# Aggregate.geoNear(options: Object): Aggregate

支持端：小程序 2.7.4, 云函数 0.8.1, Web

聚合阶段。将记录按照离给定点从近到远输出。

# 参数

# options: Object

属性	类型	必填	说明
near	GeoPoint	是	GeoJSON Point，用于判断距离的点
spherical	true	是	必填，值为 true
limit	number	否	限制返回记录数
maxDistance	number	否	距离最大值
minDistance	number	否	距离最小值
query	Object	否	要求记录必须同时满足该条件（语法同 where）
distanceMultiplier	number	否	返回时在距离上乘以该数字
distanceField	string	是	存放距离的输出字段名，可以用点表示法表示一个嵌套字段
includeLocs	string	否	列出要用于距离计算的字段，如果记录中有多个字段都是地理位置时有用
key	string	否	选择要用的地理位置索引。如果集合由多个地理位置索引，则必须指定一个，指定的方式是指定对应的字段

# 返回值

# Aggregate

# API 说明

geoNear 必须为第一个聚合阶段
必须有地理位置索引。如果有多个，必须用 key 参数指定要使用的索引。

# 示例

假设集合 attractions 有如下记录：

{
  "_id": "geoNear.0",
  "city": "Guangzhou",
  "docType": "geoNear",
  "location": {
    "type": "Point",
    "coordinates": [
      113.30593,
      23.1361155
    ]
  },
  "name": "Canton Tower"
},
{
  "_id": "geoNear.1",
  "city": "Guangzhou",
  "docType": "geoNear",
  "location": {
    "type": "Point",
    "coordinates": [
      113.306789,
      23.1564721
    ]
  },
  "name": "Baiyun Mountain"
},
{
  "_id": "geoNear.2",
  "city": "Beijing",
  "docType": "geoNear",
  "location": {
    "type": "Point",
    "coordinates": [
      116.3949659,
      39.9163447
    ]
  },
  "name": "The Palace Museum"
},
{
  "_id": "geoNear.3",
  "city": "Beijing",
  "docType": "geoNear",
  "location": {
    "type": "Point",
    "coordinates": [
      116.2328567,
      40.242373
    ]
  },
  "name": "Great Wall"
}

const $ = db.command.aggregate
db.collection('attractions').aggregate()
  .geoNear({
    distanceField: 'distance', // 输出的每个记录中 distance 即是与给定点的距离
    spherical: true,
    near: db.Geo.Point(113.3089506, 23.0968251),
    query: {
      docType: 'geoNear',
    },
    key: 'location', // 若只有 location 一个地理位置索引的字段，则不需填
    includeLocs: 'location', // 若只有 location 一个是地理位置，则不需填
  })
  .end()

返回结果如下：

{
  "_id": "geoNear.0",
  "location": {
    "type": "Point",
    "coordinates": [
      113.30593,
      23.1361155
    ]
  },
  "docType": "geoNear",
  "name": "Canton Tower",
  "city": "Guangzhou",
  "distance": 4384.68131486958
},
{
  "_id": "geoNear.1",
  "city": "Guangzhou",
  "location": {
    "type": "Point",
    "coordinates": [
      113.306789,
      23.1564721
    ]
  },
  "docType": "geoNear",
  "name": "Baiyun Mountain",
  "distance": 6643.521654040738
},
{
  "_id": "geoNear.2",
  "docType": "geoNear",
  "name": "The Palace Museum",
  "city": "Beijing",
  "location": {
    "coordinates": [
      116.3949659,
      39.9163447
    ],
    "type": "Point"
  },
  "distance": 1894750.4414538583
},
{
  "_id": "geoNear.3",
  "docType": "geoNear",
  "name": "Great Wall",
  "city": "Beijing",
  "location": {
    "type": "Point",
    "coordinates": [
      116.2328567,
      40.242373
    ]
  },
  "distance": 1928300.3308822548
}