mongodb aggregation $addToSet

上篇文章学习了$unwind,作用是用来拆分成多条数据的,今天学的$addToSet是将多条数据合并成一条.

我们看具体怎么使用

首先准备一批销售数据

{

"_id": 1,

"item": "abc",

"price": 10,

"quantity": 2,

"date": ISODate("2014-01-01T08:00:00Z")

}

{

"_id": 2,

"item": "jkl",

"price": 20,

"quantity": 1,

"date": ISODate("2014-02-03T09:00:00Z")

}

{

"_id": 3,

"item": "xyz",

"price": 5,

"quantity": 5,

"date": ISODate("2014-02-03T09:05:00Z")

}

{

"_id": 4,

"quantity": 10,

"date": ISODate("2014-02-15T08:00:00Z")

}

{

"_id": 5,

"date": ISODate("2014-02-15T09:12:00Z")

}

然后我们想要按每年的天数来统计item的数量

首先要使用日期函数dayOfYear和year来分组

然后用addToSet将多个item合并

db.sales.aggregate(

[

{

$group:

{

_id: { day: { $dayOfYear: "$date"},year: { $year: "$date" } },

itemsSold: { $addToSet: "$item" }

}

}

]

)

最终结果如下：

{ "_id" : { "day" : 46,"year" : 2014 },"itemsSold" : [ "xyz","abc" ] }

{ "_id" : { "day" : 34,"jkl" ] }

{ "_id" : { "day" : 1,"itemsSold" : [ "abc" ] }