python - django 模型中的 m2m 'through' 字段抛出此错误 : 'M2M field' object has no attribute '_m2m_reverse_name_cache'

Question

嘿伙计们，我正在尝试添加一个 m2m through领域让我的“部门”模型的助手像 department.assistants.all() 一样打电话，但这样做时，我收到此错误 AttributeError: 'ManyToManyField' object has no attribute '_m2m_reverse_name_cache' .
这是我的模型:

class Department(models.Model):
    id                  = models.BigAutoField(primary_key=True)
    user                = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    assistants          = models.ManyToManyField(settings.AUTH_USER_MODEL, through='Assistants', related_name='dep_assistants', 
                            symmetrical=False)

class Assistants(models.Model):
    id                  = models.BigAutoField(primary_key=True)
    department          = models.ForeignKey(Department, related_name='of_department', on_delete=models.CASCADE)
    assistant           = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='dt_assistant', 
                            verbose_name="Department Assistant", on_delete=models.CASCADE)
    added               = models.DateTimeField(auto_now_add=True)

我对这个概念很陌生。有人能告诉我我在这里做错了什么吗？
谢谢

Answer 1

您定义模型的方式查询似乎太困惑了。尝试在下面如何定义模型，然后尝试查询。
您没有在多对多字段定义中提及 through_field 属性。检查文档:https://docs.djangoproject.com/en/3.2/ref/models/fields/#django.db.models.ManyToManyField

class Department(models.Model):
    # i think this is not needed. Also id is a protected keyword in python.
    # id                  = models.BigAutoField(primary_key=True)
    user                = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    assistants          = models.ManyToManyField(settings.AUTH_USER_MODEL, through='Assistants', 
                                                 related_name='departments', through_fields=("department", "assistant"))

# model name should never be prural. It is singluar becuase it is the name of the object.
class Assistant(models.Model):
    # i think this is not needed. Also id is a protected keyword in python.
    # id                  = models.BigAutoField(primary_key=True)
    department          = models.ForeignKey(Department, on_delete=models.CASCADE)
    assistant           = models.ForeignKey(settings.AUTH_USER_MODEL, verbose_name="Department Assistant", on_delete=models.CASCADE)
    added               = models.DateTimeField(auto_now_add=True)


# how to query assistants from departments
# you will get objects of User model
qs = department.assistants.all()


# how to query departments from assistants
# you will get objects of Department model
qs = user.departments.all()


# If you want to query the Assistant model

# from department object
qs = department.assistant_set.all()

# from assistant object
qs = user.assistant_set.all()

# in either case you will get the objects of Assistant model
for i in qs:
    print(i.added, i.department, i.assistant)

试试这个，如果你仍然收到错误，请告诉我。
我的建议是命名 assistant Assistant 模型上的字段为 user .这样你就不需要定义 through_field在多对多领域。