NAME

       Tangram::Type::Set::FromMany - maps Set::Object using a link table

SYNOPSIS

          use Tangram;

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

          $schema = Tangram::Schema->new(

             classes => { Company => { fields => {

             set =>
             {
                # long form
                employee =>
                {
                   class => 'Person',
                   table => 'Company_employees',
                   coll => 'company',
                   item => 'employee',
                },

                # short form
                assets => 'Asset',
             }

DESCRIPTION

       Maps a reference to a Set::Object. The persistent fields are grouped in a hash under the
       "set" 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 link table to save the state of the collection. The table has two columns:
       one contains the id of the container objects; the other contains the ids of the elements.

       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

       •   aggreg

       •   table

       •   coll

       •   item

       •   deep_update

       Mandatory field "class" specifies the class of the elements.

       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.

       Optional field "table" sets the name of the link table. This defaults to 'C_F', where C is
       the class of the containing object and F is the field name.

       Optional field "coll" sets the name the column containing the ids of the containing
       objects. This defaults to 'coll'.

       Optional field "item" sets the name the column containing the ids of the elements. This
       defaults to 'item'.

       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.