Django sort by distance

Question

I have the following model:

class Vacancy(models.Model):
    lat = models.FloatField(\'Latitude\', blank=True)
    lng = models.FloatField(\'Longitude\', bla         


        

Answer 1

On Django 3.0 there will be a GeometryDistance function, which works the same way as Distance, but uses the <-> operator instead, which uses spatial indexes on ORDER BY queries, eliminating the need for a dwithin filter:

from django.contrib.gis.db.models.functions import GeometryDistance
from django.contrib.gis.geos import Point

ref_location = Point(140.0, 40.0, srid=4326)
Vacancy.objects.annotate(
    distance=GeometryDistance('location', ref_location)
).order_by('distance')

If you want to use it before Django 3.0 is released, you could use something like this:

from django.contrib.gis.db.models.functions import GeoFunc
from django.db.models import FloatField
from django.db.models.expressions import Func

class GeometryDistance(GeoFunc):
   output_field = FloatField()
   arity = 2
   function = ''
   arg_joiner = ' <-> '
   geom_param_pos = (0, 1)

   def as_sql(self, *args, **kwargs):
       return Func.as_sql(self, *args, **kwargs)