我想將約束添加到涉及對另一個模型對象的引用的模型上。在下面的代碼中，我希望在 ProjectMember 模型上， project_member 字段被限制為與項目模型中的 project_creator 不同。class User(models.Model):  fullname = models.CharField(max_length=200)  email = models.EmailField(max_length=254)  password = models.CharField(max_length=254)class Project(models.Model):  name = models.CharField(max_length=200)  timestamp = models.DateTimeField("date created", auto_now=True)  project_creator = models.ForeignKey(User, on_delete=models.CASCADE)class ProjectMember(models.Model):  project = models.ForeignKey(Project, on_delete=models.CASCADE)  project_member = models.ForeignKey(      User,      on_delete=models.CASCADE,      verbose_name="member of the project"  )  class Meta:      order_with_respect_to = 'user_member'      constraints = [          models.CheckConstraint(check= ,              name='project creator not project member'),      ]