private void Form1_Load(object sender, EventArgs e)
        {
            SchoolEntities entities = new SchoolEntities();
            entities.Class.ToList();
            List<Student> listStudent = entities.Student.ToList();

            List<ItemOfGrid> listToFill = new List<ItemOfGrid>();
            foreach (var student in listStudent)
            {
                listToFill.Add(new ItemOfGrid(student.Name,
student.Class.ClassName));
            }
            dataGridView1.DataSource = listToFill;
        }