How to check $setDifference in two array using mongo-query - mongodb

Question

UserDetails
{
"_id" : "5c23536f807caa1bec00e79b",
"UID" : "1",
"name" : "A",
},
{
"_id" : "5c23536f807caa1bec00e78b",
"UID" : "2",
"name" : "B",
}
UserProducts
{
"_id" : "5c23536f807caa1bec00e79c",
"UPID" : "100",
"UID" : "1"
},
{
"_id" : "5c23536f807caa1bec00e79c",
"UPID" : "200",
"UID" : "2"
}
Groups
{
"_id" : "5bb20d7556db6915846da55f",
"members" : {
"regularStudent" : [
"200" // UPID
],
}
}
Step 1
I have to take UID from UserDetails check with UserProducts then take UPID from UserProducts
Step 2
we have to check this UPID mapped to Groups collection or not ?.
members.regularStudent we are mapped UPID
Step 3
Suppose UPID not mapped means i want to print the UPID from from UserProducts
I have tried but couldn't complete this, kindly help me out on this.
Expected Output:
["100"]
Note: Expected Output is ["100"] , because UserProducts having UPID 100 & 200 but Groups collection mapped only 200.
My Code
db.UserDetails.aggregate(
{
$lookup: {
from: "UserProducts",
localField: "UID",
foreignField: "UID",
as: "userProduct"
}
},
{ $unwind: "$userProduct" },
{
"$project": { "_id" : 0, "userProduct.UPID" : 1 }
},
{
$group: {
_id: null,
userProductUPIDs: { $addToSet: "$userProduct.UPID" }
}
}
) // returns [ "100", "200" ]
db.Groups.aggregate([
{
$unwind: "$members.regularStudent"
},
{
$group: {
_id: null,
UPIDs: { $addToSet: "$members.regularStudent" }
}
}
]) // returns ["200"]
Now i want to check $setDifference of both array, so i had added below code but returning error like $userProductUPIDs is not defined
db.Groups.aggregate([
{
$unwind: "$members.regularStudent"
},
{
$group: {
_id: null,
UPIDs: { $addToSet: "$members.regularStudent" }
}
},
{
$project: {
members: {
$setDifference: [ $userProductUPIDs , "$members" ]
},
_id : 0
}
}
])

Answer 1

As this is a follow up to one of my previous answers I will try to fix your code. The bottom line is that you need two queries as you can't upgrade your database so the code should look like below:
var queryResult = db.UserDetails.aggregate(
{
$lookup: {
from: "UserProducts",
localField: "UID",
foreignField: "UID",
as: "userProduct"
}
},
{ $unwind: "$userProduct" },
{
"$project": { "_id" : 0, "userProduct.UPID" : 1 }
},
{
$group: {
_id: null,
userProductUPIDs: { $addToSet: "$userProduct.UPID" }
}
});
let userProductUPIDs = queryResult.toArray()[0].userProductUPIDs;
db.Groups.aggregate([
{
$unwind: "$members.regularStudent"
},
{
$group: {
_id: null,
UPIDs: { $addToSet: "$members.regularStudent" }
}
},
{
$project: {
members: {
$setDifference: [ userProductUPIDs , "$UPIDs" ]
},
_id : 0
}
}
]) // should return 100