MongoDB aggregation: Check if user has already rated a product - node.js

Question

I'm having some trouble coming up with a solution to this problem by using mongo directly instead of node.
I have a collection of products that have several fields, including an array of ratings. The ratings consist of the id of the user who rated it and the score. They look like this:
{
"_id": {
"$oid": "62812fac06f29f5fe874c0db"
},
"model": "fire",
"allRatings": [
{
"user_id": "6282962e3aa8163084776092",
"rating": 9
},
{
"user_id": "62811d520f52b64990a94e99",
"rating": 6
}
],
}
I'd like to return all of the fields, but instead of all the ratings, I just want to return a boolean that shows if the current user, whose ID I have in the code, has already rated the product. I have tried with aggregations, but haven't found any solution that works.
Something like this:
{
"_id": {
"$oid": "62812fac06f29f5fe874c0db"
},
"model": "fire",
"hasRated": true,
}

Answer 1

If I've understood correctly you can use this aggregation query:
This query looks for the object you want (matching by _id) and then, into a $project stage it set the value hasRated if the desired id exists into the array.
db.collection.aggregate([
{
$match: {
_id: ObjectId("62812fac06f29f5fe874c0db")
}
},
{
$project: {
model: 1,
hasRated: {
"$in": [
"6282962e3aa8163084776092",
"$allRatings.user_id"
]
}
}
}
])
Example here
To do in JS you can simply create the object adding the id as a variable (something like this, is pseudocode, not tested):
const id = 'your_id_here'
const agg = [{
$match: {
_id: new ObjectId("62812fac06f29f5fe874c0db")
}
},
{
$project: {
model: 1,
hasRated: {
"$in": [
id,
"$allRatings.user_id"
]
}
}
}]
db.aggregate(agg)