show distance in km or m of each restaurant

Question

I have implemented the feature of showing nearby restaurant from the given coordinates using postgis and geodjango. But I need to find the distance in km or m based on the distance it is nearby from user or given coordinates. I know question related to distance is asked in SO but this one is a bit different. I am showing the list of restaurant(list view) not a detail of restaurant that I will have specific restaurant location from the id. So i need an idea how should I now show the distance for each restaurant in the restaurant list view.

My idea is should I pass the lat and lng(that I am passing from the url) as context and use template filter for calculating the distance by doing

from django.contrib.gis.geos import GEOSGeometry
pnt = GEOSGeometry('SRID=4326;POINT(40.396764 -3.68042)')
pnt2 = GEOSGeometry('SRID=4326;POINT( 48.835797 2.329102  )')
pnt.distance(pnt2)*100

Here is the code in detail

def nearby_restaurant_finder(request, current_lat, current_long):
    from django.contrib.gis.geos import Point
    from django.contrib.gis.measure import D

    user_location = Point(float(current_long), float(current_lat))
    distance_from_point = {'km': 500}
    restaurants = Restaurant.gis.filter(
        location__distance_lte=(user_location, D(**distance_from_point)))
    restaurants = restaurants.distance(user_location).order_by('distance')
    context = {
        'restaurants': restaurants
    }
    return render(request, 'restaurant/nearby_restaurant.html', context)


 url(r'^nearby_restaurant/(?P<current_lat>-?\d*.\d*)/(?P<current_long>-?\d*.\d*)/$',
        views.nearby_restaurant_finder, name="nearby-restaurant"),


{% block page %}
    {% for restaurant in restaurants %}
        <h1>Nearby Restaurants are:</h1>
        <h3>{{ restaurant.name }}</h3>
        {% empty %}
        <h3>No Match Found</h3>
    {% endfor %}
{% endblock %}

Please share your idea on how should i do it

Answer 1

I think you're almost there; I would calculate the distance using python and then display them in the template instead of creating a filter.

I would first update the context with a list of dictionaries or similar:

def calculate_distance(restaurant_location, current_lat, current_long):
    # this function should return the distance of the restaurant from the user
    return distance_calculated

def nearby_restaurant_finder(request, current_lat, current_long):
    from django.contrib.gis.geos import Point
    from django.contrib.gis.measure import D

    user_location = Point(float(current_long), float(current_lat))
    distance_from_point = {'km': 500}
    restaurants = Restaurant.gis.filter(location__distance_lte=(user_location, D(**distance_from_point)))
    restaurants = restaurants.distance(user_location).order_by('distance')

    # create a list of dictionaries with results to display
    ctx_restaurants = [
        {
            'name': restaurant.name, 
            'distance_from_user': calculate_distance(restaurant.location, current_lat, current_long)
        }
        for restaurant in restaurants
    ]

    # pass results into context
    context = {
        'restaurants': ctx_restaurants
    }
    return render(request, 'restaurant/nearby_restaurant.html', context)

Then I would render this in the template in some sort of table

{% block page %}
    <h1>Nearby Restaurants are:</h1>
    <table>
    {% for restaurant in restaurants %}
        <tr>
        <td>{{ restaurant.name }}</td>
        <td>{{ restaurant.distance_from_user}}</td>
        </tr>
    {% endfor %}
    </table>
{% endblock %}

Using TDD: Since the calculate_distance() is decoupled, I would test it by passing a bunch of known distances. Set up your tests according to the testing docs

from django.test import TestCase
from myapp.views import calculate_distance

class DistanceTests(TestCase):
    def setUp(self):
        self.known_cases = [
            {'location': XX1, 'lat': XX1, 'long': XX1, 'expected': XX1},
            {'location': XX2, 'lat': XX2, 'long': XX2, 'expected': XX2},
        ]

    def test_calculate_distance(self):
        for case in self.known_cases:
            self.assertEquals(
                calculate_distance(case['location'], case['lat'], case['long']),
                case['expected']
            )