internal static DeleteEFElementCommand GetDeleteCommand(
     EntityType conceptualEntityType, Function function, ModificationFunctionType type)
 {
     var cmd = new DeleteFunctionMappingCommand(conceptualEntityType, function, type);
     if (cmd == null)
     {
         // shouldn't happen, just to be safe
         throw new InvalidOperationException();
     }
     return cmd;
 }
 internal override DeleteEFElementCommand GetDeleteCommand()
 {
     var cmd = new DeleteFunctionMappingCommand(this);
     if (cmd == null)
     {
         // shouldn't happen, just to be safe
         throw new InvalidOperationException();
     }
     return cmd;
 }