Match a nested object field present in an array in lookup aggregation - node.js

Question

I have two collections Projects and Users.
Projects has a budget field with the following: 1)amount and 2)currency
{
_id: ObjectId(...),
type: 'typeA',
budget: {
amount: 123,
currency: 'USD'
}
}
Users has a field called bids which contains list of objects with fields amount and currency.
{
_id: ObjectId(...),
name: "User name",
bids: [{amount: 123, currency: "USD"}, {amount: 342, currency: "INR"}]
}
I am trying to join Users with Projects using a lookup aggregation.
db.Projects.aggregate([
{
$lookup: {
from: "Users",
let: { projectAmount: "$budget.amount", projectCurrency: "$budget.currency" },
pipeline: [
{$match: {
$expr: {
$and: [
{ $eq: ["$bids.amount", "$$projectAmount"] },
{ $eq: ["$bids.currency", "$$projectCurrency"] }
]
}
}}
],
as: "matchingBids"
}
]);
But I am always getting the empty result though I have some matching objects in the Users collection. I've gone through the official docs and internet but didn't find anything helpful. Any help would be appreciated. Thank you

Answer 1

Try $in operator with full object and array
pass budget object in let
check $in condition with bids array
db.Projects.aggregate([
{
$lookup: {
from: "Users",
let: { budget: "$budget" },
pipeline: [
{
$match: {
$expr: { $in: ["$$budget", "$bids"] }
}
}
],
as: "matchingBids"
}
}
])
Playground
WARNING:
The above approach will work only when order of fields in object and array of object should be same, below examples will not work!
budget: { amount: 123, currency: "USD" }
bids: [{ currency: "USD", amount: 123 }]
OR
budget: { currency: "USD", amount: 123 }
bids: [{ amount: 123, currency: "USD" }]
EDIT:
After some workaround i found a way to make sure to match exact fields to overcome above situation,
$or condition with both possibility of fields position {amount, currency} and {currency, amount}
db.Projects.aggregate([
{
$lookup: {
from: "Users",
let: { budget: "$budget" },
pipeline: [
{
$match: {
$expr: {
$or: [
{
$in: [
{ amount: "$$budget.amount", currency: "$$budget.currency" },
"$bids"
]
},
{
$in: [
{ currency: "$$budget.currency", amount: "$$budget.amount" },
"$bids"
]
}
]
}
}
}
],
as: "matchingBids"
}
}
])
Playground