[英]How to get the old values of django model field while updating without using signals in django rest framework?
I am using django-rest-framework. 我正在使用django-rest-framework。 I have a case in which I need to update the field of other model once instance of first model is created or updated. 我有一种情况,一旦创建或更新了第一个模型的实例,就需要更新其他模型的字段。
here is my models.py: 这是我的models.py:
class FirstModel(models.Model):
first_model_item = models.ForeignKey(Item)
quantity = models.IntegerField()
class SecondModel(models.Model):
second_model_item = models.ForeignKey(FirstModel)
quantity = models.IntegerField()
Here is my views.py: 这是我的views.py:
class CreateSecondModelView(generics.CreateAPIView):
permission_classes = ()
queryset = SecondModel.objects.all()
serializer_class = SecondModeSerializer
def perform_create(self, serializer):
instance = serializer.save()
first_model_item = instance.item
first_model_item.quantity -= instance.quantity
first_model_item.save()
class UpdateSecondModelView(generics.RetrieveUpdateAPIView):
permission_classes = ()
queryset = SecondModel.objects.all()
serializer_class = SecondModeSerializer
def perform_update(self, serializer):
instance = serializer.save()
#here i want old value of quantity before updating.
The serializer has an instance attribute, which is not updated until you call save. 序列化程序具有实例属性,该属性在您调用保存之前不会更新。 So: 所以:
old_quantity = serializer.instance.quantity
instance = serializer.save()
new_quantity = instance.quantity
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