How to inner join in mongodb. (aggregation) - mongodb

Question

What i want to do is find out which post i have reacted to and return true or false as below result i expect. i know about aggregation in mongodb but i don't know how it works yet. If anyone has study material about it, please comment. thank you.
// user model
{
"_id": "62d0d2e8306367e5162b9c4e",
"fullname": "string",
"username": "string",
"avatar": "string",
"bio": "string",
"tick": true,
"followings_count": 55,
"followers_count": 5,
"likes_count": 0,
"website_url": "",
"social_network": [],
"created_at": "2022-07-15T02:37:28.565Z",
"updated_at": "2022-08-23T08:23:16.611Z",
"__v": 0
}
// post model
{
"_id": "62f0ad6cca2731b7a851b5a5",
"contents": ":>>",
"media_url": "string",
"reaction_count": 1,
"view_count": 0,
"category_id": [],
"created_at": "2022-08-08T06:30:04.137Z",
"updated_at": "2022-08-24T04:10:33.944Z",
"__v": 0,
"comment_count": 9
}
// post_reaction model
{
"user_id": "62d0d2e8306367e5162b9c4e",
"post_id":"62f0ad6cca2731b7a851b5a5",
"type": "Like",
}
This is the result i expect:
{
"data": {
"user": {
"_id": "62d0d2e8306367e5162b9c4e",
...
},
"post": [
{
"_id": "62f0ad6cca2731b7a851b5a5",
...
"is_reaction": true(false)),
},
...
]
}

Answer 1

I found the way resolve this issues:
const result = await PostModel.aggregate([
{
$match: { user_id: ObjectUserId },
},
{
$lookup: {
from: 'post_reaction',
localField: '_id',
foreignField: 'post_id',
as: 'isReaction',
},
},
{
$project: {
_id: 1,
contents: 1,
media_url: 1,
reaction_count: 1,
view_count: 1,
category_id: 1,
created_at: 1,
updated_at: 1,
comment_count: 1,
isReaction: {
$filter: {
input: '$isReaction',
cond: {
$eq: ['$$this.user_id', ObjectUserId],
},
},
},
},
},
{ $sort: { _id: -1 } },
]);