如何在mongoDB中对集合记录中的数组进行排序

Question

如何在mongoDB中对集合记录中的数组进行排序MongoDB noob在这里......好的，我有一个学生集合，每个都有一个如下所示的记录....我想按照降序排序'类型'：'家庭作业'分数。那个咒语在mongo shell上是什么样的？> 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                 }         ]}我正在尝试这个咒语.... doc = db.students.find()  for (_id,score) in doc.scores:      print _id,score但它不起作用。

Answer 1

您需要在应用程序代码中操作嵌入式数组，或在MongoDB 2.2中使用新的聚合框架。

mongoshell中的示例聚合：

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
    }})

样本输出：

{
    "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}

Answer 2

这就是我们用JS和mongo控制台解决这个问题的方法：

db.students.find({"scores.type": "homework"}).forEach(
  function(s){
    var sortedScores = s.scores.sort(
      function(a, b){
        return a.score<b.score && a.type=="homework";
      }
    );
    var lowestHomeworkScore = sortedScores[sortedScores.length-1].score;
    db.students.update({_id: s._id},{$pull: {scores: {score: lowestHomeworkScore}}}, {multi: true});
  })

Answer 3

这是java代码，可用于找出数组中的最低分数并将其删除。

public class sortArrayInsideDocument{public static void main(String[] args) throws UnknownHostException {
    MongoClient client = new MongoClient();
    DB db = client.getDB("school");
    DBCollection lines = db.getCollection("students");
    DBCursor cursor = lines.find();
    try {
        while (cursor.hasNext()) {
            DBObject cur = cursor.next();
            BasicDBList dbObjectList = (BasicDBList) cur.get("scores");
            Double lowestScore = new Double(0);
            BasicDBObject dbObject = null;
            for (Object doc : dbObjectList) {
                BasicDBObject basicDBObject = (BasicDBObject) doc;
                if (basicDBObject.get("type").equals("homework")) {
                    Double latestScore = (Double) basicDBObject                            .get("score");
                    if (lowestScore.compareTo(Double.valueOf(0)) == 0) {
                        lowestScore = latestScore;
                        dbObject = basicDBObject;

                    } else if (lowestScore.compareTo(latestScore) > 0) {
                        lowestScore = latestScore;
                        dbObject = basicDBObject;
                    }
                }
            }
            // remove the lowest score here.
            System.out.println("object to be removed : " + dbObject + ":"
                    + dbObjectList.remove(dbObject));
            // update the collection
            lines.update(new BasicDBObject("_id", cur.get("_id")), cur,
                    true, false);
        }
    } finally {
        cursor.close();
    }}}