【Hibernate】之关于多对一单向关联映射
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！
@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;
}
}
@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;
}
}
XML配置方法
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;
}
}
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;
}
}
<?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>
<?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>
到这里我们使用Junit测试一下
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();
}
}
ok！
时间： 2024-10-03 21:53:19