private void buttonAddCourse_Click(object sender, EventArgs e)
        {
            string         courseName      = textBoxCourseName.Text;
            string         teacherselected = this.comboBox1.GetItemText(this.comboBox1.SelectedItem);
            int            teacherid       = 0;
            int            groupid         = 0;
            int            courseid        = 0;
            List <Teacher> teacherlist     = duombaze.GetTeacher();

            foreach (Teacher teacher in teacherlist)
            {
                if (teacherselected == teacher.Name + " " + teacher.Surname)
                {
                    teacherid = teacher.Id;
                }
            }
            duombaze.AddNewCourse(courseName, teacherid);
            string       groupselected = this.comboBox2.GetItemText(this.comboBox2.SelectedItem);
            List <Group> grouplist     = duombaze.GetGroup();

            foreach (Group group in grouplist)
            {
                if (groupselected == group.GroupName)
                {
                    groupid = group.Id;
                }
            }
            List <Course> courselist = duombaze.GetCourse();

            foreach (Course course in courselist)
            {
                if (courseName == course.Name)
                {
                    courseid = course.Id;
                }
            }
            duombaze.AddNewLesson(teacherid, groupid, courseid);


            this.Close();
        }