How to $setDifference in array & Object using Mongo DB - mongodb

Question

UserDetails
{
"_id" : "5c23536f807caa1bec00e79b",
"UID" : "1",
"name" : "A",
},
{
"_id" : "5c23536f807caa1bec00e78b",
"UID" : "2",
"name" : "B",
},
{
"_id" : "5c23536f807caa1bec00e90",
"UID" : "3",
"name" : "C"
}
UserProducts
{
"_id" : "5c23536f807caa1bec00e79c",
"UPID" : "100",
"UID" : "1",
"status" : "A"
},
{
"_id" : "5c23536f807caa1bec00e79c",
"UPID" : "200",
"UID" : "2",
"status" : "A"
},
{
"_id" : "5c23536f807caa1bec00e52c",
"UPID" : "300",
"UID" : "3",
"status" : "A"
}
Groups
{
"_id" : "5bb20d7556db6915846da55f",
"members" : {
"regularStudent" : [
"200" // UPID
],
}
},
{
"_id" : "5bb20d7556db69158468878",
"members" : {
"regularStudent" : {
"0" : "100" // 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:
["300"]
Note: Expected Output is ["300"] , because UserProducts having UPID 100 & 200 but Groups collection mapped only 100& 200.
My Code
var queryResult = db.UserDetails.aggregate(
{
$lookup: {
from: "UserProducts",
localField: "UID",
foreignField: "UID",
as: "userProduct"
}
},
{ $unwind: "$userProduct" },
{ "$match": { "userProduct.status": "A" } },
{
"$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
}
}
])
My Output
{
"members" : [
"300",
"100"
]
}

Answer 1

You need to fix that second aggregation and get all UPIDs as an array. To achieve that you can use $cond and based on $type either return an array or use $objectToArray to run the conversion, try:
db.Groups.aggregate([
{
$project: {
students: {
$cond: [
{ $eq: [ { $type: "$members.regularStudent" }, "array" ] },
"$members.regularStudent",
{ $map: { input: { "$objectToArray": "$members.regularStudent" }, as: "x", in: "$$x.v" } }
]
}
}
},
{
$unwind: "$students"
},
{
$group: {
_id: null,
UPIDs: { $addToSet: "$students" }
}
},
{
$project: {
members: {
$setDifference: [ userProductUPIDs , "$UPIDs" ]
},
_id : 0
}
}
])