code: def add_constraints(self):
          
          parent_table = self._parent.get_table()
  
          self._set_join()
  
          if self._constraints:
              self._query.where('%s.%s' % (parent_table, self._first_key), '=', self._far_parent.get_key())
docs: Set the base constraints on the relation query.
  
          :rtype: None