Not able to receive expected result in mongodb between collections - mongodb

Question

I'm trying to get a product list with logged user wishlist in the product list itself. I'm trying $lookup but not getting the expected result.
Product Document:
[
{
"_id" : ObjectId("6044351794bee8b6e0fce48f"),
"sku" : "P003474",
"name" : "Kitchen Wash"
},
{
"_id" : ObjectId("6085584c42ad3c58c5dbc6b7"),
"sku" : "TS0012",
"name" : "T-shirt"
},
{
"_id" : ObjectId("608d20a90e629fcc0d3a93e1"),
"sku" : "Apple1101",
"name" : "Green Apple"
}
]
Wishlist Document:
wishlist:
[
{
"_id" : ObjectId("608d8af12b7556c445f5cd87"),
"product" : ObjectId("6044351794bee8b6e0fce48f"),
"user" : ObjectId("601fb31a60e0a024143e6ea3"),
"isLiked" : false
},
{
"_id" : ObjectId("608d8bad2b7556c445f5cd88"),
"product" : ObjectId("6085584c42ad3c58c5dbc6b7"),
"user" : ObjectId("601fb31a60e0a024143e6ea3"),
"isLiked" : true
}
]
Expected Result:
Expected output:
[
{
"_id" : ObjectId("6044351794bee8b6e0fce48f"),
"sku" : "P003474",
"name" : "Kitchen Wash",
"isLiked": false
},
{
"_id" : ObjectId("6085584c42ad3c58c5dbc6b7"),
"sku" : "TS0012",
"name" : "T-shirt",
"isLiked": true
},
{
"_id" : ObjectId("608d20a90e629fcc0d3a93e1"),
"sku" : "Apple1101",
"name" : "Green Apple"
}
]
The query I'm trying:
db.getCollection('products').aggregate([
{
$lookup: {
from: "wishlists",
localField: "_id",
foreignField: "product",
as: "product"
}
},
{
$unwind:"$product"
}
])
Not able to get the above-declared result

Answer 1

$unwind causing the issues, first problem is it will remove document when product lookup result empty/[] if you don't specify preserveNullAndEmptyArrays : true, see working behaviour in playground
use $lookup with pipeline and match product id and user id condition
i have changed as name to isLiked in $lookup
$addFields to add isLiked parameter it its present, $arrayElemAt to get isLiked element from first element
db.getCollection('products').aggregate([
{
$lookup: {
from: "wishlists",
let: { product: "$_id" },
pipeline: [
{
$match: {
$and: [
{ $expr: { $eq: ["$$product", "$product"] } },
{ user: ObjectId("601fb31a60e0a024143e6ea3") }
]
}
}
],
as: "isLiked"
}
},
{
$addFields: {
isLiked: { $arrayElemAt: ["$isLiked.isLiked", 0] }
}
}
])
Playground