Mongodb Mongo DB聚合将书籍转换为作者数组

我的藏书如下：

{
    "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
}

本藏书有书名、作者和数量的书籍文档

我想得到一些关于聚合的帮助，聚合可以输出作者的书籍和数量。例如，汤姆写了《第一本书》和《第二本书》，《迪克》写了《第六本书》和《第三本书》

请尝试以下操作：

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
        }
    ]
}

尝试此聚合：

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

我在mongo游乐场试过：

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