与Django中抽象模型相关的ForeignKey字段
问题内容：
我有这个模型：
class BaseModel(models.Model):
....
class Meta:
abstract = True
class ModelA(BaseModel):
....
class ModelB(BaseModel):
....
class MyExtModel(models.Model)
myfield = models.ForeignKey(BaseModel)
但这是不正确的，因为我BaseModel喜欢Abstract。实际上，尝试makemigration命令时出现错误。
错误是：
ERRORS:
myapp.MyExtModel.myfield: (fields.E300) Field defines a relation with model 'BaseModel', which is either not installed, or is abstract.
有没有一种使用抽象基础模型的方法？
我也尝试使用：
myfield = models.ForeignKey(BaseModel, related_name="%(app_label)s_%(class)s_related")
问题答案：
在Django中无法将外键安装到抽象模型。但是，您可以将外键安装到非抽象基类。唯一的限制是反向外键关系将返回基类实例。您可以使用django-
polymorphic
来规避此限制。
Django Polymorphic允许您查询基类对象，但可以检索子类实例：
>>> Project.objects.create(topic="Department Party")
>>> ArtProject.objects.create(topic="Painting with Tim", artist="T. Turner")
>>> ResearchProject.objects.create(topic="Swallow Aerodynamics", supervisor="Dr. Winter")
>>> Project.objects.all()
[ <Project: id 1, topic "Department Party">,
<ArtProject: id 2, topic "Painting with Tim", artist "T. Turner">,
<ResearchProject: id 3, topic "Swallow Aerodynamics", supervisor "Dr. Winter"> ]
要使用django多态，只需要声明以Polymorphic Model为基类的模型即可：
from django.db import models
from polymorphic.models import PolymorphicModel
class ModelA(PolymorphicModel):
field1 = models.CharField(max_length=10)
class ModelB(ModelA):
field2 = models.CharField(max_length=10)
class ModelC(ModelB):
field3 = models.CharField(max_length=10)
外键还将返回子类实例，这是您需要的：
# The model holding the relation may be any kind of model, polymorphic or not
class RelatingModel(models.Model):
many2many = models.ManyToManyField('ModelA') # ManyToMany relation to a polymorphic model
>>> o=RelatingModel.objects.create()
>>> o.many2many.add(ModelA.objects.get(id=1))
>>> o.many2many.add(ModelB.objects.get(id=2))
>>> o.many2many.add(ModelC.objects.get(id=3))
>>> o.many2many.all()
[ <ModelA: id 1, field1 (CharField)>,
<ModelB: id 2, field1 (CharField), field2 (CharField)>,
<ModelC: id 3, field1 (CharField), field2 (CharField), field3 (CharField)> ]
