SpatialLite backend raises ValueError when getting distance parameter.

[tcourtqtm]

I'm experiencing a ValueError from the SpatiaLite backend. When doing a query like this:

MyModel.objects.filter(point__dwithin = (some_point, D(km=distance_in_km)))

I am getting this error:

ValueError: Only numeric values of degree units are allowed on geographic DWithin queries.

This does not happen with the PostGIS backend and I believe it's a bug.

After a bit of searching I noticed that the difference between the two backends is that postgis has a conditional to check if the PointField is geographic and, if it is, avoids the exception.

The ​code from the postgis backend:

        if isinstance(value, Distance):
            if geography:
                dist_param = value.m
            elif geodetic:
                if lookup_type == 'dwithin':
                    raise ValueError('Only numeric values of degree units are '
                                     'allowed on geographic DWithin queries.')
                dist_param = value.m
            else:
                dist_param = getattr(value, Distance.unit_attname(f.units_name(self.connection)))

And the ​same function from the spatialite backend:

        if isinstance(value, Distance):
            if f.geodetic(self.connection):
                if lookup_type == 'dwithin':
                    raise ValueError(
                        'Only numeric values of degree units are allowed on '
                        'geographic DWithin queries.'
                    )
                dist_param = value.m
            else:
                dist_param = getattr(value, Distance.unit_attname(f.units_name(self.connection)))

I am very unfamiliar with Geo stuff in general but this looks like a simple omission in the spatialite code. I believe it should have a similar if geography check.

[Mariusz Felisiak]

geography columns are supported only on PostGIS, also an example from the ticket description works on SpatiaLite (see ​similar tests).