ssh中怎么修改级联对象值

[泪的告白篇]

public String save(){
		
		if(id == null){
			
			model.setCreatetime(new Date());
		}
		
		System.out.println(model);
		employeeService.saveorupdate(model);
		return SUCCESS;
	}

jsp的页面代码

<s:select list="#request.departments" 
    		listKey="id" listValue="departname" name="department.id" label="Department"></s:select>

<class name="com.czf.ssh.entities.Employee" table="ssh_employees" >
	
	<id name="id" column="id" type="integer">
	<generator class="native"></generator>
	</id>
	<property name="lastname" column="lastname" type="string"/>
	
	<property name="email" column="email" type="string"></property>
	
	<property name="birth" column="birth" type="date"></property>
	
	<property name="createtime" column="createtime" type="date"></property>
	
	 <!-- 映射单向 n-1 的关联关系 -->
	<many-to-one name="department" class="com.czf.ssh.entities.Department" column="dept_id" cascade="all"></many-to-one>
</class>

这张是ssh_employee的表

这张是ssh_departmente的表

现在我怎么从jsp页面传参给dept_id 让它更新
求方法 各位大神