在mongo聚合管道的投影阶段检查元素是否出现在数组中

Aidan Ewen 发表于 Dev

艾丹·埃文（Aidan Ewen）

我有一些mongo文件，例如-

{
    "_id" : "c959e4d6-961d-4043-ade6-2f93aa055e11",
    "events" : [
        "clickOut"
        "showHoverAd",
        "closeHoverAd"
    ]
}
{ 
    "_id" : "d0dcb2be-f8bc-45cd-8337-d89a16063b08", 
    "events" : [ 
        "zoom",
        "pan"
    ] 
}
{
    "_id" : "9179b26e-e45c-48ab-93f6-e73b8ebe559b",
    "events" : [
        "clickOut"
    ]
}
{
    "_id" : "db0b82ad-7a33-4ce8-9117-f6ecf041d0d9",
    "events" : [
        "adjustStars",
        "adjustPrice",
        "closeHoverAd",
        "showHoverAd"
    ]
}

我正在尝试在聚合管道中使用projection阶段来识别特定字符串是否出现在事件字段中。

db.events.aggreate([
    {$project: {
        session: '$_id',
        clickedOut: {
            $cond: [{$elemMatch: {'$events':'clickOut'}},true,false]
        }
    }}
])

我遇到错误- exception: invalid operator '$elemMatch'。

我希望输出文档看起来像-

{
    "session" : "c959e4d6-961d-4043-ade6-2f93aa055e11",
    "clickedOut" : false
}
{ 
    "session" : "d0dcb2be-f8bc-45cd-8337-d89a16063b08", 
    "clickedOut" : true
}

但是我似乎找不到解决方法。我尝试使用$in和$all或简单地

$cond: {'$events':'clickOut'}

但是我什么都没得到。

克列丹

使用以下聚合：

db.events.aggregate([
    {
        "$unwind": "$events"
    },
    {
        "$project": {
            "_id": 0,
            "session": "$_id",
            "clickedOut": {
                "$cond": [ { "$eq": [ "$events", "clickOut" ] }, 1, 0 ]
            }
        }
    },
    {
        "$group": {
            "_id": "$session",
            "count": {
                "$sum": "$clickedOut"
            }
        }
    },
    {
        "$project": {
            "_id": 0,
            "session": "$_id",
            "clickedOut": {
                "$cond": [ { "$eq": [ "$count", 1 ] }, true, false ]
            }            
        }
    },
]);

输出：

/* 1 */
{
    "result" : [ 
        {
            "session" : "db0b82ad-7a33-4ce8-9117-f6ecf041d0d9",
            "clickedOut" : false
        }, 
        {
            "session" : "9179b26e-e45c-48ab-93f6-e73b8ebe559b",
            "clickedOut" : true
        }, 
        {
            "session" : "d0dcb2be-f8bc-45cd-8337-d89a16063b08",
            "clickedOut" : false
        }, 
        {
            "session" : "c959e4d6-961d-4043-ade6-2f93aa055e11",
            "clickedOut" : true
        }
    ],
    "ok" : 1
}