private void btn_add_Click(object sender, EventArgs e)
{
var studentService = new StudentService(_unit, _unit);
var groupService = new GroupService(_unit, _unit);
var student = studentService.GetStudentById(_studentId);
var group = (Group)cmBox_group.SelectedItem;
studentService.AddGroupToStudent(group, _studentId);
groupService.AddStudentToGroup(student, group.Id);
_unit.Commit();
this.Close();
}
