如何排序在MongoDB中收集记录中数组 [英] how to sort array inside collection record in mongoDB

问题描述

MongoDB的小白在这里...

MongoDB noob here...

好吧，我有个同学的集合，每个看起来像下面的....我要排序的类型的记载：'功课'按降序排列得分

Ok, I have a collection of students, each with a record that looks like the following.... I want to sort the 'type' : 'homework' scores in descending order.

这是什么咒语看起来像蒙戈的壳呢？

what does that incantation look like on the mongo shell?

> db.students.find({'_id': 1}).pretty()
{
        "_id" : 1,
        "name" : "Aurelia Menendez",
        "scores" : [
                {
                        "type" : "exam",
                        "score" : 60.06045071030959
                },
                {
                        "type" : "quiz",
                        "score" : 52.79790691903873
                },
                {
                        "type" : "homework",
                        "score" : 71.76133439165544
                },
                {
                        "type" : "homework",
                        "score" : 34.85718117893772
                }
        ]
}

我想这个咒语......

I'm trying this incantation....

 doc = db.students.find()

 for (_id,score) in doc.scores:
     print _id,score

但它不工作。

推荐答案

您将需要处理应用程序中的code中的嵌入式阵列，或使用新的 MongoDB中2.2聚合框架

You will need to manipulate the embedded array in your application code or using the new Aggregation Framework in MongoDB 2.2.

在蒙戈 Shell实例聚集：

Example aggregation in the mongo shell:

db.students.aggregate(
    // Initial document match (uses index, if a suitable one is available)
    { $match: {
        _id : 1
    }},

    // Expand the scores array into a stream of documents
    { $unwind: '$scores' },

    // Filter to 'homework' scores 
    { $match: {
        'scores.type': 'homework'
    }},

    // Sort in descending order
    { $sort: {
        'scores.score': -1
    }}
)

示例输出：

{
    "result" : [
        {
            "_id" : 1,
            "name" : "Aurelia Menendez",
            "scores" : {
                "type" : "homework",
                "score" : 71.76133439165544
            }
        },
        {
            "_id" : 1,
            "name" : "Aurelia Menendez",
            "scores" : {
                "type" : "homework",
                "score" : 34.85718117893772
            }
        }
    ],
    "ok" : 1
}

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