Node.js 在引用文档中插入数据？

我正在尝试将数据插入myMongoDB数据库，我使用的是引用文档，但我找不到任何方便的方法来插入数据（而获取非常方便）。
请在标记副本之前阅读，我在发布之前已经搜索了整个Stackoverflow和github
这是我的考试模式

const ExamSchema = new mongoose.Schema({
    name: {},
    description: {},
    allowedTime: {},
    subject: {},
    assignedInCharge: {},
    questions: [{ type: mongoose.Schema.Types.ObjectId, ref: 'MCQuestion' }]
});

下面是我的问题模式：

const MultipleChoiceQuestionSchema = new mongoose.Schema({
    question: {},
    answerOptions: [{}],
    correctAnswer: {},
    marksForCorrectAnswer: {},
    negativeMark: {},
    difficulty: {}
});

我的问题是：mongoose中是否有内置方法将文档中缺少的数据放入数据库中（我已经在那里搜索了一千次）。

我的输入如下：

{
    "name": "Sample Exam 1",
    "description": "IDK if this will work",
    "allowedTime": 123445666,
    "subject": "testsub1",
    "assignedInCharge": "someincharge",
    "questions": [
        {
            "question": "this is que1",
            "answerOptions": ["this is op 1", "this is op 2", "op 3", "op 4"],
            "correctAnswer": "this is op 1",
            "marksForCorrectAnswer": 4,
            "negativeMark": 1,
            "difficulty": 3
        },
        {}, {}, {}
    ]
}

（很抱歉有这么长的代码片段）我尝试将数据插入数据库的方法是：

router.post('/admin/createExam', (request, response) => {

    questions = request.body.questions;
    var idarray = [];

    questions.forEach(function(element) {
        var question = new MCQuestion(element);
        question.save().then((doc) => idarray.push(doc._id), (error) => console.log(error));
    });

    var body = _.pick(request.body, ['Everything Except Questions']);
    body.questions = idarray;

    var exam = new Exam(body);  

    exam.save().then(() =>{
        response.send(exam);
    }).catch((error) => {
        response.status(400).send(error);
    });

});

我能够成功地将问题保存到问题集合中，但未正确保存考试集合

---

请帮帮我，我已经在这上面花了好几个星期的时间了。

没关系，我明白了，改变API方法使它变得很好

router.post('/admin/createExam', (request, response) => {

    var body = _.pick(request.body, ['name', 'description', 'allowedTime', 'subject', 'assignedInCharge']);
    var exam = new Exam(body);

    request.body.questions.forEach(function(element) {
        element.exam = exam._id;
        var question = new MCQuestion(element);
        exam.questions.push(question._id);
        question.save().catch((error) => console.log(error));
    });

    exam.save().then(() =>{
        response.send(exam);
    }).catch((error) => response.status(400).send(error));

});

---

没关系，我明白了，改变API方法使它变得很好

router.post('/admin/createExam', (request, response) => {

    var body = _.pick(request.body, ['name', 'description', 'allowedTime', 'subject', 'assignedInCharge']);
    var exam = new Exam(body);

    request.body.questions.forEach(function(element) {
        element.exam = exam._id;
        var question = new MCQuestion(element);
        exam.questions.push(question._id);
        question.save().catch((error) => console.log(error));
    });

    exam.save().then(() =>{
        response.send(exam);
    }).catch((error) => response.status(400).send(error));

});