Mongoose Nested Populate Not Working - node.js

Question

So I am currently extremely confused when it comes to mongoose populating.
My data structure is as follows: User has an array of Clients, a Client has an array of loans. I am using User.find and populating the client, no problem. But then how do I populate the loans that is inside of the client? I have tried this:
Basically, the goal is to pass in an array of Clients, each client will contain a loan. But for now, I want that loan object to be empty. The Client is being populated correctly, however, the Loan reference is being passed as undefined.
app.get("/loans", IsLoggedIn, function(req, res) {
User.findById(req.user._id).populate({path: "clients", populate: { path: "loans", model: "loan"}}).exec(function(err, user){
if(err){
console.log(err);
} else{
var amountRepaid = calcRepaid(user.clients.loans);
console.log(user.clients.loans);
res.render("index", {clients: user.clients, amountRepaid: amountRepaid});
}
});
However it doesn't seem to work, my models are listed below and any help is appreciated!
models:
Client:
var mongoose = require("mongoose");
var clientSchema = mongoose.Schema({
loans: [{
type: mongoose.Schema.Types.ObjectId,
ref: "loan"
}],
emailAdderess: String,
firstname: String,
lastname: String,
contactNumber: String ,
dateCreated: {type: Date, default: Date.now},
gender: String,
})
module.exports = mongoose.model("Client", clientSchema);
User:
const mongoose = require("mongoose");
const passportLocalMongoose = require("passport-local-mongoose");
var UserSchema = mongoose.Schema({
username: String,
password: String,
firstname: String,
lastname: String,
clients: [{
type: mongoose.Schema.Types.ObjectId,
ref: "Client"
}]
});
UserSchema.plugin(passportLocalMongoose);
module.exports = mongoose.model("User", UserSchema);
Loan:
var mongoose = require("mongoose");
var LoanSchema = mongoose.Schema({
firstName: String,
lastName: String,
email: String,
contactNumber: Number,
amountBorrowed: Number,
length: String,
address: String,
dateDue: Date,
gender: String,
date: { type: Date, default: Date.now },
amountRepaid: { type: Number, default: 0},
loanRepaid: {type: Boolean, default: false}
})
module.exports = mongoose.model("loan", LoanSchema);

Answer 1

Try this:
.populate({
path: 'clients',
populate: {
path: 'clients.loans'
}
})