Get bean from select tag on jsp page

I use Spring, jsp and Hibernate in my project. I have two entities Employee and Department. Dapartment is a part of Employee and they have relationship one-to-many

    @Entity
    @Table(name = "employee")
    public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @OneToOne
    @JoinColumn(name = "dep_id")
    private Department department;

I create controller, DAO and jsp pages for view.

My problem: I want to update data of Employee in my jsp page. Before this I add Employee and list of departments in model

In controller:

 model.addAttribute("employee", employeeDao.find(id));
 model.addAttribute("departments", departmentDao.list());

In JSP:

<form method="post">
   <select value="${employee.department}">
     <c:forEach items="${departments}" var ="dep">
        <option value="${dep}">${dep.name}</option>
     </c:forEach>
</form>

In controller (post request)

@RequestMapping(value = "/{id}", method = RequestMethod.POST)
    public String updateEmployee(@PathVariable("id") long id, Employee employee) {
        employee.setId(id);
        employeeDao.update(employee);

        return "redirect:/employees";
    }

but value employee.department=null Why?

Of course, on jsp page in "select" tag I can create variable dep I mean:

<select name ="dep">
   <option value="${dep.id}">${dep.name}</option>
</select>

and then in controller using id of department i will be able to get department from database and update Employee. Is it right way?