$maxDistance

Definition定义

$maxDistance

The $maxDistance operator constrains the results of a geospatial $near or $nearSphere query to the specified distance. $maxDistance运算符将地理空间$near或$nearSphere查询的结果约束为指定的距离。The measuring units for the maximum distance are determined by the coordinate system in use. 最大距离的测量单位由使用中的坐标系确定。For GeoJSON point objects, specify the distance in meters, not radians. 对于GeoJSON点对象，以米为单位指定距离，而不是弧度。You must specify a non-negative number for $maxDistance.必须为$maxDistance指定一个非负数。

The 2dsphere and 2d geospatial indexes both support $maxDistance: .2dsphere和2d地理空间索引都支持$maxDistance:。

Example实例

The following example query returns documents with location values that are 10 or fewer units from the point [ -74 , 40 ].以下示例查询返回的文档的位置值从点[ -74 , 40 ]算起不超过10个单位。

db.places.find( {
   loc: { $near: [ -74 , 40 ],  $maxDistance: 10 }
} )

MongoDB orders the results by their distance from [ -74 , 40 ]. MongoDB根据它们与[ -74 , 40 ]之间的距离对结果进行排序。The operation returns the first 100 results, unless you modify the query with the cursor.limit() method.除非使用cursor.limit()方法修改查询，否则该操作将返回前100个结果。