private void BtnAdd_Click(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(TxtTitle.Text) && !string.IsNullOrEmpty(TxtID.Text) && comboBoxCredits.Text != null && comboBoxDepartments.Text != null && comboBoxInstructors.Text != null)
            {
                using (var db = new SchoolEntities())
                {
                    // converting id text to number
                    Int32.TryParse(TxtID.Text, out Int32 ID);

                    // converting department name to department id
                    var deptID = from o in db.Department
                                 where o.Name.Equals(comboBoxDepartments.SelectedItem.ToString())
                                 select o.DepartmentID;

                    Int32.TryParse(deptID.First().ToString(), out Int32 finalDeptID);


                    // converting credits from combobox selection to number
                    Int32.TryParse(comboBoxCredits.SelectedItem.ToString(), out Int32 credits);

                    var course = new Course {
                        CourseID = ID, Title = TxtTitle.Text, Credits = credits, DepartmentID = finalDeptID
                    };
                    db.Course.Add(course);

                    // course instructor part
                    // missing from model (?)
                    //var courseInstructor = db.


                    db.SaveChanges();
                    dataGridView1.DataSource = db.Course.ToList();
                }
                TxtID.ResetText();
                TxtTitle.ResetText();
                comboBoxCredits.SelectedItem     = null;
                comboBoxDepartments.SelectedItem = null;
                comboBoxInstructors.SelectedItem = null;
            }
        }