How to get only not joined (excluded) documents between two collections? - node.js

Question

The problem is around two collections Users and Forms. Each user is joined with his form by Id.So every form in a Forms collection has a userId foreign key.
I need to get all documents from a Users collection , which doesn't have any form connected to it (there is no such a form).
In SQL I would do something like this:
SELECT *
FROM Users U
LEFT JOIN Forms F
ON U._id= F.userId
WHERE F.userId IS NULL
U=A , F=B
How can we achieve this functionality in MongoDb , may be with Mongoose on a nodeJs side? I couldn't find any solution based on a $lookup aggregation.
Schemas:
*employeeId is a reference to Users _id
let FormsSchema = new Schema({
employeeId:{
type:Schema.Types.ObjectId , ref:'User'
},
companyId:{
type:Schema.Types.ObjectId
},
formData : {
type:String
},
formType : {
type:String
},
formDate :{
type:Date,default: Date.now
},
formState: {
type: String, required: true, enum: ["new","draft","aproved","pendingHR","pendingEMP","pendingSigned"], default: "new"
},
messageData : {
type:Schema.Types.Mixed
},
formIdkunDate:{
type:Date,default: Date.now
},
attachmentDirty:{
type:Boolean
},
company : {
type:Schema.Types.Mixed
},
formShnatMas : {
type:String
},
sendDate : {
type:Date,default: Date.now
},
draftDate : {
type:Date,default: Date.now
},
fixDate : {
type:Date,default: Date.now
},
is101FormOpenedAfterArchive : {
type:Boolean
},
}
let UserSchema = new Schema({
userName:{
type:String,
trim:true
},
CreateDate :{
type:Date,default: Date.now
},
UpdateDate :{
type:Date,default: Date.now
},
password : {
type:String,
required: true,
trim:true
},
isFirstEntrance : {
type:Boolean
},
resetToken : {
type:String
},
resetPasswordExpires : {
type:String
},
resetOtpPassExpires : {
type:String
},
otpPass : {
type:String,
trim:true
},
userType: {
type: String, required: true, enum: ["employee","hr","admin"], default: "employee"
} ,
employeeData : {
type:Schema.Types.Mixed
},
partnerData : {
type:Schema.Types.Mixed
},
externalId : {
type:String
},
isChangedFromPrevious : {
type:Boolean
},
isFirstYearWorker101 : {
type:Boolean
},
lastLogin :{
type:Number
},
loginAttempts : {
type:Number
},
});

Answer 1

I have followed the schema given by you and I am able to get all documents from a Users collection , which doesn't have any form connected to it using $lookup. Please use below aggregate query
db.user.aggregate([
{
$lookup:{
"localField": "_id",
"from": "form",
"foreignField": "employeeId",
"as": "forminfo"
}
},{
$match:{
forminfo: {$size: 0}
}
}
])