在 Mongodb/pymongo 中按字符串长度排序 [英] sort by string length in Mongodb/pymongo

问题描述

我想知道是否有人知道如何按字符串长度对 mongodb find() 结果进行排序.

I was wondering if anyone knows how to sort a mongodb find() result by string length.

我尝试过类似 db.foo.find().sort({item.lenght:-1}) 但显然不起作用.有人可以帮助我并建议我在 pymongo 中做同样的事情吗?

I have tried something like db.foo.find().sort({item.lenght:-1}) but obviously doesn't work. Can somebody help me and also suggest me a way to do the same thing but in pymongo?

推荐答案

我个人喜欢在聚合框架中看到很多东西(和基本 API)，例如:

There are lot of things ( and basic API ) I would personally love to see in the aggregation framework such as:

• log(如对数)
• 细胞
• 地板

• 总和

• 长度

仅举几例.

这不是在ceil"和floor"等情况下使用 $mod 运算符或其他方式的模糊用法.但我离题了.

And that is without resorting to obscure usages of the $mod operator or other means in such cases as "ceil" and "floor". But I digress.

您的字符串长度"属于这一类.提出关于它的 JIRA 问题.但现在你可以使用 mapReduce 和现有的 JavaScript 功能:

Your "string length" falls into this category. Raise a JIRA issue about it. But for now you you can use mapReduce and the existing JavaScript functionality:

db.collection.mapReduce(
    function() {
        emit( this.item.length, this.item );
    },
    function(key,values) {
        return values;
    },
    { "out": { "inline": 1 } }
)

因此，虽然它确实具有mapReduce"时髦风格，即返回一个重新整形的文档，并且当然所有内容都匹配一个数组中的相同长度，但它所做的是利用mapReduce"的性质(不仅限于 MongoDB )并允许在响应中对发出的键"值进行排序.

So while that does actually have the "mapReduce" funky style of returning a re-shaped document and with of course everything matching the same length in an array, what it does do is take advantage of the nature of "mapReduce" ( not just restricted to MongoDB ) and allows the emitted "key" value to be sorted in the response.

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