Node.js MongoDB对子文档数组的查询和投影也会返回另一个文档的数组

我试图查询嵌入的子文档，然后通过返回该子文档中的数组。查询后，您可以选择希望通过投影返回的字段。我想使用本机功能，因为这是可能的，也是最干净的方式。问题是它返回两个文档中的数组

我尝试了不同的查询和投影选项，但没有结果

用户模型

             // Define station schema
             const stationSchema = new mongoose.Schema({
                mac: String,
                stationName: String,
                syncReadings: Boolean,
                temperature: Array,
                humidity: Array,
                measures: [{
                    date: Date,
                    temperature: Number,
                    humidity: Number
                }],
                lastUpdated: Date
            });

            // Define user schema
            var userSchema = mongoose.Schema({

                apiKey: String,
                stations : [stationSchema]

            },  {
                    usePushEach: true 
                }
            );

       app.get('/api/stations/:stationName/measures',function(req, res, next) {

        var user = {
            apiKey: req.user.apiKey
        }

        const query = {
            apiKey: user.apiKey,
            'stations.stationName': req.params.stationName
        }

        const options = {
            'stations.$.measures': 1,
        }

        User.findOne(query, options)
        .exec()
        .then(stations => {     
            res.status(200).send(stations)
        })
        .catch(err => {
            console.log(err);
            res.status(400).send(err);
        })

    });

api调用

             // Define station schema
             const stationSchema = new mongoose.Schema({
                mac: String,
                stationName: String,
                syncReadings: Boolean,
                temperature: Array,
                humidity: Array,
                measures: [{
                    date: Date,
                    temperature: Number,
                    humidity: Number
                }],
                lastUpdated: Date
            });

            // Define user schema
            var userSchema = mongoose.Schema({

                apiKey: String,
                stations : [stationSchema]

            },  {
                    usePushEach: true 
                }
            );

       app.get('/api/stations/:stationName/measures',function(req, res, next) {

        var user = {
            apiKey: req.user.apiKey
        }

        const query = {
            apiKey: user.apiKey,
            'stations.stationName': req.params.stationName
        }

        const options = {
            'stations.$.measures': 1,
        }

        User.findOne(query, options)
        .exec()
        .then(stations => {     
            res.status(200).send(stations)
        })
        .catch(err => {
            console.log(err);
            res.status(400).send(err);
        })

    });

预期结果

   {
        "_id": "5c39c99356bbf002fb092ce9",
        "stations": [
            {
                "stationName": "livingroom",
                "measures": [
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:45.468Z",
                        "_id": "5c3a6f09fd357611f8d078a0"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:46.500Z",
                        "_id": "5c3a6f0afd357611f8d078a1"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:47.041Z",
                        "_id": "5c3a6f0bfd357611f8d078a2"
                    }
                ]
            }
        ]
    }

   {
        "_id": "5c39c99356bbf002fb092ce9",
        "stations": [
            {
                "stationName": "livingroom",
                "measures": [
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:45.468Z",
                        "_id": "5c3a6f09fd357611f8d078a0"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:46.500Z",
                        "_id": "5c3a6f0afd357611f8d078a1"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:47.041Z",
                        "_id": "5c3a6f0bfd357611f8d078a2"
                    }
                ]
            },
******************************************************
 // this whole object should not be returned
            {
              "stationName": "office",
                "measures": [] 
            }
******************************************************
        ]
    }

实际结果

   {
        "_id": "5c39c99356bbf002fb092ce9",
        "stations": [
            {
                "stationName": "livingroom",
                "measures": [
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:45.468Z",
                        "_id": "5c3a6f09fd357611f8d078a0"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:46.500Z",
                        "_id": "5c3a6f0afd357611f8d078a1"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:47.041Z",
                        "_id": "5c3a6f0bfd357611f8d078a2"
                    }
                ]
            }
        ]
    }

   {
        "_id": "5c39c99356bbf002fb092ce9",
        "stations": [
            {
                "stationName": "livingroom",
                "measures": [
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:45.468Z",
                        "_id": "5c3a6f09fd357611f8d078a0"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:46.500Z",
                        "_id": "5c3a6f0afd357611f8d078a1"
                    },
                    {
                        "humidity": 60,
                        "temperature": 20,
                        "date": "2019-01-12T22:49:47.041Z",
                        "_id": "5c3a6f0bfd357611f8d078a2"
                    }
                ]
            },
******************************************************
 // this whole object should not be returned
            {
              "stationName": "office",
                "measures": [] 
            }
******************************************************
        ]
    }

编辑 下面使用聚合的答案是可行的，但我仍然觉得奇怪，我需要这么多代码。如果在正常查询后，我得到与“.stations[0].measures”相同的结果，而不是整个聚合管道：

.then(stations => {     
    res.status(200).send(stations.stations[0].measures)
})

按照我阅读代码的方式，上述操作与：

const options = {'stations.$.measures': 1}

其中美元符号放入索引0，因为该索引是与查询部分匹配的站点的索引：stationName:“livingroom”

有人能解释一下吗？

运算符将查询结果中数组字段的内容限制为仅包含与$elemMatch条件匹配的第一个元素

在选择查询中尝试$elemMatch，如下所示：

const query = {
     apiKey: user.apiKey,
     'stations.stationName': req.params.stationName
}
const options = {
   'stations' : {$elemMatch: { 'stationName' : req.params.stationName }}
}

---

这并不是用

mongoose

来描述的，但这将在一个或多个文档中的站点数组中找到特定的站点名称，并仅返回

度量值

数组：

db.foo.aggregate([
// First, find the docs we are looking for:
{$match: {"stations.stationName": "livingroom"}}

// Got the doc; now need to fish out ONLY the desired station.  The filter will
// will return an array so use arrayElemAt 0 to extract the object at offset 0.
// Call this intermediate qqq:
,{$project: { qqq:
      {$arrayElemAt: [
          { $filter: {
            input: "$stations",
            as: "z",
            cond: { $eq: [ "$$z.stationName", "livingroom" ] }
      }}, 0]
      } 
}}

// Lastly, just project measures and not _id from this object:
,{$project: { _id:0, measures: "$qqq.measures" }}
                  ]);

---

那么您只想要至少存在一个度量值的站点？不，我只想要度量值数组的内容，来自我在查询中查找的站点：const query={apiKey:user.apiKey，'stations.stationName'：req.params.stationName}它应该只返回“livingroom”的度量值，但它也显示了电台“办公室”，正如你在上面的结果中所看到的。有什么想法吗？谢谢你的回答！我会试试这个，但它仍然不会只选择和返回度量值数组，对吗？是的，试试看！根据您对该问题的评论，它将返回所请求的stationName的度量值（预期结果）。这是第一个实际使用本机mongoose函数的答案。你能告诉我为什么在我做的例子中投影不起作用吗？您的方法工作得更好，因为它只返回所需的数据，但我上面的问题是，它还返回站点dat的度量值数组，而在de查询中，该数组与de station name不匹配。再次感谢！