按Mongodb/pymongo中的字符串长度排序 [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.

我尝试了类似db.foo.find().sort({item.lenght:-1})的方法，但是显然不起作用.有人可以帮我，也可以建议我用pymongo做同样事情的方法吗?

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

我个人会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(以对数形式)
• ceil
• 地板

• 总和

• 长度

仅举几例.

并且在不使用 $mod 运算符或其他手段(例如天花板"和地板")的情况下，这是不可行的.但是我离题了.

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.提出有关此问题的JIRA问题.但是，现在您可以使用 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，尽管实际上确实具有返回重新整形的文档的"mapReduce"时髦风格，并且当然所有内容都与数组中的相同长度匹配，但是它所做的是利用了"mapReduce"的本质(不仅限于MongoDB)，还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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