E TypeError：禁止直接分配到多对多集的前向端。使用 subject.set() 代替

Question

我正在编写一些 api 调用的测试，我遇到的问题是我无法弄清楚如何在 Django 中分配多对多变量（主题）。

models.py

class Subject(BaseModel):
    id = models.AutoField(primary_key=True)
    name = models.TextField(null=False, blank=False)
    answers = models.ManyToManyField("registration.Answer", through="AnswerSubject")


class Answer(BaseModel):
    id = models.AutoField(primary_key=True)
    text = models.TextField(null=False, blank=False)
    subjects = models.ManyToManyField("subjects.Subject", through="subjects.AnswerSubject")

test.py

def tets_get_answer:
  Answer.objects.create(
        text=f'{"test answer"}',
        subjects = f{"test subject"} # the error is here, how do I assign subjects?
    ),
    ........

这是我收到的错误：

E       TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use subjects.set() instead.

Any help is appreciated

Answer 1

您创建一个 Subject 模型，并在稍后进行设置：

def test_get_answer(self):
    answer = Answer.objects.create(
        text='test answer',
        # no subjects
        # …
    )
    subject = Subject.objects.create(
        name='test subject'
    )
    answer.subjects.add(subject)

但是，没有理由定义 ManyToManyField 两次：如果您在 Django 中定义一个关系，Django 也会自动定义一个关系相反。您可以使用 lated_name=… 参数 [Django-doc]：

class Subject(BaseModel):
    name = models.TextField()
    # no answers


class Answer(BaseModel):
    text = models.TextField()
    subjects = models.ManyToManyField(
        Subject,
        through='subjects.AnswerSubject',
        related_name='answers'
    )