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- $geoNear (aggregation)
$geoNear (aggregation)¶
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Definition¶
- $geoNear¶
2.4 新版功能.
Outputs documents in order of nearest to farthest from a specified point.
The $geoNear stage has the following prototype form:
{ $geoNear: { <geoNear options> } }
The $geoNear operator accepts a document that contains the following $geoNear options. Specify all distances in the same units as those of the processed documents’ coordinate system:
Field Type Description spherical boolean Required if using a 2dsphere index. Determines how MongoDB calculates the distance. The default value is false.
If true, then MongoDB uses spherical geometry to calculate distances in meters if the specified (near) point is a GeoJSON point and in radians if the specified (near) point is a legacy coordinate pair.
If false, then MongoDB uses 2d planar geometry to calculate distance between points.
If using a 2dsphere index, spherical must be true.
limit number Optional. The maximum number of documents to return. The default value is 100. See also the num option. num number Optional. The num option provides the same function as the limit option. Both define the maximum number of documents to return. If both options are included, the num value overrides the limit value. maxDistance number Optional. The maximum distance from the center point that the documents can be. MongoDB limits the results to those documents that fall within the specified distance from the center point.
Specify the distance in meters for GeoJSON data and in radians for legacy coordinate pairs.
query document Optional. Limits the results to the documents that match the query. The query syntax is the usual MongoDB read operation query syntax.
You cannot specify a $near predicate in the query field of the $geoNear stage.
distanceMultiplier number Optional. The factor to multiply all distances returned by the query. For example, use the distanceMultiplier to convert radians, as returned by a spherical query, to kilometers by multiplying by the radius of the Earth. uniqueDocs boolean Optional. If this value is true, the query returns a matching document once, even if more than one of the document’s location fields match the query.
2.6 版后已移除: Geospatial queries no longer return duplicate results. The $uniqueDocs operator has no impact on results.
near GeoJSON point or legacy coordinate pair The point for which to find the closest documents.
If using a 2dsphere index, you can specify the point as either a GeoJSON point or legacy coordinate pair.
If using a 2d index, specify the point as a legacy coordinate pair.
distanceField string The output field that contains the calculated distance. To specify a field within an embedded document, use dot notation. includeLocs string Optional. This specifies the output field that identifies the location used to calculate the distance. This option is useful when a location field contains multiple locations. To specify a field within an embedded document, use dot notation. minDistance number Optional. The minimum distance from the center point that the documents can be. MongoDB limits the results to those documents that fall outside the specified distance from the center point.
Specify the distance in meters for GeoJSON data and in radians for legacy coordinate pairs.
3.2 新版功能.
Behavior¶
When using $geoNear, consider that:
- You can only use $geoNear as the first stage of a pipeline.
- You must include the distanceField option. The distanceField option specifies the field that will contain the calculated distance.
- The collection must have a geospatial index.
- The $geoNear requires that a collection have at most only one 2d index and/or only one 2dsphere index.
- You do not need to specify which field in the documents hold the coordinate pair or point. Because $geoNear requires that the collection have a single geospatial index, $geoNear implicitly uses the indexed field.
- If using a 2dsphere index, you must specify spherical: true.
- You cannot specify a $near predicate in the query field of the $geoNear stage.
- Views do not support geoNear operations (i.e. geoNear command and $geoNear pipeline stage)
Generally, the options for $geoNear are similar to the geoNear command with the following exceptions:
Example¶
Consider a collection places that has a 2dsphere index. The following aggregation finds at most 5 unique documents with a location at most 2 units from the center [ -73.99279 , 40.719296 ] and have type equal to public:
db.places.aggregate([
{
$geoNear: {
near: { type: "Point", coordinates: [ -73.99279 , 40.719296 ] },
distanceField: "dist.calculated",
maxDistance: 2,
query: { type: "public" },
includeLocs: "dist.location",
num: 5,
spherical: true
}
}
])
The aggregation returns the following:
{
"_id" : 8,
"name" : "Sara D. Roosevelt Park",
"type" : "public",
"location" : {
"type" : "Point",
"coordinates" : [ -73.9928, 40.7193 ]
},
"dist" : {
"calculated" : 0.9539931676365992,
"location" : {
"type" : "Point",
"coordinates" : [ -73.9928, 40.7193 ]
}
}
}
The matching document contains two new fields:
- dist.calculated field that contains the calculated distance, and
- dist.location field that contains the location used in the calculation.
Minimum Distance¶
3.2 新版功能.
The following example uses the option minDistance to specify the minimum distance from the center point that the documents can be. MongoDB limits the results to those documents that fall outside the specified distance from the center point.
db.places.aggregate([
{
$geoNear: {
near: { type: "Point", coordinates: [ -73.99279 , 40.719296 ] },
distanceField: "dist.calculated",
minDistance: 2,
query: { type: "public" },
includeLocs: "dist.location",
num: 5,
spherical: true
}
}
])