JSONField and Dynamic filters

[moweerkat]

Hello there,

Not really an issue, more like a beginner of a solution for those who rack their brains on how how programmatically setup filters in different situations.

My need is this one: I'm using a JSONField to store data according to what the user specified in a configuration. It means I can't know in advance what are the "subfields" inside the json.

Model example:

class MyModel(models.Model):

name = models.CharField()
data = JSONField()

What's inside the data could be something like:

{
  "price": 12.23,
  "invoice": "/tmp/invoice.pdf"
  "foo": "bar"
}

And it's always the same in all objects.

As I want to be able to filter such a field, I'm setting up a FilterSet with a custom method and add some logic in the constructor as such:

FilterSet

class MyModelFilterSet(FilterSet):
    def filter_json_field_value(self, queryset, name, value):
        return queryset.filter(**{name: value})

    class Meta:
        model = models.MyModel
        fields = ["created", "modified"]

def __init__(self, *args, **kwargs):
        """Based on instance, add according filters."""
        super(CModelItemFilter, self).__init__(*args, **kwargs)

        if self.queryset.exists():
            lookup_expressions = [
                "icontains",
                "contains",
                "exact",
                "..." ,
            ]
            data = self.queryset.first().data
            for key, value in data.items():
                for lookup in lookup_expressions:
                    if isinstance(value, float):
                        self.base_filters[f"{key}__{lookup}"] = NumberFilter(
                            field_name=f"data__{key}__{lookup}",
                            method="filter_json_field_value",
                        )
                    elif isinstance(value, str):
                        self.base_filters[f"{key}__{lookup}"] = CharFilter(
                            field_name=f"data__{key}__{lookup}",
                            method="filter_json_field_value",
                        )
                   else:
                     ...

Viewset

class MyModelViewset(viewsets.ModelViewSet):
    """A viewset for handling MyModel."""

    queryset = models.MyModel.objects.all()
    permission_classes = [IsAdminUser]
    serializer_class = serializers.MyModelSerializer
    filter_backends = [DjangoFilterBackend]
    filterset_class = MyModelFilterSet

I can now filter as such:

api/mymodels/?price__exact=12
api/mymodels/?invoice__isnull=false
api/mymodels/?foo__startswith=b&foo__endswith=r&created__gte=..."

Now, I didn't do a benchmark. I'm sure it can quickly become an abyss with too many lookup expressions and data fields. But with some more logic to not add all the lookup expressions, it should be ok.

Hope it helps.