public Teacher[] GetAggregatedTeachers()
        {
            string[] allTeachers = _teachersRepository.SelectAllTeachers();

            Teacher[] teachers = _teachersRepository.SelectAggregatedTeachers();

            List <Teacher> result = new List <Teacher>();

            foreach (var teacherName in allTeachers)
            {
                Teacher teacher = teachers.FirstOrDefault(t => t.Name == teacherName);

                if (teacher != null)
                {
                    result.Add(teacher);
                }
                else
                {
                    result.Add(new Teacher(teacherName));
                }
            }

            return(result.ToArray());
        }