C# MongoDB "Near"查询

Question

我有一个mongo集合，看起来像这样:

{
"_id": {
    "$oid": "50e9f38fbd7680c8090bcb4"
},
"guid": "D3G5wQ8RZL",
"lat": 37.503287248864,
"lng": -121.97620341421,

}我想使用c# linq

执行"NEAR"查询

应该是这样的

query = query.Where(x => LinqToMongo.Inject(Query.Near("Location", -96.770401, 32.816774, 20)));

我的问题是-我应该写什么而不是"位置"?我如何查看上述集合中的点数?

谢谢。

Answer 1

从MongoDB 2.4开始，存储和索引GeoJSON。你可以在这里找到所有的概念。

如何在POCO类型上定义GeoJSON属性:

public class Foo
{
  public GeoJsonPoint<GeoJson2DGeographicCoordinates> Location { get; set; }
}

一个实例化的例子:

var docToInsert = new Foo
            {   
                Location = new GeoJsonPoint<GeoJson2DGeographicCoordinates>(
                    new GeoJson2DGeographicCoordinates(-121.97620341421, 37.503287248864))
            });

$near需要一个地理空间索引，因为我们存储的是GeoJSON，所以它特别需要一个2dsphere索引:

var collection = //get MongoCollection<Foo> from MongoDatabase object
collection.EnsureIndex(IndexKeys<Foo>.GeoSpatialSpherical(x => x.Location));

现在查询:

var point = GeoJson.Point(GeoJson.Geographic(-96.770401, 32.816774)); //long, lat
var locationClause = Query<Foo>.Near(y=> y.Location, point, 20); //20 is max distance from your question. note that it's in meters
IQueryable<Foo> query = collection.AsQueryable().Where( x=> locationClause.Inject()); 
//or with the non-generic Query:  
IQueryable<Foo> query = collection.AsQueryable().Where( x=> Query.Near("Location", point, 20).Inject());