Mongodb聚合将书籍转换为作者数组答案

【问题标题】：Mongo DB aggregation to convert books to array of authorsMongodb聚合将书籍转换为作者数组
【发布时间】：2020-06-05 14:08:35
【问题描述】：

我的藏书是这样的：

{
    "book": {
        "title": "Book1",
        "author": "Tom"
    },
    "quantity": 3
},
{

    "book": {
        "title": "Book2",
        "author": "Tom"
    },
    "quantity": 4
},
{

    "book": {
        "title": "Book3",
        "author": "Dick"
    },
    "quantity": 9
},
{

    "book": {
        "title": "Book4",
        "author": "Harry"
    },
    "quantity": 6
},
{

    "book": {
        "title": "Book5",
        "author": "Chris"
    },
    "quantity": 7
},
{

    "book": {
        "title": "Book6",
        "author": "Dick"
    },
    "quantity": 10
}

此集合包含书名、作者和数量的书籍文档。

我需要帮助来进行聚合，该聚合将输出作者数组及其书籍和数量。示例 - Tom 创作了“Book1”和“Book2”，“Dick”创作了“Book6”和“Book3”。

authors: [
    {
        "name": "Tom",
        "books": [
            {
                    "title": "Book1",
                    "quantity": "3"
            },
            {
                    "title": "Book2",
                    "quantity": "4"
            }
        ]
    },
    {
        "name": "Dick",
        "books": [
            {
                    "title": "Book6",
                    "quantity": "10"
            },
            {
                    "title": "Book3",
                    "quantity": "9"
            }
        ]
    },
    {
        "name": "Harry",
        "books": [
            {
                    "title": "Book4",
                    "quantity": "6"
            }
        ]
    }
]

【问题讨论】：

标签： mongodb mongodb-query aggregation-framework

【解决方案1】：

尝试如下：

db.collection.aggregate([
    {
        $group: {
            _id: "$book.author",
            books: { $push: { "title": "$book.title", "quantity": "$quantity"} }
        },

    }
])

输出将是

/* 1 */
{
    "_id" : "Chris",
    "books" : [
        {
            "title" : "Book5",
            "quantity" : 7
        }
    ]
},

/* 2 */
{
    "_id" : "Harry",
    "books" : [
        {
            "title" : "Book4",
            "quantity" : 6
        }
    ]
},

/* 3 */
{
    "_id" : "Dick",
    "books" : [
        {
            "title" : "Book3",
            "quantity" : 9
        },
        {
            "title" : "Book6",
            "quantity" : 10
        }
    ]
},

/* 4 */
{
    "_id" : "Tom",
    "books" : [
        {
            "title" : "Book1",
            "quantity" : 3
        },
        {
            "title" : "Book2",
            "quantity" : 4
        }
    ]
}

【讨论】：

【解决方案2】：

试试这个聚合：

db.collection.aggregate([{
$group: {
  _id: "$book.author",
  books: {
    $push: {
      title: "$book.title",
      quantity: "$quantity"
    }
  }
}},{
$project: {
  "name": "$_id",
  "books": 1,
  "_id": 0
}}])

我在 mongo 操场上试过： https://mongoplayground.net/p/m-QbX-uzkkt

【讨论】：