Django模型:两个类之间的相互引用以及在python中无法使用前向声明

2022-01-20 00:00:00 python django model foreign-keys forward-declaration

问题描述

我定义了两个模型，每个模型相互引用，如下所示:

I have defined two models where each one references the other, like so:

class User(models.Model):
    # ...
    loves = models.ManyToManyField(Article, related_name='loved_by')

class Article(models.Model):
    # ...
    author = models.ForeignKey(User)

你看，问题是两个类相互引用.无论这两个类以什么顺序实现，python总是引发NameError异常，抱怨一个类没有定义.

You see, the problem is both classes references each other. No matter in what order these two classes are implemented, python always raises NameError exception, complaining either one class is not defined.

解决方案

您可以在 文档:

如果您需要在尚未定义的模型上创建关系，您可以使用模型的名称，而不是模型对象本身:

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:

class Car(models.Model):
    manufacturer = models.ForeignKey('Manufacturer')
    # ...

class Manufacturer(models.Model):
    # ...

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