mongodb按多个字段分组值

例如，我有以下文件：

{
  "addr": "address1",
  "book": "book1"
},
{
  "addr": "address2",
  "book": "book1"
},
{
  "addr": "address1",
  "book": "book5"
},
{
  "addr": "address3",
  "book": "book9"
},
{
  "addr": "address2",
  "book": "book5"
},
{
  "addr": "address2",
  "book": "book1"
},
{
  "addr": "address1",
  "book": "book1"
},
{
  "addr": "address15",
  "book": "book1"
},
{
  "addr": "address9",
  "book": "book99"
},
{
  "addr": "address90",
  "book": "book33"
},
{
  "addr": "address4",
  "book": "book3"
},
{
  "addr": "address5",
  "book": "book1"
},
{
  "addr": "address77",
  "book": "book11"
},
{
  "addr": "address1",
  "book": "book1"
}

---

等等。


我怎样才能提出请求，哪个将描述前N个地址和每个地址前M本书？

预期结果示例：

地址1 |书1:5
|书2:10
|书3:50
|总计：65
|书2:10

|总计：M*10
…
| uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
地址n | book_u1:20
| book_u2:20
| book_um:20
|总计：M*20，使用如下聚合函数：

[
{$group: {_id : {book : '$book',address:'$addr'}, total:{$sum :1}}},
{$project : {book : '$_id.book', address : '$_id.address', total : '$total', _id : 0}}
]

它将为您提供如下结果：

        {
            "total" : 1,
            "book" : "book33",
            "address" : "address90"
        }, 
        {
            "total" : 1,
            "book" : "book5",
            "address" : "address1"
        }, 
        {
            "total" : 1,
            "book" : "book99",
            "address" : "address9"
        }, 
        {
            "total" : 1,
            "book" : "book1",
            "address" : "address5"
        }, 
        {
            "total" : 1,
            "book" : "book5",
            "address" : "address2"
        }, 
        {
            "total" : 1,
            "book" : "book3",
            "address" : "address4"
        }, 
        {
            "total" : 1,
            "book" : "book11",
            "address" : "address77"
        }, 
        {
            "total" : 1,
            "book" : "book9",
            "address" : "address3"
        }, 
        {
            "total" : 1,
            "book" : "book1",
            "address" : "address15"
        }, 
        {
            "total" : 2,
            "book" : "book1",
            "address" : "address2"
        }, 
        {
            "total" : 3,
            "book" : "book1",
            "address" : "address1"
        }

我没有完全了解您的预期结果格式，因此请随意将其修改为您需要的格式。

TLDR Summary 在现代MongoDB版本中，您可以使用基本聚合结果来强制执行此操作。对于“大”结果，请对每个分组运行并行查询（答案末尾有一个演示列表），或者等待解析，这将允许对

$push

到数组的项数进行“限制”

db.books.aggregate([
{“$组”：{
“_id”：{
“地址”：“$addr”，
“书”：“$book”
},
“簿记”：{“$sum”：1}
}},
{“$组”：{
“\u id”：“$\u id.addr”，
“书籍”：{
“$push”：{
“书”：“$\u id.book”，
“计数”：“$bookCount”
},
},
“计数”：{“$sum”：“$bookCount”}
}},
{“$sort”：{“count”：-1}，
{“$limit”：2}，
{“$project”：{
“图书”：{“$slice”：[“$books”，2]}，
“计数”：1
}}
])

---

MongoDB 3.6预览版 仍然没有解析，但在此版本中允许一个新的“非相关”选项，该选项将

“管道”

表达式作为参数，而不是

“localFields”

和

“foreignFields”

选项。然后，这允许与另一个管道表达式进行“自连接”，我们可以在其中应用，以返回“top-n”结果

db.books.aggregate([
{“$组”：{
“_id”：“$addr”，
“计数”：{“$sum”：1}
}},
{“$sort”：{“count”：-1}，
{“$limit”：2}，
{“$lookup”：{
“来自”：“书籍”，
“让”：{
“地址”：“$\u id”
},
“管道”：[
{“$match”：{
“$expr”：{“$eq”：[“$addr”，“$$addr”]}
}},
{“$组”：{
“_id”：“$book”，
“计数”：{“$sum”：1}
}},
{“$sort”：{“count”：-1}，
{“$limit”：2}
],
“作为”：“书籍”
}}
])

