Mongo DB +与最后一个字段的数据

我有collections中的示例json数据。

样本数据：

[{ "_id" : 1, "username" : "abcd", "createdDate" : ISODate("2016-06-03T08:52:32.434Z") }, { "_id" : 2, "username" : "abcd", "createdDate" : ISODate("2016-05-03T09:52:32.434Z") }, { "_id" : 3, "username" : "abcd", "createdDate" : ISODate("2016-04-03T10:52:32.434Z") }, { "_id" : 4, "username" : "xyz", "createdDate" : ISODate("2016-03-03T10:52:32.434Z") },{ "_id" : 5, "username" : "xyz", "createdDate" : ISODate("2016-02-03T10:52:32.434Z") },{ "_id" : 6, "username" : "zzz", "createdDate" : ISODate("2016-01-03T10:52:32.434Z") }] 

这些数据我需要检索以下条件的数据。

1. 按用户名分组。
2. 用户名不等于“zzz”
3. 按datesorting。
4. 需要date字段（最新/最后一个logging）。
5. 得到总数。

期待输出：

 [{ "username" : "abcd", "createdDate" : "2016-06-03T08:52:32.434Z", "total" : 3 }, { "username" : "xyz", "createdDate" : "2016-03-03T10:52:32.434Z", "total" : 2 }] 

查询：

 db.logs.aggregate([ { "$match": { "username": { "$ne": "zzz" } }}, { "$group": { "_id": { "username": "$username", "createdDate": "$createdDate" }, "count": { "$sum": 1 } }}]) 

Answer 1

尝试这个 ：

  db.logs.aggregate([ { "$match":{ "username":{ "$ne":"zzz" } } }, { "$group":{ _id:"$username", "count":{ "$sum":1 }, date:{ $max:"$createdDate" } } }, { $project:{ username:"$_id", total:"$count", createdDate:"$date" } } ]) 

产量

  { "_id":"xyz", "username":"xyz", "total":2, "createdDate": ISODate("2016-03-03T10:52:32.434 Z") }{ "_id":"abcd", "username":"abcd", "total":3, "createdDate": ISODate("2016-06-03T08:52:32.434 Z") }