使用Mongodb查询以获取最近X分钟的数据 [英] Query to get last X minutes data with Mongodb

问题描述

我从mongodb开始，正在尝试查询具有以下文档格式的数据库:

I'm beginning with mongodb, and I'm trying to query my db that have this document format:

{ "_id" : ObjectId("520b8b3f8bd94741bf006033"), "value" : 0.664, "timestamp" : ISODate("2013-08-14T13:48:35Z"), "cr" : ISODate("2013-08-14T13:50:55.834Z") }

我可以使用以下查询从日期时间获取最后一条记录:

I can get the last records from a datetime with this query:

> db.mycol.find({timestamp:{$gt: ISODate("2013-08-14T13:48:00Z")}}).sort({x:1});

但是我试图从18分钟前开始获取一个包含值字段和时间戳的集合，如何建立对此的查询? 谢谢大家的耐心...

But I'm trying to get a set with the value fields and timestamps from 18 minutes ago, how can I build a query for this? Thanks everybody for your patience...

推荐答案

在18分钟的时间里，这与MongoDB无关，而与JavaScript和mongo shell中可用的内容有关:

For the 18 minutes part, that's not really about MongoDB, but about JavaScript and what's available in the mongo shell:

query = {
    timestamp: { // 18 minutes ago (from now)
        $gt: new Date(ISODate().getTime() - 1000 * 60 * 18)
    }
}

可以在mongo shell中运行，但是将Mongo驱动程序用于其他语言的确会有所不同.

Works in the mongo shell, but using Mongo drivers for other languages would be really different.

要投影"具有值和时间戳的较小模式:

To "project" over a smaller schema with both values and timestamps:

projection = {
    _id: 0,
    value: 1,
    timestamp: 1,
}

同时应用:

db.mycol.find(query, projection).sort({timestamp: 1});

嗯，那仍然不是一个集合"，因为可能有重复项.要摆脱它们，您可以使用聚合框架中的$group:

Well, that's still not a "set" since there might be duplicates. To get rid of them you can use the $group from the aggregation framework:

db.mycol.aggregate([
    {$match: query},
    {$group: {
        _id: {
            value: "$value",
            timestamp: "$timestamp",
        }
    }},
    {$project: {
        value: "$_id.value",
        timestamp: "$_id.timestamp",
    }},
    {$sort: {timestamp: 1}},
])

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