Mongodb聚合查找记录限制

Question

我的moongose + mongodb中有这个功能：

   Blog.aggregate([{
                "$match": {"user_id": userblog}},
                {
                "$lookup": {
                    from: "comments", // collection name in db
                    localField: "_id",
                    foreignField: "blogid",
                    as: "comments"
                },                  
            }]).exec(function(err, docs) {


            });

这完美无缺，但我怎样才能限制评论并追溯最近10条记录？非常感谢。马可。

Answer 1

为您的代码添加限制

Blog.aggregate([{
        "$match": {"user_id": userblog}},
        {
        "$lookup": {
            from: "comments", // collection name in db
            localField: "_id",
            foreignField: "blogid",
            as: "comments"
        }
    }]).limit(10).exec(function(err, docs) {

    });

Answer 2

只需在聚合中添加限制：

Blog.aggregate([{
                "$match": {"user_id": userblog}},
                {
                "$lookup": {
                    from: "comments", // collection name in db
                    localField: "_id",
                    foreignField: "blogid",
                    as: "comments"
                }, 
                {
                    "$limit" : 10
                }                 
            }]).exec(function(err, docs) {


            });