schema to messages on mongoDb

//schema
var messages_schema = mongoose.Schema({
    from: mongoose.Schema.Types.ObjectId
    ,to: mongoose.Schema.Types.ObjectId
    ,created_on: Date
    ,delivered_on: Date
    ,message: String
});


//update devilered_on
messagesDb.db.update({to:to, from:from, delivered_on:null}, {$set:{delivered_on:now}}, {multi:true}, function(err, result){
    if(err) {
        console.log(err);
        deferred.reject();
        return;
    }

    if(that.users[from]){
        that.users[from].notifyDelivery(to, now);
    }

    deferred.resolve(now);
});

//get unread messages
 messagesDb.db.find({to:id, delivered_on:null}).distinct('from').exec( function(err, results){
    if(err){
        console.log('erro ao obter mensagens não lidas', err);
        return;
    }
    deferred.resolve(results);
});

//get history
messagesDb.db.find({
    $or:[
        {from:id, to:id2}
        ,{from:id2, to:id}
    ]
}).sort({'created_on': -1}).skip(skip).limit(limit).exec( function(err, results){
    if(err){
        res.json(err);
        console.log('erro ao obter histórico', err);
        return;
    }
    var messages = [];
    for(var i=results.length-1;i>-1;i--){
        messages.push({
            id:results[i]._id
            ,message:results[i].message
            ,from:results[i].from
            ,to:results[i].to
            ,created_on:results[i].created_on
            ,delivered_on:results[i].delivered_on
        });
    }

    deferred.resolve(messages);

});