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coordinates-array以找到具有最大lon-value的文档。我怎么能这样做，我不知道:(

Tschüss，Andre

Answer 1

所以实际上得到数组的第一个值“lon”可能看起来不是很明显，但聚合很简单：

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",
    }}
])

这为整个文档提供了最高的价值。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" }
    }}
])

Answer 2

尝试使用聚合框架

db.nodes.aggregate(
 { $unwind: "geo.coordinate" },
 { $group: { _id: { id: "$id"}, lon: { $first: "geo.coordinate" } } },
 { $group: { _id: null, maxval: { $max: "$lon" } } }
)

有关聚合的更多信息，请查看此处：http://docs.mongodb.org/manual/reference/operator/aggregation/

查询MongoDB中的ArrayPosition

2 个答案: