MongoDB and .netCore Find nearest locations (unable to find index for $geoNear query)

Question

I'm trying to find nearest other locations form my MongoDB database.

I'm using .net Core as rest API.

.net Core 5.0

This is my MDB Class

public class MdbTrip
{
        [BsonId]
        [BsonRepresentation(MongoDB.Bson.BsonType.ObjectId)]
        public string id { get; set; }

        public GeoJsonPoint<GeoJson2DGeographicCoordinates> location { get; set; }

}

This is the way I fond to make the query (To find nearest other locations within 200m).

 var point = GeoJson.Point(GeoJson.Geographic(myLocation.lng, myLocation.lat));
 var locationQuery = new FilterDefinitionBuilder<MdbTrip>().Near(tag => tag.location, point, 200);
 var c = _trips.Find(locationQuery).ToList();

_trips is Injected with a interface and it represents IMongoCollection.

My objects are saving perfectly find in the database (DB connection is fine).

But When I try to find other near location this error comes.

MongoDB.Driver.MongoCommandException: 'Command find failed: error processing query: ns=VtrackDB.MdbTripTree: GEONEAR  field=location maxdist=200 isNearSphere=0
Sort: {}
Proj: {}
 planner returned error :: caused by :: unable to find index for $geoNear query.'

In this Line

var c = _trips.Find(locationQuery).ToList();

I'm bit new to .net core and MongoDB.

Let me know how to fix this issue (Where I make my wrong turn).

Answer 1

_trips.Indexes.CreateManyAsync(
    new[]
    {
        new CreateIndexModel<MdbTrip>(Builders<MdbTrip>.IndexKeys.Geo2DSphere(it => it.location))
    }
);

This fixed my issue.

I put it before this.

var point = GeoJson.Point(GeoJson.Geographic(myLocation.lng, myLocation.lat));

I found the solution form -> MongoDb C# GeoNear Query Construction

Please, Anyone who knows the reason explain.

Thank you.