Django filter location distance with dynamic radius

Question

I have 2 model in django a zone and a shop, models are like this:

from django.contrib.gis.db import models
from django.contrib.gis.geos import Point
from dja         


        

Answer 1

That seems to happen inside the MeasureBase class of django.contrib.gis.measure (which Distance/D inherits from) and more specifically in the default_units method where it tries to cast str or numeric input values to float but receives an F expression instead.

What we can do as a workaround, is to annotate the Distance (careful with this Distance method because it comes from the GeoDjango Geographic Database Functions) between the shop.location_point and the current location_point and then we can filter by that distance being <= than the instance radius:

from django.contrib.gis.db.models.functions import Distance

zone_list = Zone.objects.annotate(
    distance=Distance('location_point', shop.location_point)
).filter(distance__lte=F('radius'))

Kudos to this excellent answer from @e4c5: GeoDjango filter by distance from a model field

Another approach would be to eliminate the annotation part entirely and go straight to the filtering by Distance:

from django.contrib.gis.db.models.functions import Distance

zone_list = Zone.objects.filter(
    radius_gte=Distance('location_point', shop.location_point)
)

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I leave this here for comment continuity:

You can try to cast the F('radius') result as a FloatField() using the Cast() method to turn the Integer to a Float.

zone_list = Zone.objects.filter(
    location_point__distance_lte=(
        shop.location_point, 
        D(m=Cast('radius', output_field=models.FloatField()))
    )
)