学步园

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>
10        <property name="name"/>
11        <set name="students" inverse="true" cascade="all" lazy="extra">
12            <key column="classesid"/>
13            <one-to-many class="Student"/>
14        </set>
15    </class>
16</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>
10        <property name="name"/>
11        <many-to-one name="classes" column="classesid"/>
12    </class>
13</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;
10
11/** *//**
12 * 保持lazy默认
13 * @author Administrator
14 *
15 */
16public class CellectionlazyTest1 extends TestCase {
17
18
19    public void testLoad1() {
20        Session session = null;
21        try {
22            session = HibernateUtils.getSession();
23            session.beginTransaction();
24            
25            //不会发出sql
26            Classes classes = (Classes)session.load(Classes.class, 1);
27            
28            //会发出sql
29            System.out.println("classes.name=" + classes.getName());
30            
31            //不会发出sql
32            Set students = classes.getStudents();
33            
34            //会发出sql
35            for (Iterator iter=students.iterator(); iter.hasNext();) {
36                Student student = (Student)iter.next();
37                System.out.println("student.name=" + student.getName());
38            }
39            session.getTransaction().commit();
40        }catch(Exception e) {
41            e.printStackTrace();
42            session.getTransaction().rollback();
43        }finally {
44            HibernateUtils.closeSession(session);
45        }
46    }    
47    
48    public void testLoad2() {
49        Session session = null;
50        try {
51            session = HibernateUtils.getSession();
52            session.beginTransaction();
53            
54            //不会发出sql
55            Classes classes = (Classes)session.load(Classes.class, 1);
56            
57            //会发出sql
58            System.out.println("classes.name=" + classes.getName());
59            
60            //不会发出sql
61            Set students = classes.getStudents();
62            
63            //会发出sql,发出查询全部数据的sql
64            System.out.println("student.count=" + students.size());
65            session.getTransaction().commit();
66        }catch(Exception e) {
67            e.printStackTrace();
68            session.getTransaction().rollback();
69        }finally {
70            HibernateUtils.closeSession(session);
71        }
72    }        
73}
74

 

 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;
10
11/** *//**
12 * 设置<class>标签上的lazy=false
13 * @author Administrator
14 *
15 */
16public class CellectionlazyTest2 extends TestCase {
17
18
19    public void testLoad1() {
20        Session session = null;
21        try {
22            session = HibernateUtils.getSession();
23            session.beginTransaction();
24            
25            //会发出sql
26            Classes classes = (Classes)session.load(Classes.class, 1);
27            
28            //不会发出sql
29            System.out.println("classes.name=" + classes.getName());
30            
31            //不会发出sql
32            Set students = classes.getStudents();
33            
34            //会发出sql
35            for (Iterator iter=students.iterator(); iter.hasNext();) {
36                Student student = (Student)iter.next();
37                System.out.println("student.name=" + student.getName());
38            }
39            session.getTransaction().commit();
40        }catch(Exception e) {
41            e.printStackTrace();
42            session.getTransaction().rollback();
43        }finally {
44            HibernateUtils.closeSession(session);
45        }
46    }    
47}

 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;
10
11/** *//**
12 * 设置集合上的lazy=false,其它默认
13 * @author Administrator
14 *
15 */
16public class CellectionlazyTest3 extends TestCase {
17
18
19