How to get conversation list between two user in MongooseJs - node.js

Question

i'm new to MongoDB and trying to build a simple chat app using Node.Js and MongoDB using mongoose Js. and i'm stuck here for last 2 days so need help!!
Tested most of the related answer of stack overflow but not getting desirable result.
What i want to achieve is something similar we see in chat application like Facebook Messenger and whatsApp web where in one side we see all our conversation list which show last message and person profile.
an example here http://roba.laborasyon.com/demos/dark/ (left sidebar)
this is how my model look like
const chat = new Schema({
to:{
type:Schema.Types.ObjectId,
ref:"User",
required:true,
},
from:{
type:Schema.Types.ObjectId,
ref:"User",
required:true,
},
seenbySender:Boolean,
seenByReceiver:Boolean,
isFile:{
type:Boolean,
default:false
},
file:{
type:Object,
required:false,
},
text:String,
},{timestamps:true});
In My Controller or route file (this is not my code but i tried similar logic they all return empty array or error)
exports.test = (request,response,next) => {
let {user} = request.body;
const u=await User.findById(user);
//Chat.find({from:user}).populate('from').populate('to').then(r => response.json(r));
//user ="5f46319ac483a43d98ae3626";
Chat.aggregate([
{$match:{$or:[{"to":user},{"from":user}]}},
{
$group:{"_id":
{
"text":{
$cond:[
{
$gt:[
{$substr:["$to",0,1]},
{$substr:["$from",0,1]}]
},
{$concat:["$to"," and ","$from"]},
{$concat:["$from"," and ","$to"]}
]
}
},
"text":{$first:"$text"}
}
}]).then(result => {
response.json(result)
}).catch(error => {
console.log("[[error]]",error)
response.json({error})
});
}
Here is data i'm working with (exported JSON file)
[
{
"_id": {
"$oid": "5f4a3ae0a7ff491f3024668e"
},
"isFile": false,
"to": {
"$oid": "5f46325ec483a43d98ae3627"
},
"from": {
"$oid": "5f46319ac483a43d98ae3626"
},
"text": "Hi John,Yash here!",
"createdAt": {
"$date": "2020-08-29T11:24:16.416Z"
},
"updatedAt": {
"$date": "2020-08-29T11:24:16.416Z"
},
"__v": 0
},
{
"_id": {
"$oid": "5f4a3affa7ff491f3024668f"
},
"isFile": false,
"to": {
"$oid": "5f46319ac483a43d98ae3626"
},
"from": {
"$oid": "5f46325ec483a43d98ae3627"
},
"text": "hello Yash - John",
"createdAt": {
"$date": "2020-08-29T11:24:47.519Z"
},
"updatedAt": {
"$date": "2020-08-29T11:24:47.519Z"
},
"__v": 0
},
{
"_id": {
"$oid": "5f4a3b25a7ff491f30246690"
},
"isFile": false,
"to": {
"$oid": "5f4632c8c483a43d98ae3628"
},
"from": {
"$oid": "5f46319ac483a43d98ae3626"
},
"text": "Hello Don, Yash this side.",
"createdAt": {
"$date": "2020-08-29T11:25:25.067Z"
},
"updatedAt": {
"$date": "2020-08-29T11:25:25.067Z"
},
"__v": 0
}
]
So what i need is last message of user he chatted with, with the user reference. in this case for Id: 5f46319ac483a43d98ae3626 the last 2 objects should be render
Thanks a lot!!

Answer 1

You can try using $split to get limited records,
db.collection.aggregate([
{
$match: {
$or: [
{ "to": ObjectId("5f46319ac483a43d98ae3626") },
{ "from": ObjectId("5f46319ac483a43d98ae3626") }
]
}
},
// for descending order
{ $sort: { updatedAt: -1 } },
{
$group: {
_id: {
$cond: [
{ $eq: ["$to", ObjectId("5f46319ac483a43d98ae3626")] },
{ $concat: [{ $toString: "$to" }, " and ", { $toString: "$from" }] },
{ $concat: [{ $toString: "$from" }, " and ", { $toString: "$to" }] }
]
},
updatedAt: { $first: "$updatedAt" },
// push messages
messages: { $push: "$$ROOT" }
}
},
// order by descending order
{ $sort: { updatedAt: -1 } },
// limit to 2 messages only
{ $addFields: { messages: { $slice: ["$messages", 2] } } }
])
Playground
for joining user data you can use $lookup

Answer 2

I guess you can use this schema for a chat
MessageSchema = new mongoose.Schema({
from: {
type: string,
required: true,
},
to: {
type: string,
required: true,
},
time: {
type: Date,
default: Date.now(),
},
message: {
type: string,
required: true,
},
});
ChatSchema = new mongoose.Schema({
firstUserId:{
type: mongoose.Schema.Types.ObjectId,
required: true,
},
secondUserId:{
type: mongoose.Schema.Types.ObjectId,
required: true,
},
Chat: MessageSchema,
})
and data will be as this way
[
{
firstUserId: "hjakdsf323275lks",
secondUserId: "asdfe2342232aas",
Chat: [
{
from: "hjakdsf323275lks",
to: "asdfe2342232aas",
time: "18/7/2020 20:06:09",
message: "Hi ",
},
{
from: "asdfe2342232aas",
to: "hjakdsf323275lks",
time: "18/7/2020 21:07:09",
message: "hello ",
},....
],
},
];