Closest location (lat & long) with Postgresql in Django

README.md

Distance calculation

Example how to calculate distance and then take closest location.

Can be further imporved by first filtering locations to some square withing min & max lat & long. So we are not calculating distance for all locations.

I know you could use some greate Geo engine for PostgreSQL or Django but I needed fast, working solution. Feel free to use

License

MIT

migrations.py

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import models, migrations


class Migration(migrations.Migration):

    dependencies = [
        ('locations', '0001_initial'),
    ]

    operations = [
        migrations.RunSQL("""
            CREATE OR REPLACE FUNCTION distance(lat1 FLOAT, lon1 FLOAT, lat2 FLOAT, lon2 FLOAT) RETURNS FLOAT AS $$
            DECLARE
                x float = 69.1 * (lat2 - lat1);\
                y float = 69.1 * (lon2 - lon1) * cos(lat1 / 57.3);\
            BEGIN
                RETURN sqrt(x * x + y * y);\
            END
            $$ LANGUAGE plpgsql;\
        """)
    ]

models.py

from django.db.models.base import Model
from django.db.models.fields import CharField, IntegerField, DecimalField
from django_extensions.db.fields.json import JSONField

class LocationModel(Model):
    name = CharField(max_length=255)
    english_name = CharField(max_length=255)
    country = CharField(max_length=255)
    location_id = IntegerField(primary_key=True)
    lat = DecimalField(max_digits=20, decimal_places=10)
    long = DecimalField(max_digits=20, decimal_places=10)
    viewport = JSONField()
    
    @classmethod
    def closest(cls, lat, long):
        locations = LocationModel.objects.extra(
            select={
                'distance': 'distance(lat, long, %f, %f)' % (lat, long)
            }
        )
        locations = locations.order_by('distance')
        return locations.first()