Django 模型 - 循环导入问题

Question

我的 Django 项目使用三个应用程序，chat, user, sowi. 每个应用程序都有按以下方式构造的模型。启动服务器时出现错误，我认为这是因为我有循环导入。我该如何解决这个问题？

聊天/models.py

from user.models import User

class Chat(models.Model):
    name = models.CharField(max_length=100, default="private")


class Message(models.Model):
    sender = models.ForeignKey(User, on_delete=models.CASCADE)
    receiver = models.ForeignKey(Chat, on_delete=models.CASCADE)

用户/模型.py

from chat.models import Chat
from sowi.models import Sowi

class User(AbstractUser):
    chats = models.ManyToManyField(Chat, blank=True)
    subscriptions = models.ManyToManyField(Sowi, related_name="subscriptions", blank=True)
    memberships = models.ManyToManyField(Sowi, related_name="memberships", blank=True)
    blocked = models.ManyToManyField("self", related_name="blocked", blank=True)

sowi/models.py

from chat.models import Chat, Message
from user.models import User

class Sowi(models.Model):
    owner = models.ForeignKey(User, on_delete=models.CASCADE)
    chat = models.OneToOneField(Chat, blank=True, null=True, on_delete=models.CASCADE)

错误信息：

File "*/sowi/models.py", line 9, in <module>
    from chat.models import Chat, Message
  File "*/chat/models.py", line 4, in <module>
    from user.models import User
  File "*/user/models.py", line 5, in <module>
    from chat.models import Chat
ImportError: cannot import name 'Chat' from 'chat.models'

提前致谢！

Answer 1

最好使用字符串文字来引用模型，而不是通过对模型类的引用来引用模型。Django 可以处理这个问题并会自动解决这些问题：

# chat/models.py

from django.db import models

class Chat(models.Model):
    name = models.CharField(max_length=100, default="private")

class Message(models.Model):
    sender = models.ForeignKey('user.User', on_delete=models.CASCADE)
    receiver = models.ForeignKey(Chat, on_delete=models.CASCADE)

# user/models.py

from django.db import models

class User(AbstractUser):
    chats = models.ManyToManyField(Chat, blank=True)
    subscriptions = models.ManyToManyField('sowi.Sowi', related_name="subscriptions", blank=True)
    memberships = models.ManyToManyField('sowi.Sowi', related_name="memberships", blank=True)
    blocked = models.ManyToManyField("self", related_name="blocked", blank=True)

# sowi/models.py

from django.db import models

class Sowi(models.Model):
    owner = models.ForeignKey('user.User', on_delete=models.CASCADE)
    chat = models.OneToOneField('chat.Chat', blank=True, null=True, on_delete=models.CASCADE)

更好的是，您引用用户模型 [Django-doc]来设置AUTH_USER_MODEL设置 [Django-doc]，并使用此设置，这样如果您以后改变主意，可以更方便地更改此设置：

# chat/models.py

from django.conf import settings
from django.db import models

class Chat(models.Model):
    name = models.CharField(max_length=100, default="private")

class Message(models.Model):
    sender = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    receiver = models.ForeignKey(Chat, on_delete=models.CASCADE)

# user/models.py

from django.db import models

class User(AbstractUser):
    chats = models.ManyToManyField(Chat, blank=True)
    subscriptions = models.ManyToManyField('sowi.Sowi', related_name="subscriptions", blank=True)
    memberships = models.ManyToManyField('sowi.Sowi', related_name="memberships", blank=True)
    blocked = models.ManyToManyField("self", related_name="blocked", blank=True)

# sowi/models.py

from django.conf import settings
from django.db import models

class Sowi(models.Model):
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    chat = models.OneToOneField('chat.Chat'