Question

I am using mongodb-engine to access MongoDB from a Django project. Normal get, insert and update works quite well, but now would I like to use the geoNear functionality. I can just not figure out a way to call it from Django.

I have tried MyModel.objects.raw(...) and also MyModel.objects.raw_query(...), but the result is not really as expected.

The query will be something like this one (it works from the Mongo shell)

db.runCommand({ geoNear : "mymodel", near : [3, 0], spherical : true, maxDistance : 10 })

And the model uses MongoDBManager

class MyModel(model.Model):
    objects = MongoDBManager()
    ...

has anyone successfully tried that?

Thx Simon

Answer 1

I guess the use of the MongoDB db.runCommand(), which is needed for queries with geoNear, is just not possible with the current version of mongodb-enginge. I am using a raw_query with the normal near syntax now and convert the distance between the 2 lat/lon points myself to miles (and the other way around).

lat_lon_dist = distance_to_lat_long(dist_in_miles)
l = Listing.objects.raw_query({
                       'geo_location' : {
                                     '$maxDistance': lat_lon_dist,
                                     '$near' : { 'latitude': lat, 'longitude': lon },
                                     }
                       })
...
EARTH_RADIUS = { 
                'km': 6371, 
                'mi': 3959 
                }

''' returns the distance between two lat/lon points in miles or kilometers '''
def lat_lon_to_distance(lat1, lon1, lat2, lon2, unit='mi'):
    lat1 = math.radians(lat1)
    lon1 = math.radians(lon1)
    lat2 = math.radians(lat2)
    lon2 = math.radians(lon2)
    return math.acos(math.sin(lat1)*math.sin(lat2) + 
                  math.cos(lat1)*math.cos(lat2) *
                  math.cos(lon2-lon1)) * EARTH_RADIUS[unit];

'''
converts a distance in miles or kilometer to a difference between two lat/lon points
the result is just approximately!
'''
def distance_to_lat_long(distance, unit='mi'):
    return distance / math.radians(EARTH_RADIUS[unit])