如何使用 mongodb 聚合和检索整个文档 [英] how to use mongodb aggregate and retrieve entire documents

问题描述

我对 mongodb 的聚合函数感到非常困惑.我只想在我的收藏中找到最新的文档.假设每条记录都有一个已创建"字段

I am seriously baffled by mongodb's aggregate function. All I want is to find the newest document in my collection. Let's say each record has a field "created"

db.collection.aggregate({
    $group: { 
        _id:0,
        'id':{$first:"$_id"},
        'max':{$max:"$created"}
    }
})

产生正确的结果，但我想要结果中的整个文档?我该怎么做?

yields the correct result, but I want the entire document in the result? How would I do that?

这是文档的结构:

{
    "_id" : ObjectId("52310da847cf343c8c000093"),
    "created" : 1389073358,
    "image" : ObjectId("52cb93dd47cf348786d63af2"),
    "images" : [
        ObjectId("52cb93dd47cf348786d63af2"),
        ObjectId("52f67c8447cf343509d63af2")
        ],
    "organization" : ObjectId("522949d347cf3402c3000001"),
    "published" : 1392601521,
    "status" : "PUBLISHED",
    "tags" : [ ],
    "updated" : 1392601521,
    "user_id" : ObjectId("52214ce847cf344902000000")
}

推荐答案

在文档中我发现 $$ROOT 表达式解决了这个问题.

In the documentation i found that the $$ROOT expression addresses this problem.

来自文档:http://docs.mongodb.org/手册/参考/操作员/聚合/组/#group-documents-by-author

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