Mongodb 检索动态子文档密钥

我有这个mongo文件

{
    "name": "aaa",
    "Time": "Now",
    "_id": "656i9gfk543klffx",
    "lastReadings": {
        "7-Temperature": {
            "_t": "NumberReading",
            "timestamp": "2017-02-13T12:51:50.000+0000",
            "unit": "C",
            "typeCode": 7,
            "name": "Temperature",
            "numberValue": 11.271406207825713
        },
        "30-DISCONNECT": {
            "_t": "NumberReading",
            "internalTimestamp": "2017-06-02T19:16:33.050+0000",
            "timestamp": "2017-06-02T19:16:27.147+0000",
            "unit": "",
            "typeCode": 30,
            "name": "DISCONNECT",
            "numberValue": 1
        }
    }
},
{
    "name": "aaa",
    "Time": "Now",
    "_id": "gtrg565opgf0",
    "lastReadings": {
        "7-Temperature": {
            "_t": "NumberReading",
            "timestamp": "2017-02-13T12:51:50.000+0000",
            "unit": "C",
            "typeCode": 7,
            "name": "Temperature",
            "numberValue": 46
        },
        "25-Water": {
            "_t": "NumberReading",
            "internalTimestamp": "2017-06-02T19:16:33.050+0000",
            "timestamp": "2017-06-02T19:16:27.147+0000",
            "unit": "",
            "typeCode": 25,
            "name": "Water",
            "numberValue": 1
        }
    }
}

我试图从“LastReaders”对象中获取不同的字段键，其中“name”字段等于“aaa”。 因此，我预期的结果将是：

["7-Temperature", "30-DISCONNECT","25-Water"]

“lastReadings”中的子对象键是动态的，我不知道它们的名称以及“lastReadings”中有多少个文件

我可以通过什么聚合查询来实现此结果

我已经回答了这个问题：

{$match: {"name":"aaa"}},
{ $group: { _id: "name", mergedEvents: { $mergeObjects: "$lastReadings" } } }

但是当我有很多文档时，它似乎运行得很慢（在“LastReads”上建立索引会提高性能吗？），并且它会返回整个不必要的对象

---

谢谢。

好吧，我们可以通过以下管道来实现这一点：

[
   {
      "$group":{
         "_id":null,
         "lastReadings":{
            "$push":{
               "$map":{
                  "input":{
                     "$objectToArray":"$lastReadings"
                  },
                  "in":"$$this.k"
               }
            }
         }
      }
   },
   {
      "$project":{
         "mergeEvent":{
            "$reduce":{
               "input":"$lastReadings",
               "initialValue":[

               ],
               "in":{
                  "$setUnion":{
                     "$concatArrays":[
                        "$$this",
                        "$$value"
                     ]
                  }
               }
            }
         }
      }
   }
]

但是，我建议您检查模式设计并删除动态字段的名称

“LastReaders”字段可能如下所示：

{
   "lastReadings":[
      {
         "parameter":"7-Temperature",
         "value":{
            "_t":"NumberReading",
            "timestamp":"2017-02-13T12:51:50.000+0000",
            "unit":"C",
            "typeCode":7,
            "name":"Temperature",
            "numberValue":11.271406207825713
         }
      },
      {
         "parameter":"30-DISCONNECT",
         "value":{
            "_t":"NumberReading",
            "internalTimestamp":"2017-06-02T19:16:33.050+0000",
            "timestamp":"2017-06-02T19:16:27.147+0000",
            "unit":"",
            "typeCode":30,
            "name":"DISCONNECT",
            "numberValue":1
         }
      }
   ]
}

使用这种模式，您可以使用

.disctinct

方法和点表示法检索不同的值

db.collection.distinct("lastReadings.parameter")