NAME

       Alzabo::Create::ForeignKey - Foreign key objects for schema creation.

SYNOPSIS

         use Alzabo::Create::ForeignKey;

DESCRIPTION

       A foreign key is an object defined by several properties.  It represents a relationship
       from a column or columns in one table to a column or columns in another table.

       This relationship is defined by its cardinality (one to one, one to many, or many to one)
       and its dependencies (whether or not table X is dependent on table Y, and vice versa).

       Many to many relationships are not allowed.  However, you may indicate such a relationship
       when using the Alzabo::Create::Schema->add_relation method method, and it will create the
       necessary intermediate linking table for you.

INHERITS FROM

       "Alzabo::ForeignKey"

       Note: all relevant documentation from the superclass has been merged into this document.

METHODS

   new
       The constructor takes the following parameters:

       •   columns_from => "Alzabo::Create::Column" object(s)

       •   columns_to => "Alzabo::Create::Column" object(s)

           These two parameters may be either a single column or a reference to an array columns.
           The number of columns in the two parameters must match.

       •   cardinality => [1, 1], [1, 'n'], or ['n', 1]

       •   from_is_dependent => $boolean

       •   to_is_dependent => $boolean

       •   comment => $comment

           An optional comment.

       It returns a new "Alzabo::Create::ForeignKey" object.

       Throws: "Alzabo::Exception::Params"

   table_from
   table_to
       Returns the relevant "Alzabo::Create::Table" object.

   columns_from
   columns_to
       Returns the relevant "Alzabo::Create::Column" object(s) for the property as an array.

   column_pairs
       Returns an array of array references.  The references are to two column array of
       "Alzabo::Create::Column" objects.  These two columns correspond in the tables being linked
       together.

   set_columns_from ("Alzabo::Create::Column" object(s))
       Sets the column(s) that the relation is from.  This can be either a single column object
       or a reference to an array of column objects.

       Throws: "Alzabo::Exception::Params"

   set_columns_to ("Alzabo::Create::Column" object(s))
       Sets the column(s) that the relation is to.  This can be either a single column object or
       a reference to an array of column objects.

       Throws: "Alzabo::Exception::Params"

   cardinality
       Returns a two element array containing the two portions of the cardinality of the
       relationship.  Each portion will be either '1' or 'n'.

   from_is_dependent
   to_is_dependent
       Returns a boolean value indicating whether there is a dependency from one table to the
       other.

   is_one_to_one
   is_one_to_many
   is_many_to_one
       Returns a boolean value indicating what kind of relationship the object represents.

   set_cardinality (\@cardinality) see above for details
       Sets the cardinality of the foreign key.

       Throws: "Alzabo::Exception::Params"

   set_from_is_dependent ($boolean)
       Indicates whether or not the first table in the foreign key is dependent on the other
       (i.e. whether the 'from' table is dependent on the 'to' table).

   set_to_is_dependent ($boolean)
       Indicates whether or not the second table in the foreign key is dependent on the other
       (i.e. whether the 'to' table is dependent on the 'from' table).

   id
       Returns a string uniquely identifying the foreign key.

   is_same_relationship_as ($fk)
       Given a foreign key object, this returns true if the two objects represent the same
       relationship.  However, the two objects may represent the same relationship from different
       table's points of view.

   comment
       Returns the comment associated with the foreign key object, if any.

   set_comment ($comment)
       Sets the comment for the foreign key object.

AUTHOR

       Dave Rolsky, <autarch@urth.org>