record

function insertCourseRecord(req,res){
    var course = new Course();
    course.courseID = req.body.courseID.toUpperCase();
    course.courseName = req.body.courseName;
    course.prerequisites= req.body.prerequisites.toUpperCase();
    if(req.body.prerequisites.toUpperCase().length){
        Course.find({courseID: req.body.prerequisites.toUpperCase()}).exec(function(err, c_docs){
            if(err){
                res.redirect('/course/operation_failed?err='+ err.message);
            }
            else if(!c_docs.length){
                res.redirect('/course/operation_failed?err=prerequisites:%20not%20a%20valid%20prerequisites%20'
                    +'(does%20not%20exist%20such%20course%20in%20DB)')
            }
            else{
                course.save((error,doc)=>{
                if(error) {
                    res.redirect('/course/operation_failed?err='+ err.message)
                }
                else res.redirect('/course?status=Add%20course%20with%20ID%20'
                    + req.body.courseID.toUpperCase() + '%20succeeded.');

                })
            }
        })
    }
    else{
        course.save((err,doc)=>{
        if(err) {
            res.redirect('/course/operation_failed?err='+ err.message)
        }
        else res.redirect('/course?status=Add%20course%20with%20ID%20'
            + req.body.courseID.toUpperCase() + '%20succeeded.');
        })
    }
}

router.post('/update/', function updateCourseRecord(req,res){
    //check prerequisites
    var update = Course.findByIdAndUpdate(req.body._id,
    {
        courseName : req.body.courseName,
        prerequisites: req.body.prerequisites.toUpperCase()
    }, {new: true, runValidators: true})

    if(req.body.prerequisites.toUpperCase().length){
        Course.find({courseID: req.body.prerequisites.toUpperCase()}).exec(function(err, c_docs){
            if(err){
                res.redirect('/course/operation_failed?err='+ err.message);
            }
            else if(!c_docs.length){ //throwing 'ERR_HTTP_HEADERS_SENT'
                console.log("This is if else if block")
                res.redirect('/course/operation_failed?err=prerequisites:%20not%20a%20valid%20prerequisites%20'
                    +'(does%20not%20exist%20such%20course%20in%20DB)' )
            }
            else{
                update.exec(function(error,data){
                    if(error){
                        console.log("In course update failed by: "+ err.message);
                        res.redirect('/course/operation_failed?err='+ err.message);
                    }
                    else {
                        console.log("if else else ran");
                        res.redirect('/course?status=Update%20course%20'
                        + req.body.courseName+ '%20succeeded.');
                    }
                })
            }
        })
    }
    else
    {
        update.exec(function(err,data){
        if(err){
            console.log("In course update failed by: "+ err.message);
            res.redirect('/course/operation_failed?err='+ err.message);
        }
        else res.redirect('/course?status=Update%20course%20'
            + req.body.courseName+ '%20succeeded.');
        })
    }


    update.exec(function(err,data){
        if(err){
            console.log("In course update failed by: "+ err.message);
            res.redirect('/course/operation_failed?err='+ err.message);
        }
        else res.redirect('/course?status=Update%20course%20'
            + req.body.courseName+ '%20succeeded.');
    })
})

router.get('/operation_failed',(req,res)=>{
        res.render('course/modifyCourseFailed',
        {
            errorMessage: req.query.err,
            style: 'student.css'
        }
    )
})