Django sort by distance

Question

I have the following model:

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

How should I make a query to sort by distance (distance is infinity)?

Working on PosgreSQL, GeoDjango if it is required.

Answer 1

Note: Please check cleder's answer below which mentions about deprecation issue (distance -> annotation) in Django versions.

First of all, it is better to make a point field instead of making lat and lnt separated:

from django.contrib.gis.db import models

location = models.PointField(null=False, blank=False, srid=4326, verbose_name='Location')

Then, you can filter it like that:

from django.contrib.gis.geos import Point
from django.contrib.gis.measure import D

distance = 2000 
ref_location = Point(1.232433, 1.2323232)

res = YourModel.objects.filter(
    location__distance_lte=(
        ref_location,
        D(m=distance)
    )
).distance(
    ref_location
).order_by(
    'distance'
)