Django管理外键下拉字段列表只有“测试对象”

I have these two classes:

我有这两个类：

class Test(models.Model):
    id = models.AutoField(primary_key=True)
    user = models.ForeignKey(User)
    groups = models.ManyToManyField(Group)

class TestSubjectSet(models.Model):
    id =  models.AutoField(primary_key=True)
    test = models.ForeignKey(Test)
    subject = models.ManyToManyField(Subject)
class Te