javascript - MongoDB 的映射缩减

Question

我有一个集合，其中每个对象都包含用户的详细信息以及用户对特定产品给出的评论，如下所示

{
"_id" : ObjectId("51efcbc8786df13540e46887"),
"value": {
    "UserDetails" : [
                        [
                            {
                                "country" : "CA",
                                "gender" : "M",
                                "age" : "18",
                                "userIdtemp" : ObjectId("51efcbc8786df13540e46887")
                            }
                        ]
                    ],
    "comments" :    [
                        {
                            "commentId" : ObjectId("51efcc41786df13540e46891"),
                            "comment" : "Hey, what's up?",
                            "created" : ISODate("2013-07-24T12:44:49.400Z"),
                            "productId" : ObjectId("51efcbd4786df13540e4688c"),
                            "userId" : ObjectId("51efcbc8786df13540e46887")
                        },
                        {
                            "commentId" : ObjectId("51efcc43786df13540e46893"),
                            "comment" : "Cool",
                            "created" : ISODate("2013-07-24T12:44:51.004Z"),
                            "productId" : ObjectId("51efcbd2786df13540e4688b"),
                            "userId" : ObjectId("51efcbc8786df13540e46887")
                        }
                    ]
    }
}
{
"_id" : ObjectId("51efcbc8786df13540e46888"),
"value" : {
     "UserDetails" : [
                        [
                            {
                               "country" : "US",
                               "gender" : "M",
                               "age" : "25",
                               "userIdtemp" : ObjectId("51efcbc8786df13540e46888")
                            }
                        ]
                ],
     "comments" : [
                    {
                        "commentId" : ObjectId("51efcc41786df13540e46892"),
                        "comment" : "Not much",
                        "created" : ISODate("2013-07-24T12:44:49.475Z"),
                        "productId" : ObjectId("51efcbd4786df13540e4688c"),
                        "userId" : ObjectId("51efcbc8786df13540e46888")
                    }
                ]
}
}
{
    "_id" : ObjectId("51efcbc8786df13540e46889"),
    "value" : {
            "UserDetails" : [
                    {
                            "country" : "US",
                            "gender" : "F",
                            "age" : "13",
                            "userIdtemp" : ObjectId("51efcbc8786df13540e46889")
                    }
            ]
    }
}

我必须单独提取评论以及带有 key 作为 ProductId 的 userDetails，所以我编写了类似于以下内容的 map

mapCommentsFrom = function(){
if("comments" in this.value)
{
    for(var idx = 0;idx<this.value.comments.length;idx++){
        var key = this.value.comments[idx].productId;
        var value = [{
            commentId: this.value.comments[idx].commentId,
            comment:this.value.comments[idx].comment,
            created:this.value.comments[idx].created,
            productId:this.value.comments[idx].productId,
            userId:this.value.comments[idx].userId,
            country:this.value.UserDetails[0][0].country,
            gender:this.value.UserDetails[0][0].gender,
            age : this.value.UserDetails[0][0].age
        }]

    }
}
emit(key,value);
}

reduceFrom = function(k,values){
return values;
}

但是当评论数量超过一个时，我只能得到最后一条评论以及用户详细信息，而其他评论的键和值将为空。像这样的事情

{ "_id" : null, "value" : null }
{
    "_id" : ObjectId("51efcbd2786df13540e4688b"),
    "value" : [
            {
                    "length" : 2,
                    "commentId" : ObjectId("51efcc43786df13540e46893"),
                    "comment" : "Cool",
                    "created" : ISODate("2013-07-24T12:44:51.004Z"),
                    "productId" : ObjectId("51efcbd2786df13540e4688b"),
                    "userId" : ObjectId("51efcbc8786df13540e46887"),
                    "country" : "CA",
                    "gender" : "M",
                    "age" : "18"
            }
    ]
}
{
    "_id" : ObjectId("51efcbd4786df13540e4688c"),
    "value" : [
            {
                    "length" : 1,
                    "commentId" : ObjectId("51efcc41786df13540e46892"),
                    "comment" : "Not much",
                    "created" : ISODate("2013-07-24T12:44:49.475Z"),
                    "productId" : ObjectId("51efcbd4786df13540e4688c"),
                    "userId" : ObjectId("51efcbc8786df13540e46888"),
                    "country" : "US",
                    "gender" : "M",
                    "age" : "25"
            }
    ]
}

有人可以帮我解决我缺少的内容吗？

感谢您提前提供帮助

Answer 1

由于声誉问题，我无法添加评论。但是您是否考虑过使用聚合框架。

$unwind 运算符将非常轻松地返回子文档数组，并且比使用 map/reduce 更快。

我不确定它是否能完全满足您的要求，但可能会有所帮助。

看一下，http://docs.mongodb.org/manual/reference/aggregation/unwind/