九、一对多

三、一对多

 

1.在Department里添加集合属性

private int id;

private String name;

private Set<Employee> emps;//表示这个部门所含有的员工

 

2.在Department.hbm.xml下添加映射

 

<set name="emps">

<key column="dept_id"></key>

 

<!--<one-to-many class="com.myz.domain.Employee"/> -->

<one-to-many class="Employee"/>

</set>

 

 

3.测试

//取出所有部门编号为1的员工

Department department= (Department) session.get(Department.class, 1);

Set<Employee> emps = department.getEmps();

for(Employee e:emps){

System.out.println(e.getName());

}

 

//添加

Department department= new Department();

department.setId(2);

department.setName("人事部");

 

Set<Employee> sets=new HashSet<Employee>();

Employee e1=new Employee();

e1.setName("李逵"); e1.setId(3);

Employee e2=new Employee();

e1.setName("武松"); e2.setId(4);

 

sets.add(e1);

sets.add(e2);

 

department.setEmps(sets);

 

session.save(department);

 

执行这段代码可能会报错，因为在保存department的时候，hibernate还没有保存sets和e1,e2等对象。

如果发生了异常，在Department.hbm.xml的一对多中添加级联保存即可

<set name="emps" cascade="save-update">

<key column="dept_id"></key>

<!--<one-to-many class="com.myz.domain.Employee"/> -->

<one-to-many class="Employee"/>

</set>