I am trying to develop a banking website where users can apply for a loan. A single user can apply for multiple types of loans. Before a user successfully applies for a loan , I check if the user exists or not then I check all the loans for which the user has applied. If the user has already applied for the same type of loan then he/she will not be allowed to apply again.

For example, if a user has already applied for a home loan, he/she won't be allowed to apply for a home loan again.

Here is my User schema:

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
    email:{
        type:String,
        required:true,
        unique:true
    },
    password:{
        type:String,
        required:true,
    },
    isAdmin:{
        type:Boolean,
        required:true
    },
    account:{
        type:mongoose.Schema.Types.ObjectId,
        ref:'Account',
        required:false
    },
    transactions:{
        type:mongoose.Schema.Types.ObjectId,
        ref:'Transaction'
    },
    loans:[
        {
            type:mongoose.Schema.Types.ObjectId,
            ref:'Loan'
        }
    ]
},{
    timestamps:true
});

const User = mongoose.model('User',userSchema);

module.exports = User;

Here is Loan Schema

const mongoose = require('mongoose');

const loanSchema = new mongoose.Schema({
    user:{
        type:mongoose.Schema.Types.ObjectId,
        ref:'User',
        required:true
    },
    amount:{
        type:Number,
        required:true,
    },
    account:{
        type:mongoose.Schema.Types.ObjectId,
        ref:'Account',
        required:true
    },
    loantype:{
        type:String,
        required:true
    }
},{
    timestamps:true
});

const Loan = mongoose.model('Loan',loanSchema);

module.exports = Loan;

Here is what I have tried to do:

module.exports.apply = async function(req,res){
    try{
        let user = await User.findById(req.body.user)
        .populate('account')
        .populate({
            path:'loans',
            populate:{
                path:'loantype'
            }
        });
        let loan = await user.loans.find({loantype:req.body.loantype});
        if(loan){
            req.flash('error','Not Allowed');
            return res.redirect('back');
        }
        req.flash('success','Applied Successfully'); 
        return res.redirect('back');
    }catch(err){
        console.log('Error',err);
        return res.redirect('back');
    }
}

But this is not working. Any help will be much appreciated. Thanks !