我在聚合中遇到$ group阶段的问题。我想将所有“recentPlays.quiz”值组合在一起并计算重复值，因此我想从聚合中得到的最终结果是两个字段：测验对象和总计。在这种情况下，它将是：
{
"recentPlays" : [
{
"quiz" : {
"author" : "red-tester1",
"title" : "Asdffff Dfasdf"
},
"count": 1
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Creation Test 2"
},
"count": 1
},
{
"quiz" : {
"author" : "blue-tester1",
"title" : "Finky Fink"
},
"count": 4
}
]
}
这是我到目前为止的聚合：
db.users.aggregate([
{$match: { "recentPlays.date": {$gte:twentyFourHrsAgo}}},
{$project: {"recentPlays.quiz":1, _id:0}}
]).pretty();
这是聚合的输出：
MongoDB shell version: 3.2.1
connecting to: videoQuiz
{
"recentPlays" : [
{
"quiz" : {
"author" : "red-tester1",
"title" : "Asdffff Dfasdf"
}
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Creation Test 2"
}
},
{
"quiz" : {
"author" : "blue-tester1",
"title" : "Finky Fink"
}
},
{
"quiz" : {
"author" : "blue-tester1",
"title" : "Finky Fink"
}
},
{
"quiz" : {
"author" : "blue-tester1",
"title" : "Finky Fink"
}
},
{
"quiz" : {
"author" : "blue-tester1",
"title" : "Finky Fink"
}
}
]
}
以下是整个系列：
MongoDB shell version: 3.2.1
connecting to: videoQuiz
{
"_id" : ObjectId("580f7be62c6fd3c8065577f5"),
"user" : "blue-tester1",
"email" : "aslfjjcc@lkcjasdc.com",
"createdAt" : ISODate("2016-10-25T15:36:06.933Z"),
"recentPlays" : [
{
"quiz" : {
"author" : "red-tester1",
"title" : "Asdffff Dfasdf"
},
"score" : "0",
"date" : ISODate("2016-10-25T15:36:27.546Z")
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Creation Test 2"
},
"score" : "100",
"date" : ISODate("2016-10-25T15:37:09.142Z")
}
],
"mostRecentQuiz" : {
"author" : "red-tester3",
"title" : "Creation Test 2"
},
"mostRecentQuizTime" : ISODate("2016-10-25T15:37:09.142Z"),
"plays" : 2
}
{
"_id" : ObjectId("580a5dea650296d808082e65"),
"user" : "red-tester3",
"email" : "aldkdk@ccc.com",
"createdAt" : ISODate("2016-10-21T18:26:50.870Z"),
"recentPlays" : [
{
"quiz" : {
"author" : "red-tester2",
"title" : "TOP PLAYED QUIZ - Today"
},
"score" : "0",
"date" : ISODate("2016-10-21T18:27:16.292Z")
},
{
"quiz" : {
"author" : "red-tester2",
"title" : "TOP LIKED QUIZ - TODAY"
},
"score" : "100",
"date" : ISODate("2016-10-21T18:27:32.788Z")
},
{
"quiz" : {
"author" : "red-tester2",
"title" : "TOP LIKED QUIZ - TODAY"
},
"score" : "100",
"date" : ISODate("2016-10-21T18:27:44.497Z")
},
{
"quiz" : {
"author" : "Bertram",
"title" : "frfrf"
},
"score" : "100",
"date" : ISODate("2016-10-21T18:28:43.893Z")
},
{
"quiz" : {
"author" : "Bertram",
"title" : "Here We Go With the New Thing"
},
"score" : "0",
"date" : ISODate("2016-10-21T18:43:51.205Z")
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Presidents of the United States"
},
"score" : "0",
"date" : ISODate("2016-10-23T00:53:29.167Z")
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Presidents of the United States"
},
"score" : "0",
"date" : ISODate("2016-10-23T00:53:44.815Z")
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Creation Test 1"
},
"score" : "100",
"date" : ISODate("2016-10-23T23:50:55.355Z")
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Creation Test 2"
},
"score" : "100",
"date" : ISODate("2016-10-23T23:52:33.210Z")
},
{
"quiz" : {
"author" : "red-tester3",
"title" : "Here Is a New Title"
},
"score" : "100",
"date" : ISODate("2016-10-23T23:58:53.683Z")
}
],
"mostRecentQuiz" : {
"author" : "red-tester3",
"title" : "Here Is a New Title"
},
"mostRecentQuizTime" : ISODate("2016-10-23T23:58:53.683Z"),
"plays" : 10,
"likedQuizzes" : [
{
"title" : "TOP LIKED QUIZ - TODAY",
"author" : "red-tester2",
"date" : ISODate("2016-10-21T18:27:34.893Z")
},
{
"title" : "frfrf",
"author" : "Bertram",
"date" : ISODate("2016-10-21T18:28:45.863Z")
},
{
"title" : "Here We Go With the New Thing",
"author" : "Bertram",
"date" : ISODate("2016-10-21T18:43:53.148Z")
}
],
"createdQuizzes" : [
{
"title" : "Yeah Here We Go",
"id" : ObjectId("580a63f274b9a89c061f973e")
},
{
"title" : "Z Alpha",
"id" : ObjectId("580a641474b9a89c061f973f")
},
{
"title" : "Tags Limit Test",
"id" : ObjectId("580a6bda8d8049ac0bc1df2e")
},
{
"title" : "Tags Limit test2",
"id" : ObjectId("580a6bf98d8049ac0bc1df2f")
},
{
"title" : "Presidents of the United States",
"id" : ObjectId("580c09d28d8049ac0bc1df30")
},
{
"title" : "Creation Test 1",
"id" : ObjectId("580d4cca8d8049ac0bc1df31")
},
{
"title" : "Creation Test 2",
"id" : ObjectId("580d4d2d8d8049ac0bc1df32")
},
{
"title" : "Here Is a New Title",
"id" : ObjectId("580d4ead8d8049ac0bc1df33")
}
]
}
提前感谢任何指导。请原谅这些文件中的虚拟文本，仅供测试之用。
答案 0 :(得分：1)
这将是一个两步过程。第一步是$unwind＆＃34; recentPlays＆＃34;阵列。第二步是$group by＆＃34; recentPlays.quiz＆＃34;。
例如：
db.users.aggregate([
{ "$match" : { "recentPlays.date": { "$gte" : twentyFourHrsAgo}}},
{ "$project" : {"recentPlays.quiz":1, _id:0}},
{ "$unwind" : "$recentPlays" },
{ "$group" : { "_id" : "$recentPlays.quiz", "total" : { "$sum" : 1 } } }
]).pretty();