How To Sort This Data in MongoDB?

Question

/* 0 */
{
  "_id" : ObjectId("5380c9e097632cee5b000007"),
  "month" : "5",
  "userid" : "53806aac12c75f4b51000001",
  "__v" : 7,
  "posts" : [{
      "postid" : ObjectId("538185cae0c6b8666e000008"),
      "ts" : ISODate("2014-05-25T05:55:22.976Z"),
      "userid" : "53806aac12c75f4b51000001",
      "name" : "BBB",
      "text" : "b1",
    }]
}

/* 1 */
{
  "_id" : ObjectId("5380c80e97632cee5b000001"),
  "month" : "5",
  "userid" : "5380629ea3b31f864f000001",
  "__v" : 24,
  "posts" : [{
      "postid" : ObjectId("538185b2e0c6b8666e000004"),
      "ts" : ISODate("2014-05-25T05:54:58.703Z"),
      "userid" : "5380629ea3b31f864f000001",
      "name" : "AAA",
      "text" : "a1",
    }, {
      "postid" : ObjectId("538185b7e0c6b8666e000006"),
      "ts" : ISODate("2014-05-25T05:55:03.474Z"),
      "userid" : "5380629ea3b31f864f000001",
      "name" : "AAA",
      "text" : "a2",

    }, {
      "postid" : ObjectId("538185d6e0c6b8666e00000a"),
      "ts" : ISODate("2014-05-25T05:55:34.231Z"),
      "userid" : "5380629ea3b31f864f000001",
      "name" : "AAA",
      "text" : "a3",
    }]
}

This is my DATA.

I want to Sort This Data for 'Ts' ( Data ).

I want That Sorted List by 'posts.Ts' Like this..
name : AAA, text = a3
name : BBB, text = b1
name : AAA, text = a2
name : AAA, text = a1

but i Don't know How to query this. Please Talk To ME

This is my code in Node and mongoose.

db.collection('walls', function(err, collection) {

collection.find(function(err, data) {

collection.aggregate(
{$match: {userid:userid}},
{$project: {posts: 1,_id:0}},
{$sort:{'posts.ts':1}}, 
{$unwind: "$posts"}
)}

...

Answer 1

You are onto the right principles but you have pipeline stages the wrong way around. You need to $unwind the arrays before you sort:

db.collection.aggregate([
    { "$match": { "userId": userId" } },
    { "$project": { "_id": 0, "posts": 1 } },
    { "$unwind": "$posts" },
    { "$sort": { "posts.ts": 1, "posts.name": 1 } }
])