how to update data after using aggregate in nodejs mongodb

Question

Hi im new to nodejs and mongodb What I want to do after executing my aggregate command is to drop the lowest score that the aggregate command has found.. This is my code:

MongoClient.connect('mongodb://localhost:27017/school', function(err, db) {
    if(err) throw err;

    var students = db.collection("students");

    students.aggregate( [ { "$unwind": "$scores" },
    {"$group": { '_id':'$_id' , 'score': {'$min': "$scores.score" } } }],function(err, result){
            if(err) throw err;
            for(var i=0; i<200; i++){
                //console.log(result[i].score);
                updateStudents(result[i]._id,result[i].score);
            }
    });


    function updateStudents(_id,score){
        var query = {'_id':_id};
        var operator = {'$unset' : {'scores.score' : score}};
        var options = {multi : true};

        students.update(query,operator,options,function(err,updated){
            if(err) throw err;
            console.dir('Successfully Updated' + updated);
        });
    }

});

It says that it has updated successfully but when I check it via query, it has not dropped the lowest score of the users.

this is what the schema looks like:

db.students.find({'_id':0}).pretty()
{
    "_id" : 0,
    "name" : "aimee Zank",
    "scores" : [
        {
            "type" : "exam",
            "score" : 1.463179736705023
        },
        {
            "type" : "quiz",
            "score" : 11.78273309957772
        },
        {
            "type" : "homework",
            "score" : 6.676176060654615
        },
        {
            "type" : "homework",
            "score" : 35.8740349954354
        }
    ]
}

I would like to drop the first element which has the lowest score but cant

jillro · Accepted Answer · 2014-02-01 17:47:26Z

2

Your function updateStudents set up a callback which close the connection return db.close();

So obviously if one update finishes and call the callback before you have made all updates, you have this MongoError: Connection Closed By Application error.

You should not close connection after request in a node.js app. You should use always the same connection, passing it through your application to all modules needing it.

To remove value from array, you should not use $unset which is use to drop entire fields. You should use : var operator = {'$pull' : {'scores' : {'score' : score} } }; which will remove the value score from the array scores.

edited Feb 1, 2014 at 17:47

answered Feb 1, 2014 at 16:59

jillro

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1 Comment

Monece Solis Over a year ago

hi, thanks for the reply. I have updated my question, the error was gone but it seems my update is still not working properly. It says it has updated but when I checked the db via query it did not $unset any of the score that has the lowest score to the users. why is this?

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