public bool Save(CourseAssignToTeacher courseAssign)
 {
     if (IsCourseAlreadyAssigned(courseAssign.Course_id))
     {
         throw new Exception("Course Already Assigned");
     }
     return courseAssignGateway.Save(courseAssign)>0;
 }
        public int Save(CourseAssignToTeacher courseAssign)
        {
            string query = "INSERT INTO t_course_assign_to_teacher VALUES( '" + courseAssign.Teacher_id + "', '" + courseAssign.Course_id + "')";
            aSqlConnection.Open();
            aSqlCommand = new SqlCommand(query, aSqlConnection);

            int rowAffected =  aSqlCommand.ExecuteNonQuery();
            aSqlConnection.Close();
            return rowAffected;
        }
        private void saveButton_Click(object sender, EventArgs e)
        {
            try
            {
                CourseAssignToTeacher courseAssignToTeacher=new CourseAssignToTeacher();
                courseAssignToTeacher.Teacher_id = (int) teacherComboBox.SelectedValue;
                courseAssignToTeacher.Course_id = (int) courseComboBox.SelectedValue;
                if (courseAssignManager.Save(courseAssignToTeacher))
                {
                    MessageBox.Show("Course Assigned to Teacher Successful");
                }
                else
                {
                    MessageBox.Show("Course Assigned to Teacher Failed");
                }
            }
            catch (Exception exception)
            {

                MessageBox.Show(exception.Message);
            }
        }