在项目的开发中多对一的单向关联映射是最常见的，关联映射！这个着重详细讲解一下！
例如，我们现在一个组(Group)和人(Person）
(Person表)
| id | name |
| 1 | 张三 |
| 2 | 李四 |
（Group表）
| id | name | p_id |
| 1 |
财务组 | 1 |
| 2 | 财务组 | 2 |
由上表我们发现，是不是出现数据的重复？财务组在重复！
所以，在多对一的单向映射中，我们通常是在多的一方加上外键来关联少的一方。
那么在这个关系中(Group)是少的一方，(Person)是多的一方，一个组里面可以有多个人！
(Group表)
| id | name |
| 1 | 财务组 |
| 2 | 开发组 |
（Person表）
| id | name | g_id |
| 1 |
张三 | 1 |
| 2 | 李四 | 1 |
上面这种关系才是正常的业务逻辑！
ok，下面来看我们的Annotations配置！
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@Entity
@Table
(name=
"t_user"
)
publicclass Person {
private
Integer id;
private
String name;
private
Integer age;
private
Group group;
@ManyToOne
public
Group getGroup() {
returngroup;
}
publicvoid setGroup(Groupgroup) {
this
.group = group;
}
@Id
@GeneratedValue
public
Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this
.id = id;
}
@Column
(name=
"name"
)
public
String getName() {
returnname;
}
publicvoid setName(Stringname) {
this
.name = name;
}
@Column
(name=
"age"
)
public
Integer getAge() {
returnage;
}
publicvoid setAge(Integerage) {
this
.age = age;
}
}
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@Entity
@Table
(name=
"t_group"
)
publicclass Group {
private
Integer id;
private
String name;
@Id
@GeneratedValue
public
Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this
.id = id;
}
@Column
(name=
"name"
)
public
String getName() {
returnname;
}
publicvoid setName(Stringname) {
this
.name = name;
}
}
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XML配置方法
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package
csg.hibernate.entity;
publicclass Person {
private
Integer id;
private
String name;
private
Integer age;
private
Group group;
public
Group getGroup() {
returngroup;
}
publicvoid setGroup(Groupgroup) {
this
.group = group;
}
public
Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this
.id = id;
}
public
String getName() {
returnname;
}
publicvoid setName(Stringname) {
this
.name = name;
}
public
Integer getAge() {
returnage;
}
publicvoid setAge(Integerage) {
this
.age = age;
}
}
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package
csg.hibernate.entity;
publicclass Group {
private
Integer id;
private
String name;
public
Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this
.id = id;
}
public
String getName() {
returnname;
}
publicvoid setName(Stringname) {
this
.name = name;
}
}
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<?
xml
version
=
"1.0"
?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<
hibernate-mapping
package
=
"csg.hibernate.entity"
>
<
class
name
=
"Person"
table
=
"t_user"
>
<
id
name
=
"id"
>
<
generator
class
=
"native"
/>
</
id
>
<
property
name
=
"name"
/>
<
property
name
=
"age"
/>
<
many-to-one
name
=
"Group"
column
=
"group_id"
/>
</
class
>
</
hibernate-mapping
>
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<?
xml
version
=
"1.0"
?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<
hibernate-mapping
package
=
"csg.hibernate.entity"
>
<
class
name
=
"Group"
table
=
"t_group"
>
<
id
name
=
"id"
>
<
generator
class
=
"native"
/>
</
id
>
<
property
name
=
"name"
/>
</
class
>
</
hibernate-mapping
>
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到这里我们使用Junit测试一下
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publicclass JuniTest {
privatestatic SessionFactory sessionFactory;
@BeforeClass
publicstaticvoid beforeClass() {
Configuration cfg=
new
Configuration();
cfg.configure();
sessionFactory=cfg.buildSessionFactory();
}
@Test
public
void
add(){
try
{
Group group=
new
Group();
Session session = sessionFactory.getCurrentSession();
session.beginTransaction();
group.setName(
"部门"
);
session.save(group);
Person person=
new
Person();
person.setAge(
12
);
person.setName(
"张三"
);
person.setGroup(group);
session.save(person);
session.getTransaction().commit();
}
catch
(HibernateException e){
e.printStackTrace();
}
}
@AfterClass
publicstaticvoid afterClass() {
sessionFactory.close();
}
}
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ok！
本文转自 小夜的传说 51CTO博客，原文链接：http://blog.51cto.com/1936625305/1568855，如需转载请自行联系原作者
