Question

我是MongoDb的新手，希望您对此查询有所帮助。我写了以下聚合管道

db.collection1.aggregate([
    { "$match": { "type" : "L" }},
    { "$facet": {
        "ON": [
            { "$match" : {"lampStatus":'ON'}},
            { "$count": "ON" }
        ],
        "OFF": [
            { "$match" : {"lampStatus": 'OFF'}},
            { "$count": "OFF" }
        ]
    } },
    { "$project": {
        "ON": { "$ifNull": [{ "$arrayElemAt": ["$ON.ON", 0] }, 0 ] },
        "OFF": { "$ifNull": [{ "$arrayElemAt": ["$OFF.OFF", 0] }, 0 ] },
    } }
])

并获得此类型的输出

{
    "ON" : 0.0,
    "OFF": 30
}

但是如何获取json格式的此类输出

/* 1 */ 
{ 
    "_id": "ON", 
    "count" : 0.0 
} 

/* 2 */ 
{ 
    "_id": "OFF", 
    "count" : 30.0 
}

有人建议我吗？

实际输出

{
    "ON" : 0.0,
    "OFF" : 30
}

预期输出：

{
    "_id" : "ON",
    "COUNT" : 0.0
}

/* 2 */
{
    "_id" : "OFF",
    "COUNT" : 30.0
}

Answer 1

已更新

db.collection.aggregate([
    { "$match": { "type" : "L" }},
    { "$facet": {
        "ON": [
            { "$match" : {"lampStatus":'ON'}},
            { "$count": "ON" }
        ],
        "OFF": [
            { "$match" : {"lampStatus": 'OFF'}},
            { "$count": "OFF" }
        ]
    } },
    {"$project": { 
            myArray: [ 
                {_id:"ON", count: { "$ifNull": [{ "$arrayElemAt": ["$ON.ON", 0] }, 0 ]} },
                {_id:"OFF", count: { "$ifNull": [{ "$arrayElemAt": ["$OFF.OFF", 0] }, 0 ] }}
        ] 
        }},

        {"$unwind":"$myArray"},

        {
            "$replaceRoot": { newRoot: "$myArray" }
        }

])

Answer 2

如果您需要更多聚合技巧

db.collection1.aggregate([
  { "$match": { "type" : "L" }},
  { "$facet": {
    "ON": [{ "$match" : {"lampStatus": "ON" }}, { "$count": "ON" }],
    "OFF": [{ "$match" : {"lampStatus": "OFF" }}, { "$count": "OFF" }]
  }},
  { "$project": {
    "ON": { "$ifNull": [{ "$arrayElemAt": ["$ON.ON", 0] }, 0 ] },
    "OFF": { "$ifNull": [{ "$arrayElemAt": ["$OFF.OFF", 0] }, 0 ] },
  }},
  { "$project": {
    "data": {
      "$map": { "input": { "$objectToArray": "$$ROOT" }, "in": { "_id": "$$this.k", "count": "$$this.v" }}
    }
  }},
  { "$unwind": "$data" },
  { "$replaceRoot": { "newRoot": "$data" }}
])

如何更改MongoDB输出JSON格式

2 个答案: