Joining mongodb collection based on condition [duplicate] - node.js

Question

This question already has an answer here:
Conditional $lookup in MongoDB?
(1 answer)
Closed 3 years ago.
I have two collections in MongoDB and want to join the two collections based on some condition.
I want to join 'order' and 'order-status' table to get all orders assigned to '123' with status 'ready'
orders
{
"_id":"1",
"name": "Fridge",
"assignee": "123"
},
{
"_id":"2",
"name": "TV",
"assignee": "567"
},
{
"_id":"3",
"name": "Music system",
"assignee": "123"
}
order-status
{
"_id":"1",
"status": "ready",
"orderId": "1"
},
{
"_id":"2",
"status": "cancelled",
"orderId": "2"
},
{
"_id":"3",
"status": "cancelled",
"orderId": "3"
}
assignee
{
"_id":"123",
"name": "Jak"
}
{
"_id":"567",
"name": "Mac"
}
I want to join 'order' and 'order-status' table to get all orders assigned to '123' with status 'ready'
Expecting a final result as
[
{
"_id":"1",
"name": "Fridge",
"assignee": "123",
"status": {
"_id":"1",
"status": "ready",
"orderId": "1"
}
}
]
Tried following but how to check order status in another table with lookup
const resultObject = orders.aggregate([
{ $match : {assignee: Objectid('123')} },
{
$lookup: {
from: 'user-status',
localField: 'assignee',
foreignField : '_id',
as : 'assignee'
}
},
{
$unwind: '$assignee'
}
]);

Answer 1

First you need to use match to filter by "assignee": "123", then you need to lookup order-status, match "orderStatus.status": "ready".
const resultObject = orders.aggregate([
{
$match: {
assignee: "123"
}
},
{
$lookup: {
from: "order-status",
localField: "_id",
foreignField: "orderId",
as: "statuses"
}
},
{
$match: {
"statuses.status": "ready"
}
},
{
$project: {
id: "_id",
name: "$name",
assignee: "$assignee",
status: {
$arrayElemAt: ["$statuses", 0]
}
}
}
]);
This will give result like this:
[
{
"_id": "1",
"assignee": "123",
"name": "Fridge",
"status": {
"_id": "1",
"orderId": "1",
"status": "ready"
}
}
]
Playground

Answer 2

I would use the following pipeline:
const resultObject = orders.aggregate([
{
$match: {
assignee: Objectid('123')
}
},
{
$lookup:
{
from: "order-status",
let: {order_id: "$_id"},
pipeline: [
{
$match:
{
$expr:
{
$and:
[
{$eq: ["$orderId", "$$order_id"]},
{$eq: ["$status", "ready"]}
]
}
}
}
],
as: "stock"
}
},
{
$unwind: "$stock"
},
// now we get the assignee info.
{
$lookup: {
from: 'user-status',
localField: 'assignee',
foreignField: '_id',
as: 'assignee'
}
},
{
$unwind: '$assignee'
},
//finaly create the required structure.
{
$project: {
name: "$assignee.name",
assignee: "$assignee._id",
status: "$stock.0"
}
}
]);