MongoDB 聚合与双卡答案

【问题标题】：MongoDB aggregate with dual sumMongoDB 聚合与双卡
【发布时间】：2013-05-02 00:05:39
【问题描述】：

我收集了一些移动设备，我想计算每个制造商的设备并计算每个型号。到目前为止，我所能得到的是：

{ $group : { 
  _id : "$hw.man", 
  mantotal : { $sum : 1 },
  models : { $addToSet : "$hw.mod" } 
} }

result:
[{"_id":"LGE","mantotal":1,"models":["GT540"]},{"_id":"asus","mantotal":1,"models":["Nexus 7"]},{"_id":"samsung","mantotal":3,"models":["GT-I9300","GT-I9200"]}]

或

{ $group : { 
  _id : { man : "$hw.man", mod : "$hw.mod" }, 
  total : { $sum : 1 } }
}

result:
[{"_id":{"man":"LGE","mod":"GT540"},"total":1},{"_id":{"man":"asus","mod":"Nexus 7"},"total":1},{"_id":{"man":"samsung","mod":"GT-I9300"},"total":2},{"_id":{"man":"samsung","mod":"GT-I9200"},"total":1}]

我怎样才能达到这样的结果：

{"_id":"samsung","mantotal":3,"models":[{mod: "GT-I9300", modtotal: 2}, {mod: "GT-I9200", modtotal: 1}]}

【问题讨论】：

标签： mongodb mongoose aggregation-framework

【解决方案1】：

假设您有一个代表手机的简单文档集合，其中列出了其制造商和型号，如下所示：

> db.phones.find({},{_id:0})
{ "man" : "LG", "mod" : "GT540" }
{ "man" : "LG", "mod" : "AB123" }
{ "man" : "Apple", "mod" : "iPhone4" }
{ "man" : "Apple", "mod" : "iPhone5" }
{ "man" : "Apple", "mod" : "iPhone5" }
{ "man" : "LG", "mod" : "GT540" }
{ "man" : "LG", "mod" : "GT540" }
{ "man" : "Samsung", "mod" : "Galaxy" }

以下是您如何多次分组以按制造商和型号获得总计和小计：

> gg1 =
{
 "$group" : {
    "_id" : {
        "ma" : "$man",
        "mo" : "$mod"
    },
    "subTotals" : {
        "$sum" : 1
    }
 }
}
> gg2 =
{
 "$group" : {
    "_id" : "$_id.ma",
    "total" : {
        "$sum" : "$subTotals"
    },
    "models" : {
        "$push" : {
            "mod" : "$_id.mo",
            "sub" : "$subTotals"
        }
    }
 }
}

> db.phones.aggregate(gg1, gg2)
{
"result" : [
    {
        "_id" : "LG",
        "total" : 4,
        "models" : [
            {
                "mod" : "AB123",
                "sub" : 1
            },
            {
                "mod" : "GT540",
                "sub" : 3
            }
        ]
    },
    {
        "_id" : "Apple",
        "total" : 3,
        "models" : [
            {
                "mod" : "iPhone5",
                "sub" : 2
            },
            {
                "mod" : "iPhone4",
                "sub" : 1
            }
        ]
    },
    {
        "_id" : "Samsung",
        "total" : 1,
        "models" : [
            {
                "mod" : "Galaxy",
                "sub" : 1
            }
        ]
    }
],
"ok" : 1
 }

【讨论】：