mongoose, nodejs, sort by date in a subdocument

Question

I have problem trying to do a sort by date of updated_at "post" (subdocument), with the code below i see the posts in order of creation. I need sort by date of updated.

var postSchema = new mongoose.Schema({
    post: String,
    created_at: { type: Date, default: Date.now },
    updated_at: Date
});

var UserSchema = new mongoose.Schema({
    username: String,
    password: String,
    posts: [postSchema]
});


app.get("/val",isLoggedIn, function(req, res){
    var aca = req.user._id; 
    User.findById({_id: aca},function(err, myposts){
       if(err){
           console.log(err);
       } else {
           res.render("index", {dataposts:myposts});
       }
    });
    });

Answer 1

I would suggest following, using $order_by

User.findById({ $query : {_id: aca},$orderby: {updated_date: -1} })

In latest versions of mongoose this should work,

User.findById({_id: aca}).sort({updated_at:-1}).exec(function(err, myposts) {... });