public ActionResult Edit(Alumnos a)
        {
            try
            {
                using (var db = new Cursos_CRUDEntities())
                {
                    Alumnos al2 = db.Alumnos.Find(a.id_alumno);
                    al2.Nombres   = a.Nombres;
                    al2.Apellidos = a.Apellidos;
                    al2.Sexo      = a.Sexo;
                    al2.Edad      = a.Edad;

                    db.SaveChanges();
                    return(RedirectToAction("Index"));
                }
            }
            catch (Exception)
            {
            }
            return(View());
        }
        public ActionResult Add(Alumnos a)
        {
            if (!ModelState.IsValid)
            {
                return(View());
            }

            try
            {
                using (var db = new Cursos_CRUDEntities())
                {
                    db.Alumnos.Add(a);
                    db.SaveChanges();
                    return(RedirectToAction("Index"));
                }
            }
            catch (Exception ex)
            {
                ModelState.AddModelError("Error al crear", ex);
                return(View());
            }
        }