mongo聚合-为字段的不同组的值累加 [英] mongo aggregation - accumulate for different groups of values of a field

问题描述

如果我有Player个格式的文件

{name: String, score: Int}

我有Group个文档，其中的组代表球员列表

and I have Group documents, where groups represent lists of players

{groupName: String, players: [ObjectID]}

玩家可以属于多个组.

我想对Player个文档进行汇总，并按Group分组(例如，使用一个汇总管道来获得每个组的球员得分总和).

I want to do an aggregation of Player documents, grouped by Group (ex. get the sums of players' scores for each group, with one aggregation pipeline).

我知道的选项:

=>给Player文档返回指向它们所关联的Group文档的指针，然后按GroupID返回$group.但我宁愿不必修改Player集合. (也许有一种方法可以在管道中将GroupID添加到文档中?)

=> give Player docs back pointers to Group documents they are a associated with, then $group by GroupID. But I prefer to not have to modify the Player collection. (perhaps there is a way to "add in" GroupIDs to the docs during the pipeline?)

=>为每个组单独呼叫，并使用$match阶段筛选仅要查询的当前组中的玩家.但是我更喜欢打一个简单的电话.

=> make a separate call for each group and use a $match stage to filter to just players in the current group being queried for. But I prefer to make a single, simple call.

如何实现这种汇总? MongoDB聚合是否具有某些功能?

How can I achieve such an aggregation? Does MongoDB Aggregation have something that works for this?

(顺便说一下，将组和玩家彼此映射到进行呼叫的内存中不是问题.因此，涉及将玩家列表作为参数传递的选项确实是公平的游戏.)

(By the way, it's not a problem to have the groups and players, mapped to each other, in memory where the call is being made. So options involving passing lists of players as arguments are indeed fair game.)

推荐答案

您可以使用

You could use the $lookup operator for this. Consider running the following aggregation pipeline:

Mongo shell:

db.group.aggregate([
    { "$unwind": "$players" },
    {
        "$lookup": {
            "from": "players",
            "localField": "players",
            "foreignField": "_id",
            "as": "players_join"
        }
    },
    { "$unwind": "$players_join" },
    {
        "$group": {
            "_id": {
                "groupName": "$groupName",
                "name": "$players_join.name"
            },
            "totalScore": { "$sum": "$players_join.score" }
        }
    }
])

您可以通过获取聚合框架包来添加对聚合的支持，该软件包为您包装了一些Mongo方法.只需流星添加 meteorhacks:aggregate ，您就可以开展业务.这将为您在Meteor中的集合添加一个汇总方法.

You can add support for aggregation by getting the aggregation framework package which wraps up some Mongo methods for you. Just meteor add meteorhacks:aggregate and you should be in business. This will add an aggregate method to your collections in Meteor.

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