Django Rest Framework PUT request on unique model field

Question

I have the following model

class Owner(models.Model):
    user    = models.OneToOneField(User, default=1, editable=True)
    phone   = models.CharField(max_length=40, null=True, blank=True)
    address = models.CharField(max_length=255, null=True, blank=True)
    city    = models.CharField(max_length=255, null=True, blank=True)
    state   = USStateField(null=True, blank=True)
    zip     = models.CharField(max_length=20, null=True, blank=True)

    def __str__(self):
        return "%s %s" % (self.user.first_name, self.user.last_name)


class Device(CreationModificationMixin):

    _STATUSES = (
        ('A', 'Active'),
        ('I', 'Inactive'),
        ('F', 'Failure'),
    )

    _TYPES = (
        ('S', 'Spa'),
        ('P', 'Pool'),
    )

    udid    = models.CharField(max_length=255, verbose_name="Unique ID / MAC Address", null=False, blank=False, unique=True)
    type    = models.CharField(max_length=1, choices=_TYPES, null=False, blank=False)
    title   = models.CharField(max_length=255, null=False, blank=False)
    status  = models.CharField(max_length=1, default='A', choices=_STATUSES)
    pinged  = models.DateTimeField(null=True)
    owner   = models.ForeignKey(Owner, verbose_name="Owner", null=True, blank=True)

    def __str__(self):
        return self.udid

I have the following serializer

class DeviceSerializer(serializers.ModelSerializer):

    class Meta:
        model = Device
        fields = ('id', 'udid', 'title', 'type', 'status', 'pinged', 'created')

I have the following API View defined:

class DeviceAPIView(APIView):
    permission_classes = (IsAuthenticated,) # explicit
    code_404 = "Device doesn't exists"

    def get(self, request, device_id):

        try:
            d = Device.objects.get(id=device_id, owner=request.user.owner)
        except Device.DoesNotExist:
            return Response({'error': self.code_404}, 404)

        serializer = DeviceSerializer(d)
        return Response(serializer.data)

    def put(self, request, device_id):

        serializer = DeviceSerializer(data=request.DATA)

        if not serializer.is_valid():
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
        else:
            data = serializer.data
            data['id'] = id
            d = Device(**data).save()
            serializer = DeviceSerializer(d)
            return Response(serializer.data, status=status.HTTP_200_OK)

PUT request on existing device

{
    "udid": "38-2C-4A-47-C2-ED",
    "title": "Backyard pool",
    "type": "S"
} 

gives me back

{
    "udid": ["This field must be unique."]
}

However I'm updating the record and passing the same UDID it has. So I'm not getting a duplicate in DB but DRF thinks the other way.

What I need to achieve is

• If UDID of the same record is not changed - then no error should be raised
• if UDID of the record changes and now it's the same as some of record's UDID then error should be returned.

Answer 1

As per the comments implementing the put method closer to the reference implementation in the docs should fix the issue.

def put(self, request, pk, format=None):
    device = self.get_object(pk)
    serializer = DeviceSerializer(device, data=request.data)
    if serializer.is_valid():
        serializer.save()
        return Response(serializer.data)
    return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

Saving instances has a bit more information on creating, updating and saving instances by using the serializer class methods.