Name

Object::Relation::Meta::Attribute::Schema - Object::Relation database store builder

Synopsis

  # Assuming MyThingy was generated by Object::Relation::Meta and that we're building
  # a data store schema.
  my $class = MyThingy->my_class;

  print "\nAttributes:\n";
  for my $attr ($class->attributes) {
      print "  o ", $attr->name, $/;
      print "    Column: ", $attr->column, $/;
      if (my $idx = $attr->index) {
          print "    Index: $idx\n";
      }
      if (my $ref = $attr->references) {
          print "    References ", $ref->package, $/;
          print "       On Delete: ", $attr->on_delete, $/;
      }
  }

Description

This module is provides metadata for all Object::Relation class attributes while building a storage schema. Loading Object::Relation::Schema causes it to be used instead of Object::Relation::Meta::Attribute. This is so that extra metadata methods are available that are useful in constructing the schema, but are not otherwise useful when an application is actually in use.

Instance Interface

Accessor Methods

on_delete

  my $on_delete = $attr->on_delete;

Returns a string describing what to do with an object that links to another object when that other object is deleted. This is only relevant when the attribute object represents that relationship (that is, when references() returns true). The possible values for this attributes are:

CASCADE
RESTRICT
SET NULL
SET DEFAULT
NO ACTION

The default is "RESTRICT".

column

  my $column = $attr->column;

Returns the name of the database table column for this attribute. The table column name will generally be the same as the attribute name, but for contained objects, in which the column is a foreign key column, the name will be the attribute name plus "_id".

view_column

  my $view_column = $attr->view_column;

Returns the name of the database view column for this attribute. The view column name will generally be the same as the column name, but for attributes that reference other objects, the name will be the class key for the contained object plus "__id". IOW, contained object foreign key columns have a double-underscore in views and a single underscore in tables.

foreign_key

  my $fk = $class->foreign_key;

Attributes that are references to another Object::Relation object will need to have a foreign key constraint. This method returns the name of that constraint, which starts with "fk_", then the key name the current class, then the name of the current attribute, followed by '_id'.

For example, the foreign key for the "contact_type" attribute of the "contact" class is named "fk_contact_contact_type_id" and applies to the "contact" table and references, of course, the "id" column of the "contact_type" table.

If the parent() method returns a false value, this method returns undef.

Instance Methods

index

  my $index = $attr->index;
  $idx = $attr->index($class);

Returns the name of an index for the attribute, if the attribute requires an index. The name of the index is "idx_" plus the class key plus the name of the attribute. Pass in a Object::Relation::Meta::Class object to use its key for the class key part of the name. This is useful for creating indexes for classes that inherit from the class for which the attribute was defined, and prevents duplicately named indexes when more than one class inherits from a class with an attribute requiring an index.

build

This private method overrides the parent build() method in order to gather extra metadata information necessary for building a data store schema.

Copyright and License

Copyright (c) 2004-2006 Kineticode, Inc. <info@obj_relode.com>

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.