[SXT][WY]Hibernate09 Lazy策略

hibernate lazy策略可以使用在：
 * <class>标签上，可以取值：true/false
 * <property>标签上，可以取值：true/false需要类增强工具
 * <set><list>标签上，可以取值：true/false/extra
 * <one-to-one><many-to-one>单端关联上，可以取值：false/proxy/noproxy
 
lazy概念：只有真正使用该对象时，才会创建，对于hibernate而言，正真使用的时候才会发出sql

hibernate支持lazy策略只有在session打开状态下有效

<class>标签上的lazy特性只对普通属性起作用

 

Group.hbm.xml  class's default 'lazy' value is 'true'

 

<?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>

 

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Group group = (Group)session.load(Group.class, 1);
   
   //不会发出sql
   System.out.println("group.id=" + group.getId());
   
   //会发出sql
   System.out.println("group.name=" + group.getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }

 

public void testLoad2() {
  Session session = null;
  Group group = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   group = (Group)session.load(Group.class, 1);
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
  
  //不能正确输出，抛出LazyInitializationException 异常，因为session已经关闭
  //hibernate支持lazy策略只有在session打开状态下有效
  System.out.println("group.name=" + group.getName());
 } 

 

 

lazy_for_collection

hibernate在集合上的lazy策略，可以取值：true/false/extra

<class>标签上的lazy不会影响到集合上的lazy特性

 

// class lazy is default 'true'

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //会发出sql
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   
   //会发出sql
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Student student = (Student)iter.next();
    System.out.println("student.name=" + student.getName());
   }
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 

// class lazy is default 'true'

public void testLoad2() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //会发出sql
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   
   //会发出sql,发出查询全部数据的sql
   System.out.println("student.count=" + students.size());
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

// class lazy is 'false', but set lazy is default 'true'

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //不会发出sql
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   
   //会发出sql
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Student student = (Student)iter.next();
    System.out.println("student.name=" + student.getName());
   }
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }

 

/**
 * 设置集合上的lazy=false,其它默认
 */

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //会发出sql,会发出两条sql分别加载Classes和Student
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   
   //不会发出sql
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Student student = (Student)iter.next();
    System.out.println("student.name=" + student.getName());
   }
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 

/**
 * 设置集合上的lazy=false,其它默认
 */

public void testLoad2() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //会发出sql,会发出两条sql分别加载Classes和Student
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   
   //不会发出sql
   System.out.println("student.count=" + students.size());
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

/**
 * 设置集合上的lazy=extra,其它默认
 */

<?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="com.bjsxt.hibernate">
 <class name="Classes" table="t_classes">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="name"/>
  <set name="students" inverse="true" cascade="all" lazy="extra">
   <key column="classesid"/>
   <one-to-many class="Student"/>
  </set>
 </class>
</hibernate-mapping>

 

public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //会发出sql
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   
   //会发出sql
   for (Iterator iter=students.iterator(); iter.hasNext();) {
    Student student = (Student)iter.next();
    System.out.println("student.name=" + student.getName());
   }
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }

 

public void testLoad2() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   Classes classes = (Classes)session.load(Classes.class, 1);
   
   //会发出sql
   System.out.println("classes.name=" + classes.getName());
   
   //不会发出sql
   Set students = classes.getStudents();
   //会发出sql,发出一条比较智能的sql
   System.out.println("student.count=" + students.size());
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 }  

 

 

lazy_for_single_end

 

hibernate在单端关联上的lazy策略，可以取值：false/proxy/noproxy

<class>标签上的lazy不会影响到单端关联上的lazy特性

 

/**
 * 所有lazy属性默认
 */
public class SingleEndTest1 extends TestCase {
 
 public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   User user = (User)session.load(User.class, 1);
   
   //会发出sql
   System.out.println("user.name=" + user.getName());
   
   //不会发出sql
   Group group = user.getGroup();
   
   //会发出sql
   System.out.println("group.name=" + group.getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 
 
}

 

/**
 * 将<many-to-one>中的lazy设置为false,其它默认
 */
public class SingleEndTest2 extends TestCase {
 
 public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //不会发出sql
   User user = (User)session.load(User.class, 1);
   
   //会发出sql，发出两条sql分别加载User和Group
   System.out.println("user.name=" + user.getName());
   
   //不会发出sql
   Group group = user.getGroup();
   
   //不会发出sql
   System.out.println("group.name=" + group.getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 
 
}

 

/**
 * <class>标签上的lazy=false,其它默认
 */
public class SingleEndTest3 extends TestCase {
 
 public void testLoad1() {
  Session session = null;
  try {
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   //会发出sql
   User user = (User)session.load(User.class, 1);
   
   //不会发出sql
   System.out.println("user.name=" + user.getName());
   
   //不会发出sql
   Group group = user.getGroup();
   
   //会发出sql
   System.out.println("group.name=" + group.getName());
   
   session.getTransaction().commit();
  }catch(Exception e) {
   e.printStackTrace();
   session.getTransaction().rollback();
  }finally {
   HibernateUtils.closeSession(session);
  }
 } 
 
}