[SXT][WY]Hibernate05 多对一及一对一关联映射

many-to-one

 

Group.hbm.xml
<?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>
 <class name="com.bjsxt.hibernate.Group" table="t_group">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="name"/>
 </class>
</hibernate-mapping>

User.hbm.xml
<?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>
 <class name="com.bjsxt.hibernate.User" table="t_user">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="name"/>
  <!--
  <many-to-one name="group" column="groupid" cascade="all"/>
   -->
   <many-to-one name="group" column="groupid"/>
 </class>
</hibernate-mapping>

public void testSave1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   Group group = new Group();
   group.setName("尚学堂");
   
   User user1 = new User();
   user1.setName("菜10");
   user1.setGroup(group);
   
   User user2 = new User();
   user2.setName("容祖儿");
   user2.setGroup(group);
   
   //不能成功保存，抛出TransientObjectException异常
   //因为Group为Tran sient状态，oid没有分配值
   //persistent状态的对象是不能引用transient状态的对象的
   session.save(user1);
   session.save(user2);
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }

public void testSave2() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   Group group = new Group();
   group.setName("尚学堂");
   
   session.save(group);
   
   User user1 = new User();
   user1.setName("菜10");
   user1.setGroup(group);
   
   User user2 = new User();
   user2.setName("容祖儿");
   user2.setGroup(group);
   
   //可以正确存储
   session.save(user1);
   session.save(user2);
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 

public void testSave3() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   Group group = new Group();
   group.setName("尚学堂");
   
   User user1 = new User();
   user1.setName("菜10");
   user1.setGroup(group);
   
   User user2 = new User();
   user2.setName("容祖儿");
   user2.setGroup(group);
   
   //不会抛出异常，因为采用了cascade属性，所以它会先保存Group
   //采用cascade属性是解决TransientObjectException异常的一种手段   
   session.save(user1);
   session.save(user2);
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   User user = (User)session.load(User.class, 3);
   System.out.println("user.name=" + user.getName());
   System.out.println("user.group.name=" + user.getGroup().getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

 

hibernate一对一主键关联映射（单向关联Person---->IdCard）

一对一主键关联映射:让两个实体对象的id保持相同，这样可以避免多余的字段被创建

具体映射：

 <id name="id">
  <!-- person的主键来源idCard，也就是共享idCard的主键 -->
  <generator class="foreign">
   <param name="property">idCard</param>
  </generator>
 </id>
 <property name="name"/>
 <!-- one-to-one标签的含义，指示hibernate怎么加载它的关联对象，默认根据主键加载，
 constrained="true"， 表明当前主键上存在一个约束，person的主键作为外键参照了idCard 
  -->
 <one-to-one name="idCard" constrained="true"/>

IdCard.hbm.xml

<?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>
 <class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="cardNo"/>
 </class>
</hibernate-mapping>

Person.hbm.xml

<?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>
 <class name="com.bjsxt.hibernate.Person" table="t_person">
  <id name="id">
   <generator class="foreign">
    <param name="property">idCard</param>
   </generator>
  </id>
  <property name="name"/>
  <one-to-one name="idCard" constrained="true"/>
 </class>
</hibernate-mapping>

 

public void testSave1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   IdCard idCard = new IdCard();
   idCard.setCardNo("88888888888888");
   
   Person person = new Person();
   person.setName("菜10");
   person.setIdCard(idCard);
   
   //不会出现TransientObjectException异常
   //因为一对一主键关联映射中，默认了cascade属性
   session.save(person);
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   User user = (User)session.load(User.class, 3);
   System.out.println("user.name=" + user.getName());
   System.out.println("user.group.name=" + user.getGroup().getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 

 

hibernate一对一主键关联映射（双向关联Person<---->IdCard）

 

IdCard.hbm.xml

<?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>
 <class name="com.bjsxt.hibernate.IdCard" table="t_idcard">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="cardNo"/>
  <one-to-one name="person"/>
 </class>
</hibernate-mapping>

 

 

public void testLoad2() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   IdCard idCard = (IdCard)session.load(IdCard.class, 1);
   System.out.println("idcard.cardNo=" + idCard.getCardNo());
   System.out.println("idcard.person.name=" + idCard.getPerson().getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

 

hibernate一对一唯一外键关联映射（单向关联Person---->IdCard）

 

一对一唯一外键关联映射是多对一关联映射的特例

可以采用<many-to-one>标签，指定多的一端的unique=true，这样就限制了多的一端的多重性为一
通过这种手段映射一对一唯一外键关联

 

Person.hbm.xml

<?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>
 <class name="com.bjsxt.hibernate.Person" table="t_person">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="name"/>
  <many-to-one name="idCard" unique="true"/>
 </class>
</hibernate-mapping>

 

public void testSave1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   IdCard idCard = new IdCard();
   idCard.setCardNo("88888888888888");
   
   Person person = new Person();
   person.setName("菜10");
   person.setIdCard(idCard);
   
   //不能成功保存，因为IdCard是Transient状态
   session.save(person);
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  
 
 public void testSave2() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   IdCard idCard = new IdCard();
   idCard.setCardNo("88888888888888");
   session.save(idCard);
   
   Person person = new Person();
   person.setName("菜10");
   person.setIdCard(idCard);
   // 成功
   session.save(person);
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }   
 public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   // 成功
   Person person = (Person)session.load(Person.class, 2);
   System.out.println("person.name=" + person.getName());
   System.out.println("idCard.cardNo=" + person.getIdCard().getCardNo());
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

hibernate一对一唯一外键关联映射（双向关联Person<---->IdCard）

 

一对一唯一外键关联双向，需要在另一端（idcard），添加<one-to-one>标签，指示hibernate如何加载
其关联对象，默认根据主键加载person，外键关联映射中，因为两个实体采用的是person的外键维护的关系，
所以不能指定主键加载person，而要根据person的外键加载，所以采用如下映射方式：
<one-to-one name="person" property-ref="idCard"/>