这里的另一个新增功能当然是通过

$expr

插入变量，用于选择“连接”中的匹配项，但一般前提是“管道中的管道”，其中内部内容可以通过父级的匹配项进行过滤。由于它们本身都是“管道”，我们可以分别得出各自的结果

这将是运行并行查询的下一个最佳选项，如果允许并能够在“子管道”处理中使用索引，实际上会更好。因此，它没有像引用的问题所要求的那样使用“限制到

$push

”，它实际上提供了一些应该更好的功能

---

原始内容 你似乎偶然发现了最重要的“N”问题。在某种程度上，您的问题相当容易解决，但没有您要求的确切限制：

db.books.aggregate([
{“$组”：{
“_id”：{
“地址”：“$addr”，
“书”：“$book”
},
“簿记”：{“$sum”：1}
}},
{“$组”：{
“\u id”：“$\u id.addr”，
“书籍”：{
“$push”：{
“书”：“$\u id.book”，
“计数”：“$bookCount”
},
},
“计数”：{“$sum”：“$bookCount”}
}},
{“$sort”：{“count”：-1}，
{“$limit”：2}
])

现在，这将给你一个这样的结果：

{
“结果”：[
{
“_id”：“地址1”，
“书籍”：[
{
“书”：“书4”，
“计数”：1
},
{
“书”：“书5”，
“计数”：1
},
{
“书”：“书1”，
“计数”：3
}
],
“计数”：5
},
{
“_id”：“地址2”，
“书籍”：[
{
“书”：“书5”，
“计数”：1
},
{
“书”：“书1”，
“计数”：2
}
],
“计数”：3
}
],
“好”：1
}

因此，这与您要求的不同之处在于，虽然我们确实获得了地址值的最高结果，但基本的“books”选择并不局限于所需的结果数量

这很难做到，但可以做到，尽管复杂性随着需要匹配的项目数量的增加而增加。为了保持简单，我们最多可以保持2个匹配：

db.books.aggregate([
{“$组”：{
“_id”：{
“地址”：“$addr”，
“书”：“$book”
},
“簿记”：{“$sum”：1}
}},
{“$组”：{
“\u id”：“$\u id.addr”，
“书籍”：{
“$push”：{
“书”：“$\u id.book”，
“计数”：“$bookCount”
db.books.aggregate([
    {
        $group: {
            _id: { addresses: "$addr", books: "$book" },
            num: { $sum :1 }
        }
    },
    {
        $group: {
            _id: "$_id.addresses",
            bookCounts: { $push: { bookName: "$_id.books",count: "$num" } }
        }
    },
    {
        $project: {
            _id: 1,
            bookCounts:1,
            "totalBookAtAddress": {
                "$sum": "$bookCounts.count"
            }
        }
    }

]) 

/* 1 */
{
    "_id" : "address4",
    "bookCounts" : [
        {
            "bookName" : "book3",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
},

/* 2 */
{
    "_id" : "address90",
    "bookCounts" : [
        {
            "bookName" : "book33",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
},

/* 3 */
{
    "_id" : "address15",
    "bookCounts" : [
        {
            "bookName" : "book1",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
},

/* 4 */
{
    "_id" : "address3",
    "bookCounts" : [
        {
            "bookName" : "book9",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
},

/* 5 */
{
    "_id" : "address5",
    "bookCounts" : [
        {
            "bookName" : "book1",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
},

/* 6 */
{
    "_id" : "address1",
    "bookCounts" : [
        {
            "bookName" : "book1",
            "count" : 3
        },
        {
            "bookName" : "book5",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 4
},

/* 7 */
{
    "_id" : "address2",
    "bookCounts" : [
        {
            "bookName" : "book1",
            "count" : 2
        },
        {
            "bookName" : "book5",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 3
},

/* 8 */
{
    "_id" : "address77",
    "bookCounts" : [
        {
            "bookName" : "book11",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
},

/* 9 */
{
    "_id" : "address9",
    "bookCounts" : [
        {
            "bookName" : "book99",
            "count" : 1
        }
    ],
    "totalBookAtAddress" : 1
}