hibernate在地图的方法之一协会

【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！

这个着重具体解说一下！

比如，我们如今一个组(Group)和人(Person）

id	name
1	张三
2	李四

(person表)

id	name	p_id
1	財务组	1
2	財务组	2

(Group表)

由上表我们发现，是不是出现数据的反复？財务组在反复！

所以。在多对一的单向映射中，我们一般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。一个组里面能够有多个人！

id	name
1	財务组
2	开发组

(person表)

id	name	G_id
1	张三	1
2	李四	1

(Group表)

上面这样的关系才是正常的业务逻辑！

ok，以下来看我们的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測试一下！

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！