Insert data into database(MVC) - asp.net-mvc

Question

I am trying to insert datas to Appointment table of my database. I did registration part of my project which works well. There are 2 tables, Patient and Appointment. After Login patients can make an appointment. Patient number comes like this
MyUser.PatientNo = Guid.NewGuid().GetHashCode();
For appointment date and description comes from textbox. And I want to insert PatientNo from Patient table to Appointment table. For me it looks done but when I choose date and write description but I got error on this line app.PatientNo = patient.PatientNo;
An exception of type 'System.NullReferenceException' occurred in DentAppSys.dll but was not handled in user code
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Make(Models.AppModel User)
{
if (Session["UserEmail"] != null)
{
using (var db = new MaindbModelDataContext())
{
var patient = db.Patients.FirstOrDefault(u => u.Email == (String)Session["UserEmail"]);
var app = new Appointment();
app.Date = User.Date;
app.Description = User.Description;
app.Status = "true";
app.PatientNo = patient.PatientNo;
db.Appointments.InsertOnSubmit(app);
db.SubmitChanges();
return RedirectToAction("Make", "Appointment");
}
}
else
{
return RedirectToAction("Index", "User");
}
}
}
}
and this is registration part which is working well
public ActionResult RegAndLogin(Models.RegAndLog User)
{
if (User.RegisterModel != null)
{
if (ModelState.IsValid)
{
using (var db = new MaindbModelDataContext())
{
var Person = db.Patients.FirstOrDefault(u => u.Email == User.RegisterModel.Email);
if (Person == null)
{
string Hash = BCrypt.Net.BCrypt.HashPassword(User.RegisterModel.Password);
var MyUser = new Patient();
MyUser.Name = User.RegisterModel.Firstname;
MyUser.Surname = User.RegisterModel.Lastname;
MyUser.Birthday = User.RegisterModel.Birthday;
MyUser.Email = User.RegisterModel.Email;
MyUser.Password = Hash;
MyUser.PatientNo = Guid.NewGuid().GetHashCode();
db.Patients.InsertOnSubmit(MyUser);
db.SubmitChanges();
Session["UserEmail"] = User.RegisterModel.Email;
return RedirectToAction("Index", "Patient", User.RegisterModel);
}
else
{
ModelState.AddModelError("", "There is a user with this Email. Please enter another Email !!!");
return View();
}
}
}
else
{
ModelState.AddModelError("", "Data is incorrect !!!");
}
}
else
{
if (ModelState.IsValid && IsValid(User.LoginModel.Email, User.LoginModel.Password))
{
var TempUser = new Models.RegisterModel();
Session["UserEmail"] = User.LoginModel.Email;
using (var db = new MaindbModelDataContext())
{
var person = db.Patients.FirstOrDefault(u => u.Email == User.LoginModel.Email);
TempUser.Firstname = person.Name;
TempUser.Lastname = person.Surname;
//TempUser.RegisterModel.Birthday = (DateTime)person.BirthDate;
TempUser.Email = person.Email;
}
return RedirectToAction("Index", "Patient", TempUser);
}
else
{
ModelState.AddModelError("", "Check your E-mail or Password then try again !!!");
}
}
return View();

Answer 1

If you're getting a null exception on the line
app.PatientNo = patient.PatientNo;
It will be because either app or patient are null at when it's executed. I would suspect patient.
Check that patient is found correctly at the line
var patient = db.Patients.FirstOrDefault(u => u.Email == (String)Session["UserEmail"]);
if it isn't found patient will be null.