MongoDB双$ group聚合

Question

我有几个文档看起来像这样:

{
        "_id" : ObjectId("50b59cd75bed76f46522c34e"),
        "player_id" : 0,
        "league_id" : 2,
        "results" : [
                {   "discipline" : "football",
                    "score" : 25.15
                },
                {
                        "discipline" : "basketball",
                        "score" : 21.24
                },
                {
                        "discipline" : "cycling",
                        "score" : 68.19
                },]
}

我尝试聚合这些数据.首先展开结果数组,然后只留下" 足球 "和" 骑自行车 ",接下来计算平均结果.这部分我做了,它正在发挥作用.我的代码:

db.grades.aggregate(
    {$unwind:"$results"},
    {$match: {$or: [{"results.discipline":"football"},{"results.discipline":"cycling"} ]}},
    {$group:{_id:{player_id:"$player_id",league_id:"$league_id"}, 'average':{$avg:"$results.score"}}},
    )

然后我尝试通过league_id聚合,这意味着,普通玩家在特定联赛中得出结果,添加到上面的代码: {$group:{_id:"$_id.league_id",aver_league:{$avg:$average}}}

现在代码看起来像:

db.grades.aggregate(
        {$unwind:"$results"},
        {$match: {$or: [{"results.discipline":"football"},{"results.discipline":"cycling"} ]}},
        {$group:{_id:{player_id:"$player_id",league_id:"$league_id"}, 'average':{$avg:"$results.score"}}},
{$group:{_id:"$_id.league_id",aver_league:{$avg:$average}}}
        )

控制台显示:出了JavaScript execution failed: ReferenceError: $average is not defined.什么问题？我在哪里弄错了？是否有可能聚合_id.league_id？

Answer 1

试试这个管道：

[
 {$unwind:"$results"}, 
 {$match: {"results.discipline":{$in:["football", "basketball"]}}}, 
 {$group{_id:{player_id:"$player_id",league_id:"$league_id"}, 'average':{$avg:"$results.score"}}} 
]

它对我和你的医生有用：

{
"result" : [
    {
        "_id" : {
            "player_id" : 0,
            "league_id" : 2
        },
        "average" : 23.195
    }
],
"ok" : 1
}

UPD。如果你想再次分组，可以通过league_id：

[{$unwind:"$results"}, 
{$match: {"results.discipline":{$in:["football", "basketball"]}}}, 
{$group:{_id:{player_id:"$player_id",league_id:"$league_id"}, 'average':{$avg:"$results.score"}  }}, 
{$group:{_id:"$_id.league_id", 'average':{$avg:"$average"}  }} ]

{ "result" : [ { "_id" : 2, "average" : 23.195 } ], "ok" : 1 }