Django rest api - searching a method field with the search filter

Question

im trying to filter search a rest api page and want to use a method field as one of the search fields, however when I do this I get an error stating the field is not valid and it then lists the field in my model as the only valid source

serialiser:

class SubnetDetailsSerializer(QueryFieldsMixin, serializers.HyperlinkedModelSerializer):
    subnet = serializers.SerializerMethodField()
    device = serializers.ReadOnlyField(
        source='device.hostname',
    )
    circuit_name = serializers.ReadOnlyField(
        source='circuit.name',
    )
    subnet_name = serializers.ReadOnlyField(
        source='subnet.description',
    )
    safe_subnet = serializers.SerializerMethodField()

    def get_safe_subnet(self, obj):
        return '{}{}'.format(obj.subnet.subnet, obj.subnet.mask.replace('/','_')) 

    def get_subnet(self, obj):
        return '{}{}'.format(obj.subnet.subnet, obj.subnet.mask) 

    class Meta:
        model = DeviceCircuitSubnets   
        fields = ('id','device_id','subnet_id','circuit_id','subnet','safe_subnet','subnet_name','device','circuit_name') 

views:

class SubnetDetailsSet(viewsets.ReadOnlyModelViewSet):
    queryset = DeviceCircuitSubnets.objects.all().select_related('circuit','subnet','device')
    serializer_class = SubnetDetailsSerializer
    permission_classes = (IsAdminUser,)
    filter_class = DeviceCircuitSubnets
    filter_backends = (filters.SearchFilter,)
    search_fields = (
        'device__hostname',
        'circuit__name',
        'subnet__subnet',
        'safe_subnet'
    )

how can include the safe_subnet in the search fields?

Thanks

EDIT This is the code now

views.py

class SubnetDetailsSet(viewsets.ReadOnlyModelViewSet):
    queryset = DeviceCircuitSubnets.objects.all()
    serializer_class = SubnetDetailsSerializer
    permission_classes = (IsAdminUser,)
    filter_class = DeviceCircuitSubnets
    filter_backends = (filters.SearchFilter,)
    search_fields = (
        'device__hostname',
        'circuit__name',
        'subnet__subnet',
        'safe_subnet'
    )

    def get_queryset(self):
        return (
            super().get_queryset()
            .select_related('circuit','subnet','device')
            .annotate(
                safe_subnet=Concat(
                    F('subnet__subnet'),
                    Replace(F('subnet__mask'), V('/'), V('_')),
                    output_field=CharField()
                )
            )
        )

serializer.py

class SubnetDetailsSerializer(QueryFieldsMixin, serializers.HyperlinkedModelSerializer):
    subnet = serializers.SerializerMethodField()
    device = serializers.ReadOnlyField(
        source='device.hostname',
    )
    circuit_name = serializers.ReadOnlyField(
        source='circuit.name',
    )
    subnet_name = serializers.ReadOnlyField(
        source='subnet.description',
    )
    def get_safe_subnet(self, obj):
        return getattr(obj, 'safe_subnet', None)

    def get_subnet(self, obj):
        return '{}{}'.format(obj.subnet.subnet, obj.subnet.mask) 

    class Meta:
        model = DeviceCircuitSubnets   
        fields = ('id','device_id','subnet_id','circuit_id','subnet','safe_subnet','subnet_name','device','circuit_name')  

Model:

class DeviceCircuitSubnets(models.Model):
    device = models.ForeignKey(Device, on_delete=models.CASCADE)
    circuit = models.ForeignKey(Circuit, on_delete=models.CASCADE, blank=True, null=True)
    subnet = models.ForeignKey(Subnet, on_delete=models.CASCADE)
    active_link = models.BooleanField(default=False, verbose_name="Active Link?")
    active_link_timestamp = models.DateTimeField(auto_now=True, blank=True, null=True)

Error:

Exception Type: ImproperlyConfigured at /api/subnets/
Exception Value: Field name `safe_subnet` is not valid for model `DeviceCircuitSubnets`.

Answer 1

Going in a completely different direction from the other (excellent) answers. Since you want to be able to filter frequently on the safe_subnet field, why not just let it be an actual database field in your model? You could calculate and populate/update the value during one of your save methods and then just let django-filters do it's thing. This also has the advantage of allowing the filtering to be done directly through SQL which would theoretically provide better performance.