Mongoose schema "this" keyword returns undefined

Question

I have the following schema which has two fields:

-finalGrade is entered by user

-numericGrade is derived from finalGrade

The problem is: No matter which value from the finalGrade's enum I enter, the numericGrade will always be 164. As I tried to escape the value of this.finalGrade, I found out that it always return "undefined".

How do I get the correct value returned?

Thanks in advance!

(Referenced: https://mongoosejs.com/docs/defaults.html#default-functions-and-this )

EDIT 2: entirety of Schema updated

const mongoose = require('mongoose');

const Student = mongoose.model('Student');
const Course = mongoose.model('Course');

let enrolmentSchema = new mongoose.Schema({

        student: {
            type: Number, 
            min: 1000000000, 
            max: 9999999999, 
            required: [true, "missing studentID"],
            validate:{
                isAsync: true,
                validator: function(v, cb){
                    Student.find({studentID: v}, function(err,docs){
                        cb(docs.length != 0);
                    })
                },
                message: 'Student does not exist...'
            }

        },
        course: {type: String, minlength: 3, maxlength: 3, required: [true, "missing courseID"]},
        semester:{
            type: Number, 
            validate:
            {
                validator: function(v){
                    return Number.isInteger(v) && v>= 1 && v<= 8;
                },
            message: "semester must be an integral value from [1 to 8]"
            }
        },
        finalGrade: {
            type: String,
            enum: ['E', 'G', 'P', 'F', '']
        },

        numericGrade:{
            type: Number,
            default: function()
            {
                console.log(escape("This is finalGrade:" +this.finalGrade)); //debugging
                if(this.finalGrade==='E'){
                    return 5;
                }
                else if(this.finalGrade==='G'){
                    return 4;
                }
                else if(this.finalGrade==='P'){
                    return 3;
                }
                else if(this.finalGrade==='F'){
                    return 2;
                }
                else if(this.finalGrade===''){
                    return 1;
                }
                else return 164;
            }
        }

})
mongoose.model('Enrolment', enrolmentSchema);

EDIT: Added document creation code as requested:

function insertEnrolmentRecord(req,res){
    var enrolment = new Enrolment();
    enrolment.student = req.body.student;
    enrolment.course = req.body.course;
    enrolment.semester= req.body.semester;
    enrolment.finalGrade= req.body.finalGrade;
    enrolment.save((err,doc)=>{
        if(err) {
            console.log(err);
            res.redirect('/enrolment/add_failed')
        }
        else res.redirect('/enrolment');

   })
}

How do you try it? Creating a document or updating a document? — SuleymanSah, Nov 10 '19 at 17:03
Did you checked if req.body.finalGrade is not undefined? Please check console.log(req.body.finalGrade) — SuleymanSah, Nov 10 '19 at 17:21
It is correctly extracted. console.log("req.body.finalGrade is: "+ escape(req.body.finalGrade)); returned req.body.finalGrade is: F — Nguyễn Duy Thái Sơn, Nov 10 '19 at 17:43
Ok good, can you also add the all Enrolment schema code to the question? — SuleymanSah, Nov 10 '19 at 17:49
Please check my answer, and don't forget to mark it as answer if it works for you. — SuleymanSah, Nov 10 '19 at 18:04

score 0 · Accepted Answer · answered Nov 10 '19 at 18:01

For some reason default option seems not to work, when you create your enrolment document like that.

But it seems to work when you use the constructor form.

Try like this:

function insertEnrolmentRecord(req, res) {

  const { student, course, semester, finalGrade } = req.body;

  let enrolment = new Enrolment({ student, course, semester, finalGrade });

  console.log(enrolment.numericGrade); // even here it will work

  enrolment.save((err, doc) => {
    if (err) {
      console.log(err);
      res.redirect('/enrolment/add_failed')
    }
    else res.redirect('/enrolment');

  })
}

Mongoose schema "this" keyword returns undefined

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