Dealing with unique constraints that should be replaced in django_rest_framework - django-rest-framework

Question

tl;dr: How can I ignore (turn off) a unique constraint in django_rest_framework Create calls with a ListCreateAPIView, because I'm going to deal with it manually in the perform_create method?
Im using a third party library django-push-notifications. It has a nice model for APNSDevice (apple push notification service device) that has a unique constraint on a registration_id field.
My problem is that sometimes I want to manually delete old values in the table that have the registration ID, so that I can insert a new value. I'd like to use this serializer:
class APNSDeviceSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = APNSDevice
fields = ('name', 'active', 'device_id', 'registration_id')
along with this code for PUT
class MyAppleDevices(generics.ListCreateAPIView):
permission_classes = (permissions.IsAuthenticated,)
serializer_class = APNSDeviceSerializer
model = APNSDevice
def get_queryset(self):
return APNSDevice.objects.filter(user = self.request.user)
def perform_create(self, serializer):
print "Looking for old devices with registration id "+str(self.request.registration_id)
oldDevices = APNSDevice.objects.filter(registration_id = self.request.registration_id)
for oldDevice in oldDevices:
oldDevice.delete()
apnsDevice = serializer.save(user=self.request.user)
In other words, I'm trying to manually delete other entries that have the unique constraint in this particular PUT, so that I can insert the new one without violating the unique constraint. The problem is the validator runs before the perform_create method is called, and I can't figure out how to turn off the validator's unique constraint. I tried adding this to the Serializer
def get_validation_exclusions(self, instance = None):
exclusions = super(APNSDeviceSerializer, self).get_validation_exclusions(instance)
return exclusions + ['registration_id']
but it doesn't help so obviously I have no clue even though I've been pouring through the documentation and Stack Overflow posts. Any help appreciated, thanks. I suppose as a last resort I could remove the unique constraint from the model, but it is a valid constraint so I'd rather leave it in.

Answer 1

I found this question because I had this exact problem with that exact library. You can get around it by subclassing the serializer and manually overriding the field definition:
class APNSDeviceSerializerWithNonUniqueRegistrationId(APNSDeviceSerializer):
registration_id = serializers.CharField(min_length=64, max_length=64)
class Meta(APNSDeviceSerializer.Meta):
fields = ("name", "registration_id", "device_id", "active", "date_created")
Then, if you're using django-push-notifications, you'll also need to override the ViewSet that uses that serializer:
class APNSDeviceAuthorizedViewSetWithNonUniqueRegistrationId(AuthorizedMixin, APNSDeviceViewSet):
"""
The out of the box viewset/serializer combo require the registration ID to be unique and won't
allow setting a registration ID to a new user (which is useful if we have potentially more than
one account on a device.)
"""
serializer_class = APNSDeviceSerializerWithNonUniqueRegistrationId
def perform_create(self, serializer):
if self.request.user.is_authenticated():
try:
existing_registration = APNSDevice.objects.get(
registration_id=serializer.validated_data['registration_id'])
existing_registration.delete()
except APNSDevice.DoesNotExist:
pass
serializer.save(user=self.request.user)
return super(DeviceViewSetMixin, self).perform_create(serializer)