Question

我正在使用mongoDB，我有一个具有这种结构的集合：

{
 "_id" : 1,
 "State": "Vermont",
 "Temperature" : 20,
 "Day" : 1
}
{
 "_id" : 2,
 "State": "Vermont",
 "Temperature" : 50,
 "Day" : 2
}
{
 "_id" : 1,
 "State": "Vermont",
 "Temperature" : 40,
 "Day" : 2
}
{
 "_id" : 4,
 "State": "Texas",
 "Temperature" : 20,
 "Day" : 1
}
{
 "_id" : 5,
 "State": "Texas",
 "Temperature" : 50,
 "Day" : 2
}
{
 "_id" : 6,
 "State": "Texas",
 "Temperature" : 40,
 "Day" : 2
}

我需要在Node.js中过滤具有高温状态的文档，并仅使用最高温度更新文档添加密钥：值"Max_Value": "true"，结果将是：

{
 "_id" : 1,
 "State": "Vermont",
 "Temperature" : 20,
 "Day" : 1
}
{
 "_id" : 2,
 "State": "Vermont",
 "Temperature" : 50,
 "Day" : 2,
 "Max_Value": "true"
}
{
 "_id" : 1,
 "State": "Vermont",
 "Temperature" : 40,
 "Day" : 2
}
{
 "_id" : 4,
 "State": "Texas",
 "Temperature" : 20,
 "Day" : 1
}
{
 "_id" : 5,
 "State": "Texas",
 "Temperature" : 50,
 "Day" : 2,
 "Max_Value": "true"
}
{
 "_id" : 6,
 "State": "Texas",
 "Temperature" : 40,
 "Day" : 2
}

我的节点代码：

var MongoClient = require('mongodb').MongoClient;

MongoClient.connect('mongodb://localhost:27017/weather', function(err, db) {
    if(err) throw err;


    var options = {
        "sort": [['State','1'], ['Temperature','-1']]
    }

    db.collection('data').find({}, options).toArray(function(err, doc) {
        if(err) throw err;

        //Here I sorted the collection, but how I take only the first documents for each state?



        return db.close();
    });
});

那么，我如何只为每个州采用第一批文件并进行更新？

Answer 1

好像你没有并发麻烦。所以我尝试按照要求获取所有ID并逐个更新它们。

db.collection.aggregate([ {
    $sort : {
        "$Temperature" : -1
    }
}, {
    $group : {
        _id : "$State",
        myId : {
            $first : "$_id"
        }
    }
} ]).forEach(function(doc) {
    db.collection.update({
        _id : doc.myId
    }, {
        $set : {
            "Max_Value" : "true"
        }
    });
});

啊，你必须根据你的语言环境进行翻译。：）

Answer 2

最后我在Node.js上做了一些帮助，讨论了Mongo大学：

var MongoClient = require('mongodb').MongoClient;

MongoClient.connect('mongodb://localhost:27017/weather', function(err, db) {
    if(err){
    console.log(err.message);
    return db.close();
}

//filter the data
db.collection("data").find({},{},{ 'sort':[[ 'State',1 ], ['Temperature',-1]]}).toArray(function(err,docs){
    if(err) throw err ;

    var new_state = "";

    //do the forEach()
    docs.forEach(function(doc){

        //if State is not equeal that I have saved, so It's the first state with the maximun temperature
        if(new_state !== doc.State){
            new_state = doc.State;
            var query = { '_id' : doc._id};
            var operator = { '$set' : { 'month_high' : true}};
            var options = { 'multi' : true};

            //update the value
            db.collection("data").update(query,operator,options,function(err,data){
                if(err){
                    console.log(err.message);
                    //return db.close(); removed becouse the conection canceling
                }
                console.log("Success");
                return db.close();

            });
        }

    })

});

});

为每个州选择Top

2 个答案: