code: def _load_relation(self, models, name, constraints):
          
          relation = self.get_relation(name)
  
          relation.add_eager_constraints(models)
  
          if callable(constraints):
              constraints(relation)
          else:
              relation.merge_query(constraints)
  
          models = relation.init_relation(models, name)
  
          results = relation.get_eager()
  
          return relation.match(models, results, name)
docs: Eagerly load the relationship on a set of models.
  
          :rtype: list