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(); }