如何组合我的 Django 模型，以免重复自己？答案

【问题标题】：How do I combine my Django models so that I am not repeating myself?如何组合我的 Django 模型，以免重复自己？
【发布时间】：2021-03-16 15:48:08
【问题描述】：

我意识到我现在使用的 3 个模型有大量共享字段。我想知道浓缩这些模型的最佳方法是什么。我已经阅读了一些关于元类和模型继承的文章，但想看看这样做的“最佳”方法是什么。

models.py

class Car(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    year = models.IntegerField(default=2021, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    seats = models.PositiveSmallIntegerField()
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)


class Truck(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    year = models.IntegerField(default=datetime.now().year, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    seats = models.PositiveSmallIntegerField()
    bed_length = models.CharField(max_length=100)
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)


class Boat(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    year = models.PositiveSmallIntegerField(default=datetime.now().year, validators=[MaxValueValidator(datetime.now().year)])
    length = models.CharField(max_length=100)
    width = models.CharField(max_length=100)
    HIN = models.CharField(max_length=14, validators=[MinLengthValidator(12)], blank=True)
    current_hours = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)

【问题讨论】：

标签： django django-models django-rest-framework dry

【解决方案1】：

我可以注意到有些字段相似但不一样，例如year 并不相同。因此，我向您提出以下建议。

class TimeStampedModel(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    modified = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True


class Vehicule(TimeStampedModel):
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)

    class Meta:
        abstract = True


class WheeledVehicle(Vehicule):
    seats = models.PositiveSmallIntegerField()
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()

    class Meta:
        abstract = True


class Car(WheeledVehicle):
    year = models.IntegerField(default=2021, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    
    
class Truck(WheeledVehicle):
    year = models.IntegerField(default=datetime.now().year, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    bed_length = models.CharField(max_length=100)
    

class Boat(Vehicule):
    year = models.PositiveSmallIntegerField(default=datetime.now().year, validators=[MaxValueValidator(datetime.now().year)])
    length = models.CharField(max_length=100)
    width = models.CharField(max_length=100)
    HIN = models.CharField(max_length=14, validators=[MinLengthValidator(12)], blank=True)
    current_hours = models.PositiveSmallIntegerField()

如果你想更进一步，我建议你添加created_by和modified_by字段进行审计。

class TimeStampedModel(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    modified = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True

class TimeStampedAuthModel(TimeStampedModel):
    created_by = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, on_delete=models.SET_NULL,
                                   related_name="%(app_label)s_%(class)s_created_by")
    modified_by = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, on_delete=models.SET_NULL,
                                    related_name="%(app_label)s_%(class)s_modified_by")

    class Meta:
        abstract = True


class Vehicule(TimeStampedAuthModel):
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)

    class Meta:
        abstract = True


class WheeledVehicle(Vehicule):
    seats = models.PositiveSmallIntegerField()
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()

    class Meta:
        abstract = True


class Car(WheeledVehicle):
    year = models.IntegerField(default=2021, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    
    
class Truck(WheeledVehicle):
    year = models.IntegerField(default=datetime.now().year, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    bed_length = models.CharField(max_length=100)
    

class Boat(Vehicule):
    year = models.PositiveSmallIntegerField(default=datetime.now().year, validators=[MaxValueValidator(datetime.now().year)])
    length = models.CharField(max_length=100)
    width = models.CharField(max_length=100)
    HIN = models.CharField(max_length=14, validators=[MinLengthValidator(12)], blank=True)
    current_hours = models.PositiveSmallIntegerField()

【讨论】：

我也喜欢你把它分解成轮式车辆的方式。
我很高兴听到这个消息。不要忘记接受答案。问候！

【解决方案2】：

您可以使用model inheritance 或模型 Mixins

具有抽象基础模型的模型继承：

class AbstractVehicle(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    year = models.IntegerField(default=2021, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    
    class Meta:
        abstract = True

class Car(AbstractVehicle):
    seats = models.PositiveSmallIntegerField()    
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)


class Truck(AbstractVehicle):
    seats = models.PositiveSmallIntegerField()
    bed_length = models.CharField(max_length=100)
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)


class Boat(AbstractVehicle):
    length = models.CharField(max_length=100)
    width = models.CharField(max_length=100)
    HIN = models.CharField(max_length=14, validators=[MinLengthValidator(12)], blank=True)
    current_hours = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)

模型混合：

class VehicleMixin(object):
    created = models.DateTimeField(auto_now_add=True)
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    year = models.IntegerField(default=2021, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])

class Car(VehicleMixin, models.Model):
    seats = models.PositiveSmallIntegerField()    
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)


class Truck(VehicleMixin, models.Model):
    seats = models.PositiveSmallIntegerField()
    bed_length = models.CharField(max_length=100)
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)


class Boat(VehicleMixin, models.Model):
    length = models.CharField(max_length=100)
    width = models.CharField(max_length=100)
    HIN = models.CharField(max_length=14, validators=[MinLengthValidator(12)], blank=True)
    current_hours = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)

这两种解决方案都会为您提供与您的代码相同的表格。这些也只是简单的例子。您也许可以进一步改进它们。例如，您可以添加更多的 mixin 或包含其他字段的抽象基类。

【讨论】：

您知道这两种方法之间是否有任何优缺点？我正计划使用模型继承方法，但希望能够讨论使用 Mixins 的好处。
我相信这可能会对你有所帮助：stackoverflow.com/questions/3263417/…

【解决方案3】：

您可以通过创建Vehicle 和VehicleType 在保留所有常用车辆字段的车辆模型中组合模型，在VehicleType 保留汽车、卡车、船等，外键引用Vehicle 模型。

class VehicleType(models.Model):
    name = models.CharField(max_length=100, unique=True)
    created = models.DateTimeField(auto_now_add=True)

class Vehicle(models.Model):
    vehicle_type = models.Foreinkey(VehicleType, on_delete=model.CASCADE)
    created = models.DateTimeField(auto_now_add=True)
    make = models.CharField(max_length=100)
    model = models.CharField(max_length=100)
    year = models.IntegerField(default=datetime.now().year, validators=[MinValueValidator(1886), MaxValueValidator(datetime.now().year)])
    seats = models.PositiveSmallIntegerField()
    bed_length = models.CharField(max_length=100)
    color = models.CharField(max_length=100)
    VIN = models.CharField(max_length=17, validators=[MinLengthValidator(11)])
    current_mileage = models.PositiveSmallIntegerField()
    service_interval = models.CharField(max_length=50)
    next_service = models.CharField(max_length=50)

【讨论】：

那么 Car、Truck 和 Boat 模型只有一个对 Vehicle 的 foreignKey 引用？
不，这样可以让您只有一个表 Vehicle，其中每个条目可以是汽车、卡车或船。每个对象的类型将通过 vehicle_type ForeignKey 给出。