类级别的检索策略

来源：互联网发布：网络语言pc是什么意思编辑：程序博客网时间：2024/06/08 13:15

持久化类：

Clazz.java

package com.baidu.clazzStrategy;import java.util.HashSet;import java.util.Set;//站在Clazz 的角度   单向    1 对  多  。 1 这一端public class Clazz {/** * orders *  * 1. 声明集合类型时，需要使用接口类型， * 因为hibernate 在获取集合类型时，返回的是Hibernate 内置的集合类型， * 而不是JaveSE 的一个标准的集合实现 * 2. 需要把集合进行初始化，可防止 发生空指针异常 */private Integer clazzId;private String  clazzName;private Set<Student> stus = new HashSet<Student>();下面是getter 和 setter}

Student.java

package com.baidu.clazzStrategy;// 单向    1 对  多  。 多这一端public class Student {private Integer stuId;private String stuName;下面getter 和 setter}

对象关系映射

Clazz.hbm.xml

<hibernate-mapping package="com.baidu.clazzStrategy"><!-- lazy 类级别的懒加载 -->    <class name="Clazz" table="CLAZZS" lazy="true">            <id name="clazzId" type="java.lang.Integer">            <column name="CLAZZ_ID" />            <generator class="native" />        </id>                <property name="clazzName" type="java.lang.String">            <column name="CLAZZ_NAME" />        </property>                <set name="stus" table="STUDENTS" inverse="false">            <key>                <column name="CLAZZ_ID" />            </key>            <one-to-many class="Student" />        </set>            </class>    </hibernate-mapping>

Student.hbm.xml

<hibernate-mapping package="com.baidu.clazzStrategy">    <class name="Student" table="STUDENTS">            <id name="stuId" type="java.lang.Integer">            <column name="STU_ID" />            <generator class="native" />        </id>                <property name="stuName" type="java.lang.String">            <column name="STU_NAME" />        </property>            </class>    </hibernate-mapping>

测试：

package com.baidu.clazzStrategy;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.hibernate.service.ServiceRegistryBuilder;import org.junit.After;import org.junit.Before;import org.junit.Test;public class Test12N {private  SessionFactory sessionFactory;private  Session session;private  Transaction transaction;@Beforepublic void init(){Configuration configuration = new Configuration().configure();ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()).buildServiceRegistry();sessionFactory = configuration.buildSessionFactory(serviceRegistry);session = sessionFactory.openSession();transaction = session.beginTransaction();System.out.println("init....");}@Afterpublic void destroy(){transaction.commit();session.close();sessionFactory.close();System.out.println("destory....");}/** * lazy 当类上的lazy 属性设置为fasle 时， 表示为立即加载 * lazy 当类上的lazy 属性设置为true 时， 表示为延迟加载 */@Testpublic void testGet() {Clazz clazz = (Clazz) session.load(Clazz.class, 1);System.out.println(clazz.getClass());System.out.println(clazz.getClazzId());System.out.println(clazz.getStus().size());}}

lazy 当类上的lazy 属性设置为fasle 时，表示为立即加载

Hibernate:     select        clazz0_.CLAZZ_ID as CLAZZ_ID1_0_0_,        clazz0_.CLAZZ_NAME as CLAZZ_NA2_0_0_     from        CLAZZS clazz0_     where        clazz0_.CLAZZ_ID=?class com.baidu.clazzStrategy.Clazz1Hibernate:     select        stus0_.CLAZZ_ID as CLAZZ_ID3_0_1_,        stus0_.STU_ID as STU_ID1_1_1_,        stus0_.STU_ID as STU_ID1_1_0_,        stus0_.STU_NAME as STU_NAME2_1_0_     from        STUDENTS stus0_     where        stus0_.CLAZZ_ID=?2

lazy 当类上的lazy 属性设置为true 时，表示为延迟加载

class com.baidu.clazzStrategy.Clazz_$$_javassist_11Hibernate:     select        clazz0_.CLAZZ_ID as CLAZZ_ID1_0_0_,        clazz0_.CLAZZ_NAME as CLAZZ_NA2_0_0_     from        CLAZZS clazz0_     where        clazz0_.CLAZZ_ID=?Hibernate:     select        stus0_.CLAZZ_ID as CLAZZ_ID3_0_1_,        stus0_.STU_ID as STU_ID1_1_1_,        stus0_.STU_ID as STU_ID1_1_0_,        stus0_.STU_NAME as STU_NAME2_1_0_     from        STUDENTS stus0_     where        stus0_.CLAZZ_ID=?2

0 0