public ActionResult New(NewEnrollmentViewModel form)
        {
            if (!ModelState.IsValid)
            {
                return View(form);
            }

            var user = _context.Users.Single(u => u.Id == form.UserId);

            var cohortId = Convert.ToInt32(form.CohortId);
            var cohort = _context.Cohorts.Single(c => c.Id == cohortId);

            EnrollmentServices.CreateNewEnrollment(cohort, user, _context);
            return null;

        }
 public ActionResult New()
 {
     var form = new NewEnrollmentViewModel();
     return View(form);
 }