node.js - 如何使用mongodb聚合以下数据

Question

我有一个集合名称为“sensors”的数据库，它看起来像这样:

{ "_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe3"), "type" : "thermometer", "value" : 23, "createdAt" : ISODate("2019-08-09T07:58:31.698Z"), "updatedAt" : ISODate("2019-08-09T07:58:31.698Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe4"), "type" : "hygrometer", "value" : 74, "createdAt" : ISODate("2019-08-09T07:58:31.739Z"), "updatedAt" : ISODate("2019-08-09T07:58:31.739Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"), "type" : "thermometer", "value" : 25, "createdAt" : ISODate("2019-08-09T07:58:32.551Z"), "updatedAt" : ISODate("2019-08-09T07:58:32.551Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"), "type" : "hygrometer", "value" : 86, "createdAt" : ISODate("2019-08-09T07:58:32.584Z"), "updatedAt" : ISODate("2019-08-09T07:58:32.584Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe7"), "type" : "thermometer", "value" : 20, "createdAt" : ISODate("2019-08-09T07:58:33.554Z"), "updatedAt" : ISODate("2019-08-09T07:58:33.554Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"), "type" : "hygrometer", "value" : 84, "createdAt" : ISODate("2019-08-09T07:58:33.587Z"), "updatedAt" : ISODate("2019-08-09T07:58:33.587Z"), "__v" : 0 }

我想要做的是查询最后两个文档，温度计和湿度计，然后检查每个文档的值。然后根据我使用 $match 标记设置的条件，我执行我想要的任何操作。

MongoClient.connect('mongodb://localhost', { useNewUrlParser: true }, function (err, client) {
  if (err) throw err;
  var db = client.db('mongodb');
    db.collection('sensors').aggregate(
     [
       { $sort: { _id: -1 } },
       { $limit: 1 },
       {
        $match: {"type": "hygrometer", "value": { "$gt": 60 } }
       }
     ]
   ).toArray(function(err, item) {
         if(err) console.log('error');
         if(item.length > 0) console.log('Dehumidifier ON');
         else console.log('Dehumidifier OFF');
});

这只是最后一个数据(湿度计)的实现，但我应该如何检查最后两个文档，然后对温度计执行单独的操作，例如“AC ON/OFF”？我在想以某种方式让它检查 item.type == "thermometer"何时执行某些操作，但 item.type 语法似乎不起作用。

Answer 1

请尝试这个:

查询 1:

db.getCollection('sensors').aggregate(
    [
        { $sort: { _id: -1 } }, { $group: { _id: '$type', data: { $push: '$$ROOT' } } },
        { $project: { type: '$_id', _id: 0, lastTwo: { $slice: ["$data", 2] } } },
        { $unwind: '$lastTwo' },
        {
            $match: { $or: [{ 'type': 'hygrometer' }, { "type": "thermometer", "lastTwo.value": { "$gt": 60 } }] }
        }
    ])

查询 2:

  //Check the response below & If you want to group again on type, adding `$group` stage to the above query.    

  db.getCollection('sensors').aggregate(
    [
        { $sort: { _id: -1 } }, { $group: { _id: '$type', data: { $push: '$$ROOT' } } },
        { $project: { type: '$_id', _id: 0, lastTwo: { $slice: ["$data", 2] } } },
        { $unwind: '$lastTwo' },
        {
            $match: { $or: [{ 'type': 'hygrometer' }, { "type": "thermometer", "lastTwo.value": { "$gt": 60 } }] }
        }, { $group: { _id: '$type', data: { $push: '$$ROOT' } } }, { $project: { type: '$_id', _id: 0, data: 1 } }
    ])

在Output 1中，您可以简单地检查特定类型的对象是否存在，并在Output 2中的代码中执行某些操作(Vs)，您必须检查类型和数据数组是否为空。

示例数据:

/* 1 */
{
    "_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe3"),
    "type" : "thermometer",
    "value" : 23,
    "createdAt" : ISODate("2019-08-09T07:58:31.698Z"),
    "updatedAt" : ISODate("2019-08-09T07:58:31.698Z"),
    "__v" : 0
}

