如何在数组字段中对子文档进行排序? [英] How to sort sub-documents in the array field?

问题描述

我正在使用MongoDB Shell来获取一些结果，命令.这是一个采样器，

I'm using the MongoDB shell to fetch some results, ordered. Here's a sampler,

{
"_id" : "32022",
"topics" : [
    {
        "weight" : 281.58551703724993,
        "words" : "some words"
    },
    {
        "weight" : 286.6695125796183,
        "words" : "some more words"
    },
    {
        "weight" : 289.8354232846977,
        "words" : "wowz even more wordz"
    },
    {
        "weight" : 305.70093587160807,
        "words" : "WORDZ"
    }]
}

我想要得到的是相同的结构，但按"topics" : []

what I want to get is, same structure, but ordered by "topics" : []

{
"_id" : "32022",
"topics" : [
    {
        "weight" : 305.70093587160807,
        "words" : "WORDZ"
    },
    {
        "weight" : 289.8354232846977,
        "words" : "wowz even more wordz"
    },
    {
        "weight" : 286.6695125796183,
        "words" : "some more words"
    },
    {
        "weight" : 281.58551703724993,
        "words" : "some words"
    },
    ]
}

我设法获得了一些有序的结果，但是按ID字段对它们进行分组没有运气.有办法吗?

I managed to get some ordered results, but no luck in grouping them by id field. is there a way to do this?

推荐答案

MongoDB没有提供开箱即用的方法，但是有一种解决方法是更新您的文档并使用

MongoDB doesn't provide a way to do this out of the box but there is a workaround which is to update your documents and use the $sort update operator to sort your array.

db.collection.update_many({}, {"$push": {"topics": {"$each": [], "$sort": {"weight": -1}}}})

您仍然可以像这样使用.aggregate()方法:

You can still use the .aggregate() method like this:

db.collection.aggregate([
    {"$unwind": "$topics"}, 
    {"$sort": {"_id": 1, "topics.weight": -1}}, 
    {"$group": {"_id": "$_id", "topics": {"$push": "$topics"}}}
])

但是，如果您只想对数组进行排序，则效率会降低，并且您绝对不应该这样做.

But this is less efficient if all you want is sort your array, and you definitely shouldn't do that.

您总是可以使用 .sort 或 sorted 函数.

You could always do this client side using the .sort or sorted function.

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