如何在MongoDB中使用该集合？

We had this following query in our Node.JS

我们在Node.JS中有以下查询

mongo.connect('mongodb://XXX:[e-mail]:54289/XXXdb', function (err, db) {
    var collection = db.collection('chatmessages')
    var stream = collection.find().sort({ _id: -1 }).limit(20).stream();
    stream.on('data', function (chat) { 
        socket.emit('user message', chat.content, chat.dateCreated); 
    });
});

As you can see, the query is a collection of last 20 records entered. But then from this result we would like to do resort again to 1 in _id so in the list we will have ID 55 - 75 for instance (the order). So the last one always at the bottom.

如您所见,查询是输入的最后20条记录的集合。但是从这个结果我们想再次使用_id中的1,所以在列表中我们将得到ID 55 - 75(例如)。所以最后一个总是在底部。

How do we achieve this again?

我们如何再次实现这一目标?

2 个解决方案

#1

You need to use the Aggregation Framework.

您需要使用聚合框架。

mongo.connect('mongodb://XXX:[e-mail]:54289/XXXdb', function (err, db) {
    var collection = db.collection('chatmessages')
    var stream = collection.aggregate([
        { "$sort": { "_id": -1}}, 
        { "$limit": 20 }, 
        { "$sort": { "_id": 1 }}
    ]);
    stream.on('data', function (chat) { 
        socket.emit('user message', chat.content, chat.dateCreated); 
    });
});

#2

The simplest thing to do will be to reverse the order of records returned by the query. So, instead of getting a stream, convert the response to array and use reverse() function, to reverse the order of records in it, before sending it through the socket!

最简单的方法是颠倒查询返回的记录顺序。因此,在通过套接字发送之前,不是获取流,而是将响应转换为数组并使用reverse()函数来反转其中的记录顺序!

mongo.connect('mongodb://XXX:[e-mail]:54289/XXXdb', function (err, db) {

    var collection = db.collection('chatmessages')

    collection.find().sort({ _id: _1 }).limit(20).toArray(function(err, docs) {

        if (err) {
            // handle error
        }

        docs.reverse();  // <-- This will reverse the order of records returned!


        // Send the the array of records through socket.
        socket.emit('user message', docs)

    })
});