检索ManyToManyField类

Question

考虑到以下简化模型，我需要返回一个ManyToManyField的空ManyToManyField，但是我收到一个"AttributeError：'ReverseManyRelatedObjectsDescriptor‘对象没有属性'none'“

class AnimalFamily(models.Model):
  objects = GetOrNoneManager()
  siblings = objects.none()


class Countable(models.Model):
  @classmethod
  def get_peers(cls_obj,target_animal):
    animals = cls_obj.objects.get_or_none(siblings=target_animal)
    if animals:
      return animals.siblings.exclude(id=target_animal.id)
    else
      return cls_obj.siblings.none()    # <--- this fails <----

  class Meta:
    abstract = True


class BearFamily(AnimalFamily,Countable):
  siblings = models.ManyToManyField(Bear)

class GiraffeFamily(AnimalFamily,Countable):
  siblings = models.ManyToManyField(Giraffe)


class Bear(models.Model):
  pass

class Giraffe(models.Model):
  pass

如何访问泛型类方法中的"Bear"-Class或相应的“长颈鹿”-Class以返回正确QuerySet的空查询？

额外信息：

# dir(cls_obj.siblings) returns:
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__get__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__set__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'field', 'related_manager_cls', 'through']

Answer 1

错误消息明确指出了一个问题，即您要返回的对象没有名为"none“的属性。这可能就是你想要的：

if animals:
  return animals.siblings.exclude(id=target_animal.id)
else
  cls_obj.siblings = []   
  return cls_obj.siblings