Query a MongoDB collection by the property of an embedded relation - node.js

Question

I am trying to find documents in a collection, but filtered based on the value of an embedded ObjectID relation.
Mongoose schema is as follows:
const UserQualificationSchema = new Schema(
{
user: {
type: mongoose.Schema.Types.ObjectId,
ref: 'User',
},
}
const UserSchema = new Schema(
{
fleet: {
type: [String], // Eg ["FleetA", "FleetB", "FleetC"]
required: true,
}
}
I need to find all UserQualifications where an item in the user's fleet equals a value in a filter array.
For example: Find all User Qualifications where user.fleet: {$in: ["FleetA", "FleetC"]}
I've looked at aggregations and querying inside .populate() but can't seem to get it to work.
Any ideas much appreciated.

Answer 1

Use aggregation query for your problem, I have created a query for you.
users.collection.json
/* 1 */
{
"_id" : ObjectId("61056c4a8cca27df3db2e4c8"),
"firstName" : "Rahul",
"lastName" : "soni",
"fleet" : [
"FleetA",
"FleetB",
"FleetC"
],
"createdAt" : ISODate("2021-07-31T15:29:14.918Z")
}
userqualifications.collection.json
/* 1 */
{
"_id" : ObjectId("61056c908cca27df3db2e4c9"),
"user" : ObjectId("61056c4a8cca27df3db2e4c8"),
"createdAt" : ISODate("2021-07-31T15:30:24.510Z")
}
aggregation query:
it will get the result only if a user has FleetA and FleetC.
if anyone is not matched then it will return 0 records
db.userqualifications.aggregate([{
"$lookup": {
"from": "users",
"localField": "user",
"foreignField": "_id",
"as": "user"
}
}, {
"$unwind": "$user"
}, {
"$match": {
"user.fleet": {
"$elemMatch": {
"$eq": "FleetA",
"$eq": "FleetC"
}
}
}
}])
Result:
/* 1 */
{
"_id" : ObjectId("61056c908cca27df3db2e4c9"),
"user" : {
"_id" : ObjectId("61056c4a8cca27df3db2e4c8"),
"firstName" : "Rahul",
"lastName" : "soni",
"fleet" : [
"FleetA",
"FleetB",
"FleetC"
],
"createdAt" : ISODate("2021-07-31T15:29:14.918Z")
},
"createdAt" : ISODate("2021-07-31T15:30:24.510Z")
}

Answer 2

if the goal is to get only UserQualifications then the following should be an efficient way as it can use an index on the fleet field of the User collection.
db.User.aggregate([
{
$match: {
fleet: { $in: ["FleetA", "FleetB"] }
}
},
{
$lookup: {
from: "UserQualification",
localField: "_id",
foreignField: "user",
as: "qualifications"
}
},
{
$unwind: "$qualifications"
},
{
$replaceWith: "$qualifications"
}
])
on the other hand if you start from the UserQualifications collection, you can't efficiently narrow down the records as you're filtering on something that it doesn't have the data for.

Answer 3

Thank you for the answer - it did achieve the results I was looking for - however I am now struggling to add a $match with $and to the aggregate to only return the qualifications where the user ID equals one inside a submitted array AND a given fleet.
I have the following aggregate:
db.UserQualifications.aggregate([{
{
$lookup: {
from: 'users',
localField: 'user',
foreignField: '_id',
as: 'user',
},
},
{
$unwind: '$user',
},
{
$match: {
$and: [
'user.fleet': {
$in: ["Fleet A", "Fleet C"], // This works on it's own
},
user: { // Also tried 'user._id'
$in: ["6033e4129070031c07fbbf29"] // Adding this returns blank array
}
]
},
}
}])
I have double checked that I am passing in the correct User ID's inside the arrays, but when I add this to the $and inside match, it only returns a blank array.
Is there another way to do this?

Answer 4

// Updated users collection
/* 1 */
{
"_id" : ObjectId("61056c4a8cca27df3db2e4c8"),
"firstName" : "Rahul",
"lastName" : "soni",
"fleet" : [
"Fleet A",
"Fleet B",
"Fleet C"
],
"createdAt" : ISODate("2021-07-31T15:29:14.918Z")
}
Query:
// userqualifications => this is my collection name, you can add your collection name here db.<YOUR>
db.userqualifications.aggregate([{
$lookup: {
from: 'users',
localField: 'user',
foreignField: '_id',
as: 'user',
},
},
{
$unwind: '$user',
},
{
$match: {
// $and operatory syntax [{}, {}]
$and: [{
'user.fleet': {
// "Fleet A", "Fleet C" (FleetA, FleetC) this is the my first options,
// I have changes according to your problem
$in: ["Fleet A", "Fleet C"], // This works on it's own
}
}, {
// Convert user id to ObjectId type (_bsonType)
"user._id": ObjectId("61056c4a8cca27df3db2e4c8")
}]
}
}
])
Result:
/* 1 */
{
"_id" : ObjectId("61056c908cca27df3db2e4c9"),
"user" : {
"_id" : ObjectId("61056c4a8cca27df3db2e4c8"),
"firstName" : "Rahul",
"lastName" : "soni",
"fleet" : [
"Fleet A",
"Fleet B",
"Fleet C"
],
"createdAt" : ISODate("2021-07-31T15:29:14.918Z")
},
"createdAt" : ISODate("2021-07-31T15:30:24.510Z")
}
Difference Image: