MongoDb如何按月和年汇总 [英] MongoDb How to aggregate by month and year

问题描述

我是mongodb的新手，正在尝试学习Mongodb查询

I am new to mongodb and trying to learn Mongodb queries

    {
    "_id" : ObjectId("59815d4704ca1760a45957ca"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 200,
    "expenseRemark" : "aa",
    "expenseCategory" : "billing",
    "entryTime" : ISODate("2017-08-02T05:03:57Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("59815d5404ca1760a45957cb"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 300,
    "expenseRemark" : "ff",
    "expenseCategory" : "transport",
    "entryTime" : ISODate("2017-08-02T05:04:11Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("5980191d04ca1760a45957cd"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 100,
    "expenseRemark" : "rr",
    "expenseCategory" : "billing",
    "entryTime" : ISODate("2017-08-01T06:00:46Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("5980192604ca1760a45957ce"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 200,
    "expenseRemark" : "qq",
    "expenseCategory" : "transport",
    "entryTime" : ISODate("2017-08-01T06:01:03Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("5980192e04ca1760a45957cf"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 470,
    "expenseRemark" : "ff",
    "expenseCategory" : "transport",
    "entryTime" : ISODate("2017-08-01T06:01:11Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("59816ac004ca1760a45957d0"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 500,
    "expenseRemark" : "raj",
    "expenseCategory" : "transport",
    "entryTime" : ISODate("2017-08-02T06:01:26Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("59816acb04ca1760a45957d1"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 100,
    "expenseRemark" : "pet",
    "expenseCategory" : "pets",
    "entryTime" : ISODate("2017-08-02T06:01:37Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("597d7a9c04ca1760a45957d2"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 500,
    "expenseRemark" : "gt",
    "expenseCategory" : "sports",
    "entryTime" : ISODate("2017-07-30T06:20:04Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("597d7aaa04ca1760a45957d3"),
    "userEmail" : "[e-mail]",
    "expenseAmount" : 560,
    "expenseRemark" : "mov",
    "expenseCategory" : "entertainment",
    "entryTime" : ISODate("2017-07-30T06:20:14Z"),
    "__v" : 0
}

我想获得按年+月+ 分组的费用金额. 我尝试过

I want to get expenseAmount grouped by Year + Month. I tried

`db.expenses.aggregate( 
       {$project : { 
              month : {$month : "$entryTime"}, 
              year : {$year :  "$entryTime"}
          }}, 
        {$group : { 
                _id : {month : "$month" ,year : "$year" },  
              total : {$sum : "$expenseAmount"} 
        }})`

哪个给

{ "_id" : { "month" : 7, "year" : 2017 }, "total" : 0 }

{ "_id" : { "month" : 8, "year" : 2017 }, "total" : 0 }

请指导我如何获取汇总结果. 我不知道该怎么做.

Please guide me how can I get aggregated result. I could not figure out the way to do that.

谢谢

推荐答案

在投影阶段您丢失了expenseAmount字段.只需添加它:

You have lost expenseAmount field during projection stage. Simply add it:

   {$project : { 
          month : {$month : "$entryTime"}, 
          year : {$year :  "$entryTime"},
          expenseAmount : 1
      }},

请注意，如果文档中不存在该字段，则 $sum 返回0.

Note that if field does not exist in document, then $sum returns 0.

还要注意，还有另一个聚合运算符可以按您的预期执行- $addFields .它向文档添加新字段，并保留输入文档中的所有现有字段.但是在这种情况下，您只需要ExpenseAmount字段

Also note that there is another aggregation operator which performs as you expected - $addFields. It adds new fields to document and preserves all existing fields from the input document. But in this case you need only expenseAmount field

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