How to properly use references in mongoose - node.js

Question

I am trying to use references in mongoose but somehow am not being able to do it properly.
What I am trying to achieve
I would like to query the examModel and get all information about a particular exam including the questions related to that exam.
What I achieved
New questions get saved into the questionModel with the object id of the exam am saving the question for, BUT, the questions array of the examModel doesnt take notice of it.
I have two different models:
examModel
const examSchema = new mongoose.Schema({
examId: {
type: String,
unique: true,
index: true,
required: true,
default: _generateAlphanumericId(18),
},
questions: [{
type: mongoose.Schema.Types.ObjectId,
ref: "Questions",
}],
}, {
timestamps: true,
});
module.exports = mongoose.model("Exams", examSchema);
questionModel
const questionSchema = new mongoose.Schema({
_refExamId: {
type: mongoose.Schema.Types.ObjectId,
ref: "Exams",
},
questionId: {
type: String,
unique: true,
index: true,
required: true,
default: _generateAlphanumericId(26),
},
title: {
type: String,
trim: true,
required: [true, "Question is missing"],
},
}, {
timestamps: true,
});
module.exports = mongoose.model("Questions", questionSchema);
Now, when I save a new question into the question model, I am sending the _id of an exam from the exam model but still the questions array of exam model doesnt save the object ids of newly created questions.
How I am creating a new question
try {
const question = new questionModel({ _refExamId: req.body._refExamId, title: req.body.title });
await question.save();
return res.status(200).json({ type: "SUCCESS" });
}
catch (error) {
return res.status(500).json({
type: "ERROR",
message: "Some unknown error occurred",
});
}

Answer 1

try {
const question = new questionModel({ _refExamId: req.body._refExamId, title: req.body.title });
const saved_question = await question.save();
const getExam = await examModel.find({_id: saved_question._refExamId});
getExam.questions.push(saved_question._id);
const result = await getExam.save();
return res.status(200).json({ type: "SUCCESS" });
}catch (error) {
return res.status(500).json({
type: "ERROR",
message: "Some unknown error occurred",
});
}
This should get it working.

Answer 2

First of all,
Exam Model
const examSchema = new mongoose.Schema({
examId: {
type: String,
unique: true,
index: true,
required: true,
default: _generateAlphanumericId(18),
},
questions: [{
type: mongoose.Schema.Types.ObjectId,
ref: 'Question'
}],
}, {
timestamps: true,
});
module.exports = mongoose.model("Exam", examSchema);
Note: I turned Exams to Exam, Mongodb will change it to plural on your DB
Question Model
const questionSchema = new mongoose.Schema({
_refExamId: {
type: mongoose.Schema.Types.ObjectId,
ref: "Exam",
},
questionId: {
type: String,
unique: true,
index: true,
required: true,
default: _generateAlphanumericId(26),
},
title: {
type: String,
trim: true,
required: [true, "Question is missing"],
},
}, {
timestamps: true,
});
module.exports = mongoose.model("Question", questionSchema);
Note: I turned Questions to Question, Mongodb will change it to plural on your DB
Creating a new Question
try {
const question = new questionModel({ _refExamId: req.body._refExamId, title: req.body.title });
await question.save();
return res.status(200).json({ type: "SUCCESS" });
}
catch (error) {
return res.status(500).json({
type: "ERROR",
message: "Some unknown error occurred",
});
}
Try that and lets see

Answer 3

So, I was not reading the refs-to-children part of the docs where it states that, there will be no references in the parent schema unless we explicitly push the reference to the parent.
As a result the following solved my issue:
try {
const exam = await examModel.findOne({ examId: req.body.exam_id });
const question = new questionModel({ title: req.body.title, positiveMarks: req.body.positiveMarks });
exam.questions.push(question);
await exam.save(question.save());
return res.status(200).json({ type: "SUCCESS" });
}
catch (error) {
return res.status(500).json({
type: "ERROR",
message: "Some unknown error occurred",
});
}