使用ManyToManyField验证祖父母内的唯一性

Question

我试图验证一个模型，指定父母模型的ManyToManyField在祖父母模型中是唯一的。如果不同的祖父母有同名的孙辈，但祖父母可能没有两个同名的孙辈，这很好。

This question讨论一个解决方案，如果关系是ForignKey s，但在这里不起作用。在我可以参考父母进行测试以确定其是否在GrandParent内是唯一的之前，GrandChild必须得到保存。

由于父母在GrandChild存在之前不能附属，所以GrandChild的独特性如何与GrandParent进行验证？

class GrandParent(models.Model): 
    name = models.CharField(max_length=255) 

class Parent(models.Model): 
    name = models.CharField(max_length=255) 
    grandparent = models.ForeignKey(GrandParent) 

    class Meta: 
     unique_together('name', 'GrandParent')  

class GrandChild(models.Model): 
    name = models.CharField(max_length=255) 
    parents = models.ManyToManyField(Parent) 

    def validate_unique(self, exclude=None): 
     # validate that GrandChild is unique within a given GrandParent 

我尝试添加了save()方法给孙子方法

def save(self, *args, **kwargs): 
    grand_parent = self.parents.all()[0].grandparent 
    grand_children = [child for child in parent.grandchild_set.all() for parent in grandparent.parent_set.all()] 

    for grand_child in grand_children: 
     if grand_child.name == self.name and grand_child != self: 
      raise IntegrityError("must be unique") 

但是，这给了IntegrityError

ValueError: "<GrandChild: name>" needs to have a value for field "grandchild" before this many-to-many relationship can be used. 

Answer 1

def save(self, *args, **kwargs): 
    grand_parent_id = kwargs.pop('grand_parent_id') 
    if grand_parent_id is None: 
     raise SomeException(...) 
    grand_parent = GrandParent.objects.get(pk=grand_parent_id) 
    for parent in grand_parent.parent_set.all(): 
     for grand_child in parent.grandchild_set.all(): 
      if grand_child.name == self.name: 
       raise IntegrityError("Name must be unique") 

# views.py 
grand_parent = get_object_or_404(GrandParent, pk=kwargs.get('grand_parent_pk')) 
if form.is_valid(): 
    form.save(grand_parent_id=grand_parent.pk)