聚合查询从嵌套子文档中获取最新元素的计数

Posted 2023-03-10

【中文标题】聚合查询从嵌套子文档中获取最新元素的计数

【英文标题】：Aggregate Query geting count of most recent element from nest subdocuments

【发布时间】：2021-07-21 05:14:39

【问题描述】：

我有一个包含许多用户的 mongodb 数据库，我跟踪的子文档之一是文件上传及其通过审核过程的状态。每个文件上传最终都会有一个附件状态。我希望能够提取一些指标来获取每个上传文件的当前状态总数。我开始构建一个聚合查询，从每个上传的文件中提取最新的附件子文档状态并计算它们。

数据结构如下：

 "userName": "johnDoe",
 "email": "[e-mail]",
 "uploads" : [
                
                        "_id" : ObjectId("adh12451e0012ce9da0"),
                        "fileName" : "TestDoc.txt",
                        "fileType" : "text/plain",
                        "created" : ISODate("2021-01-06T15:26:14.166Z"),
                        "attachmentStatus" : [ ]
                ,
                
                        "_id" : ObjectId("5ff5d6c066cacc0012ed655a"),
                        "fileName" : "testerABC.txt",
                        "fileType" : "text/plain",
                        "created" : ISODate("2021-01-06T15:26:56.027Z"),
                        "attachmentStatus" : [
                                
                                        "_id" : ObjectId("60884f733f88bd00129b9ad4"),
                                        "status" : "Uploaded",
                                        "date" : ISODate("2021-04-22T02:23:00Z")
                                ,
                                
                                        "_id" : ObjectId("60884f733f88bd00129b9ad5"),
                                        "status" : "Processing",
                                        "date" : ISODate("2021-04-26T04:54:00Z")
                                
                        ]
                ,
                
                        "_id" : ObjectId("6075c82a19fdcc0012f81907"),
                        "fileName" : "Test file.docx",
                        "fileType" : "application/word",
                        "created" : ISODate("2021-04-13T16:34:50.955Z"),
                        "attachmentStatus" : [
                                
                                        "_id" : ObjectId("72844f733f88bd11479b9ad7"),
                                        "status" : "Uploaded",
                                        "date" : ISODate("2021-04-23T03:42:00Z")
                                ,
                                
                                        "_id" : ObjectId("724986d73f88bd00147c9wt8"),
                                        "status" : "Completed",
                                        "date" : ISODate("2021-04-24T01:37:00Z")
                                
                        ]
                
        ]

 "userName": "janeDoe",
 "email": "[e-mail]",
 "uploads" : [
                
                        "_id" : ObjectId("ej9784652h0012ce9da0"),
                        "fileName" : "myResume.txt",
                        "fileType" : "text/plain",
                        "created" : ISODate("2021-02-13T12:36:14.166Z"),
                        "attachmentStatus" : [
                                
                                        "_id" : ObjectId("15dhdf6f88bd00147c9wt8"),
                                        "status" : "Completed",
                                        "date" : ISODate("2021-04-24T01:37:00Z")
                                
                  ]
                , 

如何为每个上传的文件提取最新的附件状态，然后总结状态？

我想要这样的东西：

 "status" : "Completed", "Count" : 2 
 "status" : "Processing", "Count" : 1 
...

我非常接近这个聚合查询，但它会抓取每一个状态，而不仅仅是每个文件的单个最新状态。 （每个文件一个当前状态）。

db.myDB.aggregate([

  "$match" : 
    "uploads.attachmentStatus": 
      "$elemMatch":  "status":  "$exists": true  
      
    
,
 $unwind: "$uploads",
 $unwind: "$uploads.attachmentStatus",

  $sortByCount: "$uploads.attachmentStatus.status"
,

  $project: 
    _id:0,
    status: "$_id",
    Count: "$count"
  

]).pretty();

有什么建议吗？

【参考方案1】：

演示 - https://mongoplayground.net/p/zzOR9qhqny0

---

$sort: "uploads.attachmentStatus.date": -1 ,获取最新一期

$group: _id: "$uploads._id", status: $first: "$uploads.attachmentStatus.status" 按uploads._id对记录进行分组，取top状态（按日期排序后的最新状态）。

查询

 $sort:  "uploads.attachmentStatus.date": -1  ,
 $group:  _id: "$uploads._id", status:  $first: "$uploads.attachmentStatus.status"   ,

---

完成查询

db.collection.aggregate([
   $match:  "uploads.attachmentStatus":  "$elemMatch":   "status":  "$exists": true     ,
   $unwind: "$uploads" ,
   $unwind: "$uploads.attachmentStatus" ,
   $sort:  "uploads.attachmentStatus.date": -1  ,
   $group:  _id: "$uploads._id", status:  $first: "$uploads.attachmentStatus.status"   ,
   $sortByCount: "$status" ,
   $project:  _id: 0, status: "$_id", Count: "$count"  
])