Problem in Updating Using Entity Framework

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C#

I was going through the examples of http://entityframeworktutorial.net/[^]

here in updating the one to many case my a new standard is added to my Standard table instead of updating the old one. Also in teachers table new teacher is added with standard id of the newly created standard. here is my code ...

Standard std = null;

using (SchoolDBEntities ent = new SchoolDBEntities())
{
    ent.ContextOptions.LazyLoadingEnabled = false;
    std = (from s in ent.Standards.Include("Teachers") where s.StandardName == "Standard2" select s).FirstOrDefault<Standard>();
}

std.StandardName = "UpdatedStandard";
std.Description = "Updated Class";

if (std.Teachers != null)
{
    if (std.Teachers.Count >= 2)
    {
        Teacher updtTeacher = std.Teachers.ElementAt<Teacher>(0);



        Teacher delTeacher = std.Teachers.ElementAt<Teacher>(1);

        std.Teachers.Remove(delTeacher);
        std.Teachers.Remove(updtTeacher);

        updtTeacher.TeacherName = "UpdatedTeacher";
        std.Teachers.Add(updtTeacher);
    }
}
Teacher newTeacher = new Teacher();
newTeacher.TeacherName = "NewTeacher";
std.Teachers.Add(newTeacher);

using (SchoolDBEntities ent = new SchoolDBEntities())
{


    var existingStandard = (from s in ent.Standards where s.StandardId == std.StandardId select s).FirstOrDefault<Standard>();

    var existingTeachers = existingStandard.Teachers.ToList<Teacher>();
    var newTeachers = std.Teachers.ToList<Teacher>();

    var addedTeachers = newTeachers.Except(existingTeachers, tchr => tchr.TeacherId);
    var deletedTeachers = existingTeachers.Except(newTeachers, tchr => tchr.TeacherId);
    var updatedTeachers = existingTeachers.Except(deletedTeachers, tchr => tchr.TeacherId);

    //foreach(Teacher t in addedTeachers.ToList<Teacher>())
    //{
    //    ent.Teachers.AddObject(t);
    //}

    addedTeachers.ToList<Teacher>().ForEach(t => ent.Teachers.AddObject(t));


    foreach (Teacher t in updatedTeachers)
    {
        ent.Teachers.Attach(t);
        ent.ObjectStateManager.ChangeObjectState(t, System.Data.EntityState.Modified);

    }

    foreach (Teacher t in deletedTeachers)
    {
        ent.Teachers.DeleteObject(t);

    }

    ent.SaveChanges();

}

somebody please help