javascript - How can I sort array by a field inside a MongoDB document -

i have document called question

var questionschema = new schema({     title: {         type: string,         default: '',         trim: true     },     body: {         type: string,         default: '',         trim: true     },     user: {         type: schema.objectid,         ref: 'user'     },     category: [],     comments: [{         body: {             type: string,             default: ''         },         root: {             type: string,             default: ''         },         user: {             type: schema.types.objectid,             ref: 'user'         },         createdat: {             type: date,             default: date.now         }     }],     tags: {         type: [],         get: gettags,         set: settags     },     image: {         cdnuri: string,         files: []     },     createdat: {         type: date,         default: date.now     } }); 

as result, need sort comments root field,

i tried sort array of comments manually @ backend , tried use aggregation, not able sort this. please.

presuming question model object in code , of course want sort "comments "date" createdat using .aggregate() use this:

question.aggregate([     // ideally match document want     { "$match": { "_id": docid } },      // unwind array contents     { "$unwind": "comments" },      // sort on array contents per document     { "$sort": { "_id": 1, "comments.createdat": 1 } },      // group structure     { "$group": {         "_id": "$_id",         "title": { "$first": "$title" },         "body": { "$first": "$body" },         "user": { "$first": "$user" },         "comments": { "$push": "$comments" },         "tags": { "$first": "$tags" },         "image": { "$first": "$image" },         "createdat": { "$first": "$createdat" }     }} ], function(err,results) {     // sorted results }); 

but overkill since not "aggregating" between documents. use javascript methods instead. such .sort():

quesion.findonebyid(docid,function(err,doc) {     if (err) throw (err);     var mydoc = doc.toobject();     mydoc.questions = mydoc.questions.sort(function(a,b) {         return a.createdat > b.createdat;     });    console.log( json.stringify( doc, undefined, 2 ) ); // intented nicely }); 

so whilst mongodb have "tools" on server, makes sense in client code when retrieve data unless need "aggregate" accross documents.

but both example usages have been given now.