mongodb - 在 MongoDB 中查询一个 ArrayPosition

Question

我有一个这样的集合:

> db.nodes.find()  
{ "_id" : ObjectId("534d44e182bee8420ace927f"), "id" : "59598841", "created_by" : "JOSM", "geo" : { "type" : "Point", "coordinates" : [ 9.7346094, 52.371738 ] } }  
{ "_id" : ObjectId("534d44e182bee8420ace9280"), "id" : "59598842", "created_by" : "JOSM", "geo" : { "type" : "Point", "coordinates" : [ 9.7343616, 52.3718121 ] } }  
{ "_id" : ObjectId("534d44e182bee8420ace9281"), "id" : "59598845", "created_by" : "JOSM", "geo" : { "type" : "Point", "coordinates" : [ 9.7331504, 52.372057 ] } }  
{ "_id" : ObjectId("534d44e182bee8420ace9282"), "id" : "59835778", "created_by" : "JOSM", "geo" : { "type" : "Point", "coordinates" : [ 9.7354137, 52.3711697 ] } }  
{ "_id" : ObjectId("534d44e182bee8420ace9283"), "id" : "60409270", "created_by" : "JOSM", "geo" : { "type" : "Point", "coordinates" : [ 9.7354388, 52.3735999 ] } }  

现在我想查询坐标数组以找到具有最大 lon 值的文档。我该怎么做，我不知道:(

楚斯，安德烈

Answer 1

因此实际上获取数组的第一个值“lon”可能看起来并不明显，但使用聚合非常简单:

db.nodes.aggregate([
    { "$project": {
        "_id": {
          "_id": "$_id",
          "id": "$id",
          "created_by": "$created_by",
          "geo": "$geo",
        },
        "coordinates": "$geo.coordinates"
    }},
    { "$unwind": "$coordinates" },
    { "$group": {
        "_id": "$_id",
        "lon": { "$first": "$coordinates" }
    }},
    { "$sort": { "lon": 1 } },
    { "$limit": 1 },   
    { "$project": {
        "_id": "$_id._id",
          "id": "$_id.id",
          "created_by": "$_id.created_by",
          "geo": "$_id.geo",
    }}
])

它给出了整个文档的最高值。或者，如果您只想要值:

db.nodes.aggregate([
    { "$unwind": "$geo.coordinates" },
    { "$group": {
        "_id": "$_id",
        "lon": { "$first": "$geo.coordinates" }
    }},
    { "$group": {
        "_id": null,
        "lon": { "$max": "$lon" }
    }}
])