派生类如何使用基类的映射方法？

Question

想象一下我在 python 中有以下内容（实际语言并不重要，因为我在其他语言（如 php）中也遇到了问题。基类“CarModel”和来自“CarModel”的派生类“TruckModel”。

class CarModel:
    def __init__(self):
        self.__wheel_count: int = 0

    def set_wheel_count(self, value: int) -> None:
        self.__wheel_count = value

class TruckModel(CarModel):
    def __init__(self):
        super().__init__()
        self.__load_in_kg: int = 0

    def set_load_in_kg(self, value: int) -> None:
        self.__load_in_kg= value

如果我现在有一个映射类，它应该转换为例如我的模型的字典，如何为我的派生类重用映射方法？ 特别是如果我有一个包含很多 setter 方法的基类，我必须重复代码，这是我不喜欢的（“干”）。

class VehicleMapper:
    def map_car_dict_to_car_model(dict: Dict) -> CarModel:
        model: CarModel = CarModel()
        model.set_wheel_count(dict['wheelCount'])
        return model

    def map_truck_dict_to_truck_model(dict: Dict) -> TruckModel:
        model: TruckModel= TruckModel()
        model.set_load_in_kg(dict['loadInKg'])
 
        model.set_wheel_count(dict['wheelCount']) #  ??? How can I re-use the map-method for the base class here ???
        
        return model

我可以将映射方法移至模型类，这样就可以了。但我被告知，模型类应该只“保存”数据，而不应该做任何事情。这就是为什么有映射器类，对吗？

Answer 1

更干净、更可靠的方法是使用单独的映射器/工厂。而且更合理，因为在您的情况下，您还需要从字典键到相应模型属性名称的可配置映射。
考虑以下模式：

class CarModel:
    def __init__(self):
        self.__wheel_count: int = 0

    def wheel_count(self, value: int) -> None:
        self.__wheel_count = value

    wheel_count = property(None, wheel_count)

class TruckModel(CarModel):
    def __init__(self):
        super().__init__()
        self.__load_in_kg: int = 0

    def load_in_kg(self, value: int) -> None:
        self.__load_in_kg= value

    load_in_kg = property(None, load_in_kg)


class VehicleFactory:
    """Vehicle base factory"""
    __model__ = None
    __map_keys__ = None

    @classmethod
    def create(cls, data):
        model = cls.__model__()
        for k, attr in cls.__map_keys__.items():
            setattr(model, attr, data[k])
        return model

class CarFactory(VehicleFactory):
    __model__ = CarModel
    __map_keys__ = {'wheelCount': 'wheel_count'}

class TruckFactory(VehicleFactory):
    __model__ = TruckModel
    __map_keys__ = {'wheelCount': 'wheel_count',
                    'loadInKg': 'load_in_kg'}

用途：

---

car = CarFactory.create({'wheelCount': 4})
print(vars(car))    # {'_CarModel__wheel_count': 4}

truck = TruckFactory.create({'wheelCount': 4, 'loadInKg': 500})
print(vars(truck))  # {'_CarModel__wheel_count': 4, '_TruckModel__load_in_kg': 500}

Answer 2

class CarModel:
    mapping = {}

    @staticmethod
    def _key(key, mapping=mapping):
        def decorator(func):
            mapping[key] = func
        return decorator

    @classmethod
    def from_dict(cls, d: dict):
        instance = cls()
        for key, value in d.items():
            cls.mapping[key](instance, value)
        return instance

    def __init__(self):
        self.__wheel_count: int = 0

    @_key('wheelCount')
    def set_wheel_count(self, value: int) -> None:
        self.__wheel_count = value

class TruckModel(CarModel):
    def __init__(self):
        super().__init__()
        self.__load_in_kg: int = 0

    @CarModel._key('loadInKg')
    def set_load_in_kg(self, value: int) -> None:
        self.__load_in_kg= value

这样：

print(vars(CarModel.from_dict({'wheelCount': 4})))
print(vars(TruckModel.from_dict({'wheelCount': 6, 'loadInKg': 8000})))

输出：

{'_CarModel__wheel_count': 4}
{'_CarModel__wheel_count': 6, '_TruckModel__load_in_kg': 8000}

演示：

https://ideone.com/xp2IAB