Grouping in mongoose aggregation according to condition - node.js

Question

I am building a chat app based on the MERN stack and need to fetch all chats for a specific user.
This is my chat messages schema:
const message = mongoose.Schema({
from: {
type: Schema.Types.ObjectId,
ref: "users",
required: true,
},
to: {
type: Schema.Types.ObjectId,
ref: "users",
required: true,
},
text: { type: String, required: false },
imgLink: { type: String, required: false },
sentAt: { type: Date, required: true },
deliveredAt: { type: Date, required: false },
readAt: { type: Date, required: false },
});
Is there a way to fetch all chats for a user and group them by who sent/recieved these chats.
I used this aggregation pipeline
const fetchChatPipeline = (_id) => {
return [
{
$match: {
$or: [
{
to: mongoose.Types.ObjectId(_id),
},
{
from: mongoose.Types.ObjectId(_id),
},
],
},
},
{
$sort: {
sentAt: 1,
},
},
{
$group: {
_id: "$from",
from: { $first: "$from" },
to: { $first: "$to" },
messages: {
$push: {
text: "$text",
imgLink: "$imgLink",
sentAt: "$sentAt",
deliveredAt: "$deliveredAt",
readAt: "$readAt",
},
},
},
},
{
$lookup: {
from: "users",
localField: "from",
foreignField: "_id",
as: "from",
},
},
{
$unwind: {
path: "$from",
preserveNullAndEmptyArrays: false,
},
},
{
$lookup: {
from: "users",
localField: "to",
foreignField: "_id",
as: "to",
},
},
{
$unwind: {
path: "$to",
preserveNullAndEmptyArrays: false,
},
},
{
$project: {
to: {
_id: 1,
name: 1,
},
from: {
_id: 1,
name: 1,
},
messages: 1,
},
},
];
};
and got the following result:
{
"chats": [
{
"_id": "60368ee8a4e8494c74ccbeec",
"from": {
"_id": "60368ee8a4e8494c74ccbeec",
"name": "Jaivardhan Singh"
},
"to": {
"_id": "603a637ab356a309dcca9099",
"name": "Jai Singh "
},
"messages": [
{
"text": "hello",
"sentAt": "2021-02-27T16:33:40.335Z"
},
{
"text": "What you upto",
"sentAt": "2021-02-27T16:34:16.852Z"
}
]
},
{
"_id": "603a637ab356a309dcca9099",
"from": {
"_id": "603a637ab356a309dcca9099",
"name": "Jai Singh "
},
"to": {
"_id": "60368ee8a4e8494c74ccbeec",
"name": "Jaivardhan Singh"
},
"messages": [
{
"text": "Hi",
"sentAt": "2021-02-27T16:35:32.343Z"
},
{
"text": "Nothing just chilling",
"sentAt": "2021-02-27T16:35:41.720Z"
},
{
"text": "What you upto",
"sentAt": "2021-02-27T16:35:49.662Z"
}
]
}
]
}
Is there a way i can merge these two chats in the results as they have common participants. Thanks.

Answer 1

Just change your $match stage as below and $group it by null
{
$match: {
$or: [
{ to: mongoose.Types.ObjectId(_id) },
{ from: mongoose.Types.ObjectId(_id) }
],
to: { $ne: mongoose.Types.ObjectId(_id) }
}
}