Nodejs和mongoose，迭代数据库以创建一个新的

Question

I have a collection with unordered student exams with this mongoose model:

var ExamSchema = new Schema({
  firstName: String,
  lastName: String,
  studentCode: String,
  examType: String,
  examDate: String,
  examResult: String
});

I need to create a new collection grouping exams based on student's code as in this model:

var StudentSchema = new Schema({
  firstName: String,
  lastName: String,
  studentCode: String,
  test: [{
    type: String,
    date: String,
    result: String
  }]
});

I tried this function but it just inserts all the students and never finds the student code.

function rebuildDb(err, done) {
 Exam.find({} , function(err, doc) {
  if(err) return err;
  doc.map( function(exam) {
        Student.findOne({ studentCode: exam.studentCode }, function(err, foundExam) {
         if(err) return callback(err);
         if(foundExam == null) {
           var student = new Student ({
             firstName: exam.firstName,
             lastName: exam.lastName,
             studentCode: exam.studentCode,
             test: [{
                type: exam.examType,
                date: exam.examDate,
                result: exam.examResult
              }],
           });
             student.save(function(err, newStudent) {
             if(err) return err;
             console.log("New student created: " + student.studentCode);
           });
         } else {
           Student.update({ studentCode: exam.studentCode }, { "$push": {
              test: {
                type: exam.examType,
                date: exam.examDate,
                result: exam.examResult
              }
            } }, function(err, newTest) {
           if(err) return err;
           console.log("New test for student: " + student.studentCode);
           });
         }
     });
  });
});
};

I think it is a sync/async issue, but I don't know how to handle it. What's the best practice in a case like this?

Thanks in advance.

Answer 1

Try this

const saveStudent = (exam) => {
    return new Promise((resolve, reject) => {
        const student = new Student({
            firstName: exam.firstName,
            lastName: exam.lastName,
            code: exam.code,
            test: [{
                type: exam.examType,
                date: exam.examDate,
                result: exam.examResult
            }],
        });
        student.save(function (err, newStudent) {
            if (err) return reject(err);
            console.log("New student created: " + student.code);
            resolve(newStudent);
        });
    });
}

const updateStudent = (exam) => {
    return new Promise((resolve, reject) => {
        Student.update({
            code: exam.code
        }, {
            "$push": {
                test: {
                    type: exam.examType,
                    date: exam.examDate,
                    result: exam.examResult
                }
            }
        }, function (err, newTest) {
            if (err) return reject(err);
            console.log("New test for student: " + student.code);
            resolve(newTest);
        });
    });
}

const findExam = async () => {
    const doc = await Exam.find({}).exec();
    doc.forEach(exam => {
        const foundExam = await Student.findOne({
            code: exam.code
        }).exec();
        if (foundExam == null) {
            await saveStudent(exam);
        } else {
            await updateStudent(exam);
        }
    });
}