Mongoose find last messages grouping by two fields - node.js

Question

I would like to put together a contact list based on the last messages sent or received from a contact.
To do this, I have to sort the last messages (both sent and received), add them and return the last one.
My response should be in the following format:
{
"success": true,
"chatlist": [
{
"id_user": "54228fe2c0df8d1120ed091b",
"lastMessage": {
"content": "message 6",
"date": "2016-11-09T02:54:41.687Z"
},
"unreadMessages": 3,
"name": "user 1"
},
{
"id_user": "12228fe2c0df8d11204g4d",
"lastMessage": {
"content": "message 3",
"date": "2016-11-09T02:54:23.329Z"
},
"unreadMessages": 2,
"name": "user 2"
},
{
"id_user": "58228fe2c0df8d1120e12sd",
"lastMessage": {
"content": "message 1",
"date": "2016-11-09T02:54:19.313Z"
},
"unreadMessages": 1,
"name": "user 3"
}
],
"pages": 2
}
My User Schema is:
var schema = new Schema({
name: {type: String, required: true},
email: {type: String, required: true, unique: true},
password: {type: String, required: true, select: false},
created_at: {type: Date, required: true, default: Date.now}
});
My Message Schema is:
var schema = new Schema({
content: {type: String, required: true},
type: {type: String, required: true, default: 'text'},
status: {type: String, default: 'not_read'},
created_at: {type: Date, default: Date.now},
read_at: {type: Date},
userFrom: {type: Schema.Types.ObjectId, ref: 'User', required: true},
userTo: {type: Schema.Types.ObjectId, ref: 'User', required: true}
});
I have tryed this:
var itensPerPage = 15;
var skip = page !== undefined ? page * itensPerPage : 0;
pages = Math.ceil(pages / itensPerPage);
Message
.aggregate([
{ '$sort': {
'created_at': -1
}},
{ "$skip": skip },
{ "$limit": itensPerPage },
{ '$match': {
$or: [
{ userFrom: user.id_user },
{ userTo: user.id_user }
]
}},
{ '$group': {
'_id': {
'userFrom': '$userFrom',
'userTo': '$userTo'
},
}
},
])
.exec(function (err, messages) {
res.send({"success": true, "chatlist": messages, "pages": pages});
});
How can I modify my query to get the desired response?
Thank you.

Answer 1

Try this
var itensPerPage = 15;
var skip = page !== undefined ? page * itensPerPage : 0;
pages = Math.ceil(pages / itensPerPage);
Message
.aggregate([
{ '$sort': {
'created_at': -1
}},
{ "$skip": skip },
{ "$limit": itensPerPage },
{ '$match': {
$or: [
{ userFrom: user.id_user },
{ userTo: user.id_user }
]
}},
{$unwind : $chatlist},
{$sort : {chatlist.date : -1}},
{$group : {_id : $_id},chatlist : {$push : $chatlist}},
])
.exec(function (err, messages) {
res.send({"success": true, "chatlist": messages, "pages": pages});
});