Tangram::Type::Set::FromOne - map Set::Object using a foreign key

   use Tangram;

   # or
   use Tangram::Core;
   use Tangram::Type::Set::FromOne;

   $schema = Tangram::Schema->new(

      classes => { Basket => { fields => {

      iset =>
      {
         # long form
         fruits =>
         {
            class => 'Fruit',
            coll => 'basket',
         },

         # or (short form)
         fruits => 'Fruit',
      }

This class maps references to Set::Object collections in an intrusive fashion. The persistent fields are grouped in a hash under the iset key in the field hash.

The set may contain only objects of persistent classes. These classes must have a common persistent base class.

Tangram uses a column on the element's table to store the id of the object containing the collection.

CAUTION: the same object may not be an element of the same collection, in two different objects. This mapping may be used only for one-to-many relationships.

The field names are passed in a hash that associates a field name with a field descriptor. The field descriptor may be either a hash or a string. The hash uses the following fields:

* class

Mandatory field class specifies the class of the elements.

* aggreg

Optional field aggreg specifies that the elements of the collection must be removed (erased) from persistent storage along with the containing object. The default is not to aggregate.

* back

Optional field back sets the name of a field that is inserted in the elements. That field acts as a demand-loaded, read-only reference to the object containing the collection.

* coll

Optional field coll sets the name the column containing the id of the containing object. This defaults to 'C_m', where 'C' is the class of the containing object (after passing through the normalisation function), and 'm' is the field name.

* deep_update

Optional field deep_update specificies that all elements have to be updated automatically when update is called on the collection object. Automatic update ensures consisitency between the Perl representation and the DBMS state, but degrades update performance so use it with caution. The default is not to do automatic updates.

If the descriptor is a string, it is interpreted as the name of the element's class. This is equivalent to specifying only the class field in the hash variant.