hibernate之关于使用连接表实现多对一关联映射

【Hibernate】之关于使用连接表实现多对一关联映射

在我们项目使用中採用中间表最多的一般就是多对一,或者是多对多，当然一对一使用中间表也是能够的，可是这样的几率通常少之又少！所以这里重点介绍多对一和一对多的採用中间表进行关联映射！

依旧採用Group和Person来描写叙述这个逻辑！

Annotations配置

@Entity
@Table(name="t_group")
publicclass Group {
private Integer id;
private String name;
@Id
@GeneratedValue
public Integer getId() {
returnid;
}
publicvoid setId(Integer id) {
this.id = id;
}
@Column(name="g_name")
public String getName() {
returnname;
}
publicvoid setName(String name) {
this.name = name;
}
}

@Entity
@Table(name="p_person")
publicclass Person {
private Integer id;
private String name;
private Integer age;
private Group group;
@ManyToOne

//以下是配置中间表的核心
@JoinTable(name="g_p",joinColumns={@JoinColumn(name="p_id")},
inverseJoinColumns={@JoinColumn(name="g_id")})
public Group getGroup() {
returngroup;
}
publicvoid setGroup(Group group) {
this.group = group;
}
@Id
@GeneratedValue
public Integer getId() {
returnid;
}
publicvoid setId(Integer id) {
this.id = id;
}
@Column(name="p_name")
public String getName() {
returnname;
}
publicvoid setName(String name) {
this.name = name;
}
@Column(name="p_age")
public Integer getAge() {
returnage;
}
publicvoid setAge(Integer age) {
this.age = age;
}
}

XML配置

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/HibernateMapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="csg.hibernate.entity">
<class name="Person" table="t_person">
<id name="id">
<column name="id"/>
<generator class="native" />
</id>
<property name="name" />
<property name="age" />
<join table="t_p" optional="true">
<key column="p_id"></key>
<many-to-one name="group" column="g_id" class="Group" unique="true"/>
</join>
</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/HibernateMapping 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">
<column name="id"/>
<generator class="native" />
</id>
<property name="name" />
</class>
</hibernate-mapping>

写这篇文章，我特意查询了一下网上的文章，发现大家都是採用XML配置的，所以我这里也写了Annotations配置，由于JPA中的Annotations使用起来远比XML要方便！OK?

XML配置