多总和/在MongoDB的（和性别和总的结果）算

问题描述

我有这个文件：

{gender:"male", ...},
{gender:"male", ...},
{gender:"female", ...},
{gender:"female", ...},
{gender:"female", ...},

所以，我需要像retrive

So, i need retrive like

{
total:5,
male:2,
female:3
}

我的实际查询（没有工作）：

my actual query(no work):

db.collection.aggregate([
{
    $match:{...}
},
{
    $group:{
        _id:"$_id",
        gender:{
            $push:"$gender"
        },
        total:{
            $sum:1
        }
    }
},
{
    $unwind:"$gender"
},
{
    $group:{
        _id:"$gender",
        name:{
            $addToSet:"$all"
        },
        "count":{
            $sum:1
        }
    }
}
])

我怎么可以retrive性别和总的柜台？
谢谢

how i can retrive counter of gender and total?thanks

推荐答案

类似的东西会做的伎俩：

Something like that will do the trick:

db.collection.aggregate([
  {$project: {
    male: {$cond: [{$eq: ["$gender", "male"]}, 1, 0]},
    female: {$cond: [{$eq: ["$gender", "female"]}, 1, 0]},
  }},
  {$group: { _id: null, male: {$sum: "$male"},
                        female: {$sum: "$female"},
                        total: {$sum: 1},
  }},
])

生产给予你的例子：

Producing given your example:

{ "_id" : null, "male" : 2, "female" : 3, "total" : 5 }

的核心思想是利用href=\"http://docs.mongodb.org/manual/reference/operator/aggregation/cond/\" rel=\"nofollow\">条件前pression 映射性别为0或1。在此之后，你只需要在每个领域的简单相加。

The key idea is to use a conditional expression to map the gender to 0 or 1. After that, all you need is a simple sum over each field.

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