Hibernate one to one映射关系

在数据库中，表和表之间的关系有：一对一，一对多和多对多。

通过Hibernate，我们可以把实体对象直接映射到数据库中，完成建表。

今天我要总结的是在Hibernate 中实现一对一映射关系，其中一对一分为外键关联和主键关联。

一、外键关联

1.先创建 2个实体类

public class Student {
private Integer id;
private String stuname;
private int password;
private Date birthday;
private Phone phone;

public Student() {
}

public Student(String stuname, int password, Date birthday) {
this.stuname = stuname;
this.password = password;
this.birthday = birthday;
}

public Phone getPhone() {
return phone;
}

public void setPhone(Phone phone) {
this.phone = phone;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getStuname() {
return stuname;
}

public void setStuname(String stuname) {
this.stuname = stuname;
}

public int getPassword() {
return password;
}

public void setPassword(int password) {
this.password = password;
}

public Date getBirthday() {
return birthday;
}

public void setBirthday(Date birthday) {
this.birthday = birthday;
}

@Override
public String toString() {
return "Student [id=" + id + ", stuName=" + stuname + ", password=" + password + ", birthday=" + birthday + "]";
}

}

public class Phone {
private Integer id;
private String telephone;
private String homephone;

private Student stu;

public Student getStu() {
return stu;
}

public void setStu(Student stu) {
this.stu = stu;
}

public Phone() {

}

public Phone(String telephone, String homephone) {
super();
this.telephone = telephone;
this.homephone = homephone;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getTelephone() {
return telephone;
}

public void setTelephone(String telephone) {
this.telephone = telephone;
}

public String getHomephone() {
return homephone;
}

public void setHomephone(String homephone) {
this.homephone = homephone;
}

@Override
public String toString() {
return "Phone [id=" + id + ", telephone=" + telephone + ", homephone=" + homephone + "]";
}

}

我们要做的就是让student和phone表形成一对一的关系。

2.hibernate.cfg.xml文件配置

cfg文件用来配置连接数据库相关属性

<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory>
<!-- 指定方言，更好的操作数据库，因为数据库都有一些区别，通过方言的设置可以对应使用目标数据库的特点支持事务的MySQL5InnoDBDialect用于5.5之后。 -->
<property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql:///hiber</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
<!--
数据库自动创建表操作
#hibernate.hbm2ddl.auto create-drop 程序启动时创建数据库表，程序退出时删除之前创建的
#hibernate.hbm2ddl.auto create      程序启动时删除上一次创建的表，然后再创建新的表结果
#hibernate.hbm2ddl.auto update      程序启动时如果没有表就创建表，有就检查有没有更新（推荐）
#hibernate.hbm2ddl.auto validate    程序启动是检查表结构，不会创建
-->
<property name="hibernate.hbm2ddl.auto">update</property>
<!-- 显示执行的sql语句 -->
<property name="show_sql">true</property>
<!-- 格式化显示执行的sql语句 -->
<property name="hibernate.format_sql">false</property>
<!-- 引入需要持久化的映射文件配置文件 -->
<mapping resource="entity/Student.hbm.xml"/>
<!-- <mapping resource="entity/Phone.hbm.xml"/> -->
</session-factory>
</hibernate-configuration>

3.只配置student.hbm.xml映射文件

在这里我把phone和student的映射整合在一起，即把phone的映射配置写在student.hbm.xml中，所以只需要一个xml。（此xml文件放在实体类所在包中）

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="entity" >
<class name="Student" >
<id name="id" >
<generator class="native"></generator>
</id>
<property name="stuname" ></property>
<property name="password" ></property>
<property name="birthday" ></property>

<!-- 级联操作 student和phone关联-->
<one-to-one name="phone" cascade="all" />
</class>
<!--配置phone的映射-->
<class name="Phone" >
<id name="id" >
<generator class="native"></generator>
</id>
<property name="telephone" ></property>
<property name="homephone" ></property>
<!--many代表外键关联-->
<many-to-one name="stu" column="stu_id" unique="true" not-null="true"></many-to-one>
</class>
</hibernate-mapping>

4 . 测试类

public class TestHiber {
SessionFactory factory = null;
Session session = null;

@Before
public void setUp() throws Exception {
Configuration config = new Configuration().configure();
ServiceRegistry sr = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
factory = config.buildSessionFactory(sr);
session = factory.openSession();
}

@After
public void tearDown() throws Exception {
if(session != null){
if(session.isOpen()){
session.close();
}
}
}

/*
* 新增
*/
@Test
public void testsave1() {
Transaction tx = session.beginTransaction();

Student stu = new Student("zhangsan", 123456, new Date());
Phone p = new Phone("110", "119");

stu.setPhone(p);
p.setStu(stu);

session.save(stu);
session.save(p);

tx.commit();
}

进入mysql可以看到2张表已经建好，如图：



stu-id是phone的外键，关联student

-

二、主键关联

只需修改student.hbm.xml配置即可

<hibernate-mapping  >
<class name="entity.Student" >
<id name="id" >
<generator class="native"></generator>
</id>
<property name="stuname" ></property>
<property name="password" ></property>
<property name="birthday" ></property>

<!-- 级联操作 -->
<one-to-one name="phone" cascade="all"></one-to-one>
</class>

<class name="entity.Phone"  >
<id name="id" >
<!-- 从表的id不由自己生成，而且必须和主表保持一致 -->
<generator class="foreign">
<!-- 指定从表的id来源 ，值为phone中指定的属性名-->
<param name="property">stu</param>
</generator>
</id>
<property name="telephone" ></property>
<property name="homephone" ></property>
<!-- 设置约束管理 -->
<one-to-one name="stu" constrained="true"></one-to-one>
</class>
</hibernate-mapping>

进入mysql 效果如图



采用主键关联的方法就没用外键关联的stu-id了。