MongoDb AND GeoSpatial Query

[Mark Towse]

I am trying to do GeoSpatial Queries on MongoDb using the C# driver.  I have a document as follows:

    public class Journey// IJourney

    {

        public ObjectId Id { get; set; }

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

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

      

    }

And I have written a method which performs the following.

    var point = GeoJson.Point(GeoJson.Geographic(-0.1258020000000215, 51.44695)); //long, lat

    var point2 = GeoJson.Point(GeoJson.Geographic(-0.1258020000000215, 51.44695)); //long, lat

    Collection.CreateIndex(IndexKeys<Journey>.GeoSpatialSpherical(x => x.Start));

    Collection.CreateIndex(IndexKeys<Journey>.GeoSpatialSpherical(x => x.End));

    var startQuery = Query<Journey>.Near(y => y.Start, point, 1950);

    var endQuery = Query<Journey>.Near(y => y.End, point2, 1);

    var t = Query.And(startQuery, endQuery);

            

    IQueryable<T> query = Collection.AsQueryable().Where(x => t.Inject());

    return query.ToList<T>();

I am trying to find Journeys which have a start x distance from point one and an end x distance from point 2.  The above query produces the following.

    { "Start" : { "$near" : { "$geometry" : { "type" : "Point", "coordinates" :               [-0.12580200000002151,       51.44695] } }, "$maxDistance" : 1950.0 }, "End" : { "$near" : {    "$geometry" : { "type" : "Point",  "coordinates" : [-0.12580200000002151, 51.44695] } }, "$maxDistance" : 1.0 } }

My data has only 1 row with the end coordinates which meets the query.  When I run this query I get 8 rows which is what meets the start query parameter.  If I comment out the startQuery and just run it with the end one I get one row as exected.  It appears to be doing an OR when I specify Query.And and I don't know why.  How do I make it do an AND?

According to this mongo blog what I am trying to achieve should be possible.

http://blog.mongodb.org/post/50984169045/new-geo-features-in-mongodb-2-4

"Additionally, we can have multiple 2dsphere indexes in the same compound index. This allows queries like: “Find routes with a start location within 50 miles from JFK, and an end location within 100 miles of YYC”."

[Asya Kamsky]

If you want to find 

> Journeys which have a start x distance from point one and an end x distance from point 2

then you should use $geoWithin and *not* $near.   Near will sort results by distance, nearest to furtherest and you have *two* $near operator creating a bit of an undefined scenario.   Using $within is something that can be done for more than one point, logically speaking.   In addition, this will be faster than $near as it doesn't have to produce results in a specific order.

Asya

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