在 mongodb 中与多个字段和 where 条件不同答案

【问题标题】：distinct with multiple fields and with where condition in mongodb在 mongodb 中与多个字段和 where 条件不同
【发布时间】：2014-05-31 22:20:37
【问题描述】：

我想在mongodb 中编写一个等效于distinct 和where 的查询。 sql查询是select DISTINCT key,score from GPC where note="test2" and notetwo = "meet2"

{ "_id" : ObjectId("4dc86fef6a0aa8513ab5f21c"), "key" : "SAGAR","score" : 16, "note" : "test1", "notetwo" : "meet1" } 
{ "_id" : ObjectId("4dc86ffd6a0aa8513ab5f21d"), "key" : "SAGAR456", "score" : 17, "note" : "testjh1", "notetwo" : "meetjh1" } 
{ "_id" : ObjectId("4dc8700b6a0aa8513ab5f21e"), "key" : "SAGAR33", "score" : 37, "note" : "test2", "notetwo" : "meet2" } 
{ "_id" : ObjectId("4dc871686a0aa8513ab5f21f"), "key" : "SAGAR33", "score" : 37, "note" : "test2", "notetwo" : "meet2" } 
{ "_id" : ObjectId("4dc871696a0aa8513ab5f220"), "key" : "SAGAR33", "score" : 37, "note" : "test2", "notetwo" : "meet2" } 
{ "_id" : ObjectId("4dc8716c6a0aa8513ab5f221"), "key" : "SAGAR456", "score" : 17, "note" : "testjh1", "notetwo" : "meetjh1" }

查询的预期结果是

[{"key" : "SAGAR33", "score" : 37}]

mongodb 中的等效查询是什么。我正在使用猫鼬来执行查询。

【问题讨论】：

标签： node.js mongodb mongoose

【解决方案1】：

您需要使用aggregate 查询来实现此目的。这是一个可以在 shell 中工作的例子（可以很容易地翻译成 Mongoose）：

db.gpc.aggregate([
    // your where clause: note="test2" and notetwo = "meet2"
    {"$match" : {note:"test2", notetwo:"meet2"}}, 
    // group by key, score to get distinct
    {"$group" : {_id : {key:"$key", score:"$score"}}}, 
    // Clean up the output
    {"$project" : {_id:0, key:"$_id.key", score:"$_id.score"}}
])

输出：

{ "result" : [ { "key" : "SAGAR33", "score" : 37 } ], "ok" : 1 }

【讨论】：