DBFieldDef :: get_del_empty - DELETE_EMPTY option

The option can be set for references or relationships in order to prevent instances from deletion, which do have references to other object instances. When this option is set for a reference or relationship of an instance, the instance can be deleted only, when the referenced collection is empty. When the option is set for more than one collection, all marked collections must be empty before the instance can be deleted.

When the option is set for an attribute, instances can be deleted only, when all attribute marked this way contain an empty vale