(3)Hibernate3.2 中的 one-to-one关系

Hibernate 是一个很强大的ORM 框架。

仅仅在 one-to-one中就分 单向关联,使用连接表的单向关联,双向关联,使用连接表的双向关联.

这里以 双向关联为主总结一下。

 

1 关联文件的书写.
com.isw2.entity.UserBO.java 如下:

public class UserBO extends BaseBO {
	private Long userId;
	private String userName;
	private UserInfoBO userInfoBO;

UserBO.hbm.xml如下;

<class name="com.isw2.entity.UserBO" table="t_user" lazy="true">
		<id name="userId" column="userId">
			<generator class="native"></generator>
		</id>
		<property name="userName" column="userName" length="30"
			type="string">
		</property>
		<!--  多对一中设置 unique = true
			<many-to-one name="userInfoBO" cascade="all" column="infoId" unique="true" lazy="proxy"></many-to-one>
		-->
               <!-- cascade="all" 使用级联更新,fetch="select" 使用单独的语句查询相关联对象 -->
		<one-to-one name="userInfoBO" class="com.isw2.entity.UserInfoBO"
			cascade="all" fetch="select">
		</one-to-one>
</class>

 

 com.isw2.entity.UserInfoBO.java 如下:

public class UserBO extends BaseBO {
	private Long userId;
	private String userName;
	private UserInfoBO userInfoBO;

 UserInfoBO.hbm.xml:

<class name="com.isw2.entity.UserInfoBO" table="t_user_info"
	lazy="true">
	<id name="userId" column="userId">
		<generator class="foreign">
			<param name="property">UserBO</param>
		</generator>
	</id>
	<property name="userSex" column="userSex" length="2"
		type="string">
	</property>
	<!-- constrained="true" 添加外键约束 -->
	<one-to-one name="userBO" constrained="true"
		class="com.isw2.entity.UserBO" fetch="select" cascade="all">
	</one-to-one>
</class>

 2 相关查询.

/**
 * 存储对象
 * 
 * @param userBO
 *            要save的对象
 */
public void save(UserBO userBO) {
	Session session = HibernateSessionFactory.getSession();
	Transaction tr = session.beginTransaction();
	session.save(userBO);
	tr.commit();
	session.close();
}

/**
 * 查找所有对象
 */
public void findAll() {
	Session session = HibernateSessionFactory.getSession();
	Transaction tr = session.beginTransaction();
	Query query = session.createQuery("from UserBO");
	List list = query.list();
	for (Object object : list) {
		System.out.println(object);
	}
	tr.commit();
	session.close();
}

/**
 * 使用HQL语句查询
 */
public void findByHQL() {
	// 连接查询
	String hqlString = "select new UserBO(ub.userId,ub.userName,ib) from UserBO ub,UserInfoBO ib where ub.userId = ib.userId";
	Session session = HibernateSessionFactory.getSession();
	Transaction tr = session.beginTransaction();
	Query query = session.createQuery(hqlString);
	List list = query.list();
	for (Object object : list) {
		System.out.println(object);
	}
	tr.commit();
	session.close();
}

/**
 * 使用Criteria 查询
 */
public void findByCriteria() {
	// DetachedCriteria dc = DetachedCriteria.forClass(UserBO.class);
	// DetachedCriteria 是Criteria的离线版
	Session session = HibernateSessionFactory.getSession();
	Criteria cr = session.createCriteria(UserBO.class);
	cr.addOrder(Order.asc("userName"));
	// cr.setProjection(Projections.max("userId")); 使用聚集函数

	// cr.add(Restrictions.gt("userId", new Long(3)));使用Restrictions

	// Criteria crUserInfo = cr.createCriteria("userInfoBO");
	// crUserInfo.add(Restrictions.eq("userSex", "男"));使用多表联接查询

	List list = cr.list();
	for (Object object : list) {
		System.out.println(object);
	}
	session.close();
}

/**
 * Example查询
 */
public void findByExample() {
	Session session = HibernateSessionFactory.getSession();
	UserInfoBO userInfo = new UserInfoBO();
	userInfo.setUserSex("男");
	Example emample = Example.create(userInfo);
	Criteria cr = session.createCriteria(UserInfoBO.class);
	cr.add(emample);
	List list = cr.list();
	for (Object object : list) {
		UserInfoBO info = (UserInfoBO) object;
		System.out.println(info.getUserBO().toString());
	}
	session.close();
}

/**
 * Cascade = all 级联更新
 */
public void deleteCascade() {
	Session session = HibernateSessionFactory.getSession();
	UserBO userBO = (UserBO) session.load(UserBO.class, new Long(3));
	Transaction tr = session.beginTransaction();
	session.delete(userBO);
	tr.commit();
	session.close();

 3 one-to-one 中关延迟加载.

在当前例子中为又向关联，UserBO主表 , UserInfoBO 从表.
首先 one-to-one 中 fetch="select" 是必须的它表示默认不使用连接查询.

但是因为one-to-one 的特殊性，查询UserBO 过程中无法使用延迟加载，UserInfoBO 中则可以使用.(参考http://ch-space.iteye.com/blog/390780)