node.js - 根据 key 是否存在进行多个分组

我得到了带有以下示例数据的以下模型reportcharities：

    /* 1 */
{
    "_id" : ObjectId("5e1d79b93b591243962fa0c5"),
    "userId" : ObjectId("5dee2e536c3a72543518a0fa"),
    "charityId" : ObjectId("5dce381401a0171c50989d65"),
    "createdAt" : ISODate("2020-01-14T08:20:09.965Z"),
    "updatedAt" : ISODate("2020-01-14T08:20:09.965Z"),
    "__v" : 0
}

/* 2 */
{
    "_id" : ObjectId("5e1d7afd3b591243962fa0c6"),
    "userId" : ObjectId("5dee2e536c3a72543518a0fa"),
    "eventId" : ObjectId("5df1ea1efe164a3c9ef854df"),
    "createdAt" : ISODate("2020-01-14T08:25:33.169Z"),
    "updatedAt" : ISODate("2020-01-14T08:25:33.169Z"),
    "__v" : 0
}

/* 3 */
{
    "_id" : ObjectId("5e1d7b2c3b591243962fa0c7"),
    "userId" : ObjectId("5dee2e536c3a72543518a0fa"),
    "projectId" : ObjectId("5df73c88bc67dc3b60a542fc"),
    "createdAt" : ISODate("2020-01-14T08:26:20.551Z"),
    "updatedAt" : ISODate("2020-01-14T08:26:20.551Z"),
    "__v" : 0
}

/* 4 */
{
    "_id" : ObjectId("5e1dad44121cc1481303fb4d"),
    "userId" : ObjectId("5e1d8c4d3b591243962fa0d0"),
    "eventId" : ObjectId("5e1d8bdd3b591243962fa0cf"),
    "createdAt" : ISODate("2020-01-14T12:00:04.231Z"),
    "updatedAt" : ISODate("2020-01-14T12:00:04.231Z"),
    "__v" : 0
}

/* 5 */
{
    "_id" : ObjectId("5e1dad7c121cc1481303fb4e"),
    "userId" : ObjectId("5e1d8c4d3b591243962fa0d0"),
    "eventId" : ObjectId("5e1d8bdd3b591243962fa0cf"),
    "createdAt" : ISODate("2020-01-14T12:01:00.322Z"),
    "updatedAt" : ISODate("2020-01-14T12:01:00.322Z"),
    "__v" : 0
}

/* 6 */
{
    "_id" : ObjectId("5e1dad8b121cc1481303fb4f"),
    "userId" : ObjectId("5e1d8c4d3b591243962fa0d0"),
    "eventId" : ObjectId("5e1d8bdd3b591243962fa0cf"),
    "createdAt" : ISODate("2020-01-14T12:01:15.181Z"),
    "updatedAt" : ISODate("2020-01-14T12:01:15.181Z"),
    "__v" : 0
}

/* 7 */
{
    "_id" : ObjectId("5e1dada9121cc1481303fb50"),
    "userId" : ObjectId("5e1d8c4d3b591243962fa0d0"),
    "eventId" : ObjectId("5e1d8bdd3b591243962fa0cf"),
    "createdAt" : ISODate("2020-01-14T12:01:45.433Z"),
    "updatedAt" : ISODate("2020-01-14T12:01:45.433Z"),
    "__v" : 0
}

/* 8 */
{
    "_id" : ObjectId("5e1eb08ecaa8076b22547abc"),
    "userId" : ObjectId("5e1e9d5744b39654f05ed8b4"),
    "eventId" : ObjectId("5e1d8bdd3b591243962fa0cf"),
    "createdAt" : ISODate("2020-01-15T06:26:22.999Z"),
    "updatedAt" : ISODate("2020-01-15T06:26:22.999Z"),
    "__v" : 0
}

在这里，作为userId的用户可以一次将慈善组织报告为charityId，将项目报告为projectId或将事件报告为eventId。

现在，我需要按组查找每个类别的计数，并将其计数作为用户的总报告数。例如，对于这些“类型”中的每一个，我想得到以下计数：

  "eventId" : ObjectId("5e1d8bdd3b591243962fa0cf"), count: 5
 "projectId" : ObjectId("5df73c88bc67dc3b60a542fc"), count: 1
 "charityId" : ObjectId("5dce381401a0171c50989d65") count: 1
"eventId" : ObjectId("5df1ea1efe164a3c9ef854df") count: 1

...等等

文档中仅存在charityId，projectId或eventId之一，我无法在聚合中实现多个分组。

最佳答案

您需要使用以下聚合来重新构建数据：

db.collection.aggregate([
    {
        "$addFields": {
            "data": {
                "$filter": {
                    "input": {
                        "$objectToArray": "$$ROOT"
                    },
                    "as": "datum",
                    "cond": {
                        "$in": [
                            "$$datum.k",
                            [
                                "eventId",
                                "projectId",
                                "charityId"
                            ]
                        ]
                    }
                }
            }
        }
    },
    {
        "$unwind": "$data"
    },
    {
        "$group": {
            "_id": {
                "key": "$data.k",
                "value": "$data.v"
            },
            "count": {
                "$sum": 1.0
            }
        }
    },
    {
        "$project": {
            "type": "$_id.key",
            "count": "$count",
            "_id": "$_id.value"
        }
    }
]);

将为您提供以下输出：

{
    "type" : "projectId",
    "count" : 1.0,
    "_id" : ObjectId("5df73c88bc67dc3b60a542fc")
}
{
    "type" : "eventId",
    "count" : 1.0,
    "_id" : ObjectId("5df1ea1efe164a3c9ef854df")
}
{
    "type" : "charityId",
    "count" : 1.0,
    "_id" : ObjectId("5dce381401a0171c50989d65")
}
{
    "type" : "eventId",
    "count" : 5.0,
    "_id" : ObjectId("5e1d8bdd3b591243962fa0cf")
}

关于node.js - 根据 key 是否存在进行多个分组，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/59878008/