RandomStringColumns> - Declare virtual columns that return random strings.

L<DBIx::Class::UTF8Columns> - Force UTF8 (Unicode) flag on columns.

L<DBIx::Class::UUIDColumns> - Implicit UUID columns.

L<DBIx::Class::WebForm> - CRUD methods.

=head2 Experimental

These components are under development, their interfaces may
change, they may not work, etc.  So, use them if you want, but
be warned.

L<DBIx::Class::Validation> - Validate all data before submitting to your database.

=head2 Core

These are the components that all, or nearly all, people will use
without even knowing it.  These components provide most of
DBIx::Class' functionality.

L<DBIx::Class::Core> - Loads various components that "most people" would want.

L<DBIx::Class::AccessorGroup> - Lets you build groups of accessors.

L<DBIx::Class::DB> - Non-recommended classdata schema component.

L<DBIx::Class::InflateColumn> - Automatically create objects from column data.

L<DBIx::Class::PK> - This class contains methods for handling primary keys and methods depending on them.

L<DBIx::Class::Relationship> - Inter-table relationships.

L<DBIx::Class::ResultSourceProxy::Table> - Provides a classdata table object and method proxies.

L<DBIx::Class::Row> - Basic row methods.

=head1 SEE ALSO

L<DBIx::Class::Manual::Cookbook>

=head1 AUTHOR

Aran Clary Deltac <bluefeet@cpan.org>