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.