hibernate学习8之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


集合上的lazy策略

import org.hibernate.Session;

import junit.framework.TestCase;

/**
 * 运行本单元测试的条件：
 *  
 * 设置<class>标签上的lazy=true，也就是默认配置
 *  
 * @author Administrator
 *
 */
public class ClassLazyTest extends TestCase {

  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
//在Spring中设置openSessionInViewFilter可以解决这个问题。
    System.out.println("group.name=" + group.getName());
  } 
  
}

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

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import junit.framework.TestCase;

import org.hibernate.Session;

/**
 * 保持lazy默认
 * @author Administrator
 *
 */
public class CellectionlazyTest1 extends TestCase {


  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);
    }
  }   
}

设置集合上的lazy=false,其它默认

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import junit.framework.TestCase;

import org.hibernate.Session;

/**
 * 设置集合上的lazy=false,其它默认
 * @author Administrator
 *
 */
public class CellectionlazyTest3 extends TestCase {


  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);
    }
  } 
  
  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（推荐）,其它默认

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import junit.framework.TestCase;

import org.hibernate.Session;

/**
 * 设置集合上的lazy=extra,其它默认
 * @author Administrator
 *
 */
public class CellectionlazyTest4 extends TestCase {

  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);
    }
  }   
}

单端关联上的lazy策略

import org.hibernate.Session;

import junit.framework.TestCase;

/**
 * 所有lazy属性默认
 * @author Administrator
 *
 */
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);
    }
  } 
  
}

import org.hibernate.Session;

import junit.framework.TestCase;

/**
 * 将<many-to-one>中的lazy设置为false,其它默认
 * @author Administrator
 *
 */
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);
    }
  } 
  
}

import org.hibernate.Session;

import junit.framework.TestCase;

/**
 * <class>标签上的lazy=false,其它默认
 * @author Administrator
 *
 */
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);
    }
  } 
  
}