Mongo：分组、推送和排序

Question

我有一个 mongodb 收集数据，如下所示；我想按 EmployeedID（即 0001）分组，然后（按年龄）排序

{
"_id" : ObjectId("54d0512191a4da7736e9db43"),
"EmployeeID" : "0001",
"Speciality" : "xxx",
"Code" : "P",
"Age" : 8
}

/* 1 */
{
"_id" : ObjectId("54d0512191a4da7736e9db44"),
"EmployeeID" : "0002",
"Speciality" : "yyyyy",
"Code" : "P",
"Age" : 6
 }

/* 2 */
{
"_id" : ObjectId("54d0512191a4da7736e9db45"),
"EmployeeID" : "0001",
"Speciality" : "zzz",
 "Code" : "P",
 "Age" : 5
 }

我知道我可以使用以下方式进行分组。

collection.aggregate([
{$match:{"EmployeeId":0001}},
{$group:{"_id":"$EmployeeID",
        "speciality":{$push:"$Speciality"},
        "Code":{$push:"$Code"},
        "Age":{$push:"$Age"}}}
 ])

但是我如何在这里使用 $sort 呢？所以我的结果可能如下所示；

[{ "EmployeeID" : "0001",
"speciality" : [ "zzz","xxx"],
 "Code" :[ "P","P"],
 "Age" : [5,8]
 }]

Answer 1

您可以在分组阶段之前对文档进行排序：

collection.aggregate([
{$sort: {_id: -1}},
{$match:{"EmployeeId":0001}},
{$group:{"_id":"$EmployeeID",
    "speciality":{$push:"$Speciality"},
    "Code":{$push:"$Code"},
    "Age":{$push:"$Age"}}}
])

Answer 2

在处理大型集合时，在分组之前进行排序可能会超出 mongo 的内存。幸运的是，您可以将 allowDiskUse 设置为 true 以允许 mongo 写入临时文件。

Mongo：分组、推送和排序

Mongo: Group, push and sort

mongodb

node.js

aggregation-framework