hibernate在集合上的lazy策略

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

例子：

 1<?xml version="1.0"?>
 2<!DOCTYPE hibernate-mapping PUBLIC 
 3    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 5<hibernate-mapping package="com.bjsxt.hibernate">
 6    <class name="Classes" table="t_classes">
 7        <id name="id">
 8            <generator class="native"/>
 9        </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>

 

 1<?xml version="1.0"?>
 2<!DOCTYPE hibernate-mapping PUBLIC 
 3    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 5<hibernate-mapping>
 6    <class name="com.bjsxt.hibernate.Student" table="t_student">
 7        <id name="id">
 8            <generator class="native"/>
 9        </id>
        <property name="name"/>
        <many-to-one name="classes" column="classesid"/>
    </class>
</hibernate-mapping>

 

 1package com.bjsxt.hibernate;
 2
 3import java.util.HashSet;
 4import java.util.Iterator;
 5import java.util.Set;
 6
 7import junit.framework.TestCase;
 8
 9import 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);
        }
    }        
}

 

 1package com.bjsxt.hibernate;
 2
 3import java.util.HashSet;
 4import java.util.Iterator;
 5import java.util.Set;
 6
 7import junit.framework.TestCase;
 8
 9import org.hibernate.Session;

/** *//**
 * 设置<class>标签上的lazy=false
 * @author Administrator
 *
 */
public class CellectionlazyTest2 extends TestCase {


    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);
        }
    }    
}

 1package com.bjsxt.hibernate;
 2
 3import java.util.HashSet;
 4import java.util.Iterator;
 5import java.util.Set;
 6
 7import junit.framework.TestCase;
 8
 9import 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);
        }
    }        
}

 1package com.bjsxt.hibernate;
 2
 3import java.util.HashSet;
 4import java.util.Iterator;
 5import java.util.Set;
 6
 7import junit.framework.TestCase;
 8
 9import 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);
        }
    }        
}