Django REST Framework Partial update and validation

Question

I want to perform a partial update on my serializer. The problem is that I have a some validation at object level. So the is_valid() call always fails and I can't save the the updated serializer. Can I somehow prevent the object level validation on partial updates? Here a code sample:

class ModelSerializer(serializers.ModelSerializer)
    class Meta:
        model = A
        fields = ('field_b','field_b')

    def validate(self,attrs):
         if attrs.get('field_a') <= attrs.get('field_b'):
             raise serializers.ValidationError('Error')

And in my viewset the partial update method:

class ModelViewSet(viewsets.ModelViewSet):
    def partial_update(self, request, *args, **kwargs):
        instance = self.get_object()
        serializer = self.serialize(instance, data=request.data, partial=True)
    serializer.is_valid(raise_exception=True)
    new_instance = serializer.save()
    return Response(serializer.data)

The problem ist that I cannot update 'field_a' without 'field_b'. Thanks for your help!

Please mention what do you mean by object level validation? Please post some code to understand clearly. — Antony
– Antony, Commented Feb 27, 2015 at 12:42
The documentation mentions two types of validation, "field-level" and "object-level". django-rest-framework.org/api-guide/serializers/#validation For the "object-level" validation I need a full object with all fields. So I think it shoudn't be called for partial updates. But is_valid() always fails because of the object level validation — ilse2005
– ilse2005, Commented Mar 4, 2015 at 14:30
I believe django rest framework has a formal solution to this now. Please check django-rest-framework.org/api-guide/serializers/…. — Reetesh Ranjan
– Reetesh Ranjan, Commented Jun 6, 2016 at 17:27

Mark Chackerian · Accepted Answer · 2020-04-13 22:21:04Z

14

self.instance is how to access the instance in the validator. Here's an example:

def validate_my_field(self, value):
    """ Can't modify field's value after initial save """
    if self.instance and self.instance.my_field != value:
        raise serializers.ValidationError("changing my_field not allowed")
    return value

edited Apr 13, 2020 at 22:21

answered Sep 1, 2015 at 20:28

Mark Chackerian

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Comments

Pavel · Accepted Answer · 2016-11-29 07:59:12Z

0

You can use the "partial" argument in order to allow partial updates: http://www.django-rest-framework.org/api-guide/serializers/#partial-updates

answered Nov 29, 2016 at 7:59

Pavel

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