How to sort array inside collection record in MongoDB?

Question

I have a collection of students, each with a record that looks like the following and I want to sort the scores array in descending order of score.

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                 }         ] } 

I'm trying this incantation....

 doc = db.students.find()   for (_id,score) in doc.scores:      print _id,score 

but it's not working.

Answer 1

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

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     }} ) 

Sample output:

{     "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 }