Django模型子类化与方法重写问题：基类迭代调用子类方法失效

问题根源 #

你的原始代码使用Django多表继承时，Owner.objects.all()返回的是Owner类实例，而非子类Industry/Household的实例，因此调用的是基类的dothis方法；此外子类方法中直接引用size/population会触发NameError，需改为self.size/self.population。

一、将Owner设为抽象基类的标准方法 #

Django中创建抽象模型基类无需继承Python的ABC/ABCMeta，只需在模型的Meta类中设置abstract=True，基类不会生成数据库表，子类自动继承其方法与字段。

修正代码：

from django.db import models

class Owner(models.Model):
    def dothis(self):
        print('base class dothis was called')

    class Meta:
        abstract = True  # 标记为抽象基类

class Industry(Owner):
    size = models.IntegerField(default=1)
    def dothis(self):
        print(f'Industry dothis says {self.size}')

class Household(Owner):
    population = models.IntegerField(default=1)
    def dothis(self):
        print(f'Household dothis says {self.population}')

def do():
    Industry.objects.create(size=1)
    Household.objects.create(population=2)
    # 抽象基类无数据库表，需合并子类查询结果
    all_owners = list(Industry.objects.all()) + list(Household.objects.all())
    for owner in all_owners:
        owner.dothis()

执行后会输出：

Industry dothis says 1
Household dothis says 2

二、替代方案：多表继承+向下转型 #

若需保留Owner的数据库表（用于存储公共字段），可通过多表继承自动生成的一对一关联字段获取子类实例：

from django.db import models

class Owner(models.Model):
    def dothis(self):
        # 检测并调用子类方法
        if hasattr(self, 'industry'):
            self.industry.dothis()
        elif hasattr(self, 'household'):
            self.household.dothis()
        else:
            print('base class dothis was called')

class Industry(Owner):
    size = models.IntegerField(default=1)
    def dothis(self):
        print(f'Industry dothis says {self.size}')

class Household(Owner):
    population = models.IntegerField(default=1)
    def dothis(self):
        print(f'Household dothis says {self.population}')

def do():
    Industry.objects.create(size=1)
    Household.objects.create(population=2)
    for owner in Owner.objects.all():
        owner.dothis()

此方案下，Owner.objects.all()返回的基类实例会自动转发调用子类的dothis方法。

内容的提问来源于stack exchange，提问作者ancient geek