Filtering several Geo near operations in a query sends an error

Question

I made a filter to do a Geospatial query on data from my Mongodb database and this filter works fine until I do an "And" operation on this filter with another Geospatial filter, but pointing to a different Property on the Collection I'm querying. When I add this filter, I get an Exception stating:

Message: MongoDB.Driver.MongoCommandException : Command find failed: Too many geoNear expressions.

Here is the first filter,

                var point = GeoJson.Point(GeoJson.Geographic(longitude: annEntityaAttr.CollectionLocation.Longitude,
                    latitude: annEntityaAttr.CollectionLocation.Latitude));
                filter = Builders<AnnouncementEntity>.Filter.Near(a => a.CollectionLocation, point, annEntityaAttr.MaxDistanceFromLocationInKM * metersFor1KM);

Here is how I add the second filter:

var point = GeoJson.Point(GeoJson.Geographic(longitude: annEntityaAttr.DepositLocation.Longitude,
                    latitude: annEntityaAttr.DepositLocation.Latitude));
                var secondFilter = Builders<AnnouncementEntity>.Filter.Near(a => a.DepositLocation, point, annEntityaAttr.MaxDistanceFromLocationInKM * metersFor1KM);

filter = filter & secondFilter;

Normaly, when applying & to two filters, it works, but in this case, it doesn't please does someone have a solution for this ?.

Answer 1

you can only do one geo query on a single collection at a time. if you must store two coordinate fields in a single document, you will have to issue two seperate geo queries and then intersect the results on the client side. also you'd need to create 2 geo indexes and specify the index key when querying. here's an example program that uses my library MongoDB.Entities to achieve what you need.

using MongoDB.Entities;
using MongoDB.Driver;
using System.Linq;

namespace StackOverflow
{
    public class Program
    {
        public class Announcement : Entity
        {
            public Coordinates2D CollectionLocation { get; set; }
            public Coordinates2D DepositLocation { get; set; }
            public double DistanceMeters { get; set; }
        }

        static void Main(string[] args)
        {
            new DB("test");

            DB.Index<Announcement>()
              .Key(a => a.CollectionLocation, KeyType.Geo2DSphere)
              .Create();

            DB.Index<Announcement>()
              .Key(a => a.DepositLocation, KeyType.Geo2DSphere)
              .Create();

            (new Announcement
            {
                DepositLocation = new Coordinates2D(48.8539241, 2.2913515),
                CollectionLocation = new Coordinates2D(48.796964, 2.137456)
            }).Save();

            var searchPointA = new Coordinates2D(48.796964, 2.137456);

            var queryA = DB.GeoNear<Announcement>(
                                NearCoordinates: searchPointA,
                                DistanceField: a => a.DistanceMeters,
                                IndexKey: "CollectionLocation",
                                MaxDistance: 10);

            var searchPointB = new Coordinates2D(48.8539241, 2.2913515);

            var queryB = DB.GeoNear<Announcement>(
                                NearCoordinates: searchPointB,
                                DistanceField: a => a.DistanceMeters,
                                IndexKey: "DepositLocation",
                                MaxDistance: 10);

            var resultA = queryA.ToList();
            var resultB = queryB.ToList();

            var common = resultA.Where(a => resultB.Any(b => b.ID == a.ID)).ToArray();
        }
    }
}

the following two $geoNear queries will be issued to find the locations:

[
    {
        "$geoNear": {
            "near": {
                "type": "Point",
                "coordinates": [
                    48.8539241,
                    2.2913515
                ]
            },
            "distanceField": "DistanceMeters",
            "spherical": true,
            "maxDistance": NumberInt("10"),
            "key": "DepositLocation"
        }
    }
]

[
    {
        "$geoNear": {
            "near": {
                "type": "Point",
                "coordinates": [
                    48.796964,
                    2.137456
                ]
            },
            "distanceField": "DistanceMeters",
            "spherical": true,
            "maxDistance": NumberInt("10"),
            "key": "CollectionLocation"
        }
    }
]