/* 2 */
{
    "_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe4"),
    "type" : "hygrometer",
    "value" : 74,
    "createdAt" : ISODate("2019-08-09T07:58:31.739Z"),
    "updatedAt" : ISODate("2019-08-09T07:58:31.739Z"),
    "__v" : 0
}

/* 3 */
{
    "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"),
    "type" : "thermometer",
    "value" : 251,
    "createdAt" : ISODate("2019-08-09T07:58:32.551Z"),
    "updatedAt" : ISODate("2019-08-09T07:58:32.551Z"),
    "__v" : 0
}

/* 4 */
{
    "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"),
    "type" : "hygrometer",
    "value" : 86,
    "createdAt" : ISODate("2019-08-09T07:58:32.584Z"),
    "updatedAt" : ISODate("2019-08-09T07:58:32.584Z"),
    "__v" : 0
}

/* 5 */
{
    "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe7"),
    "type" : "thermometer",
    "value" : 20,
    "createdAt" : ISODate("2019-08-09T07:58:33.554Z"),
    "updatedAt" : ISODate("2019-08-09T07:58:33.554Z"),
    "__v" : 0
}

/* 6 */
{
    "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"),
    "type" : "hygrometer",
    "value" : 84,
    "createdAt" : ISODate("2019-08-09T07:58:33.587Z"),
    "updatedAt" : ISODate("2019-08-09T07:58:33.587Z"),
    "__v" : 0
}

输出 1:

/* 1 */
{
    "type" : "thermometer",
    "lastTwo" : {
        "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"),
        "type" : "thermometer",
        "value" : 251,
        "createdAt" : ISODate("2019-08-09T07:58:32.551Z"),
        "updatedAt" : ISODate("2019-08-09T07:58:32.551Z"),
        "__v" : 0
    }
}

/* 2 */
{
    "type" : "hygrometer",
    "lastTwo" : {
        "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"),
        "type" : "hygrometer",
        "value" : 84,
        "createdAt" : ISODate("2019-08-09T07:58:33.587Z"),
        "updatedAt" : ISODate("2019-08-09T07:58:33.587Z"),
        "__v" : 0
    }
}

/* 3 */
{
    "type" : "hygrometer",
    "lastTwo" : {
        "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"),
        "type" : "hygrometer",
        "value" : 86,
        "createdAt" : ISODate("2019-08-09T07:58:32.584Z"),
        "updatedAt" : ISODate("2019-08-09T07:58:32.584Z"),
        "__v" : 0
    }
}

输出 2:

/* 1 */
{
    "type" : "hygrometer",
    "data" : [ 
        {
            "type" : "hygrometer",
            "lastTwo" : {
                "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"),
                "type" : "hygrometer",
                "value" : 84,
                "createdAt" : ISODate("2019-08-09T07:58:33.587Z"),
                "updatedAt" : ISODate("2019-08-09T07:58:33.587Z"),
                "__v" : 0
            }
        }, 
        {
            "type" : "hygrometer",
            "lastTwo" : {
                "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"),
                "type" : "hygrometer",
                "value" : 86,
                "createdAt" : ISODate("2019-08-09T07:58:32.584Z"),
                "updatedAt" : ISODate("2019-08-09T07:58:32.584Z"),
                "__v" : 0
            }
        }
    ]
}

/* 2 */
{
    "type" : "thermometer",
    "data" : [ 
        {
            "type" : "thermometer",
            "lastTwo" : {
                "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"),
                "type" : "thermometer",
                "value" : 251,
                "createdAt" : ISODate("2019-08-09T07:58:32.551Z"),
                "updatedAt" : ISODate("2019-08-09T07:58:32.551Z"),
                "__v" : 0
            }
        }
    ]
}

根据评论进行更新(如果您需要任何类型的文档，因为文档总是有序的)，请尝试以下操作:

db.sensors.aggregate( [ { $sort: { _id: -1 } }, { $limit: 2 }, { $match: { $or: [{ 'type': 'hygrometer' , "value": { "$gt": 60 }}, { "type": "thermometer", "value": { "$gt": 20 } }] } } ] )

或将上述查询中的 $slice: ["$data", 2] 更改为 $slice: ["$data", 1]。