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Hibernate5-多对一双向关联-fetch="select",lazy="proxy"
1.创建项目,项目名称hibernatedemo29,目录结构如图所示
2.在项目中创建lib目录存储jar文件,目录结构如图所示
3.在src目录中创建实体类Forum,包名(com.mycompany.demo.bean),如图所示
4.实体类Forum的内容如下
package com.mycompany.demo.bean;
import java.util.Set;
public class Forum {
private int fid;
private String name;
private Set<ForumPost> forumPosts;
public int getFid() {
return fid;
}
public void setFid(int fid) {
this.fid = fid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<ForumPost> getForumPosts() {
return forumPosts;
}
public void setForumPosts(Set<ForumPost> forumPosts) {
this.forumPosts = forumPosts;
}
}5.在src目录中创建实体类Forum的映射文件Forum.hbm.xml,包名(com.mycompany.demo.bean),如图所示
6.映射文件Forum.hbm.xml的内容如下
<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- package:指定<class/>所在的包 --> <hibernate-mapping package="com.mycompany.demo.bean"> <!-- name:类名 table:表名 catalog:数据库名称,默认为hibernate.cfg.xml中配置的数据库名称 --> <class name="Forum" table="forum" lazy="true"> <meta attribute="class-description"> This class contains the forum detail. </meta> <!-- name:属性名 colum:列名 --> <id name="fid" type="int" column="fid"> <!-- increment:hibernate维护主键值 identity:数据库自增长 sequence:序列 native:根据不同的数据库选择生成策略 uuid:通过UUID算法生成,实际使用较多 assigned:手工设置 --> <generator class="native"/> </id> <!-- length:字节长度 type:字段类型,支持java和hibernate类型 not-null:非空约束 unique:唯一性约束 --> <property name="name" column="name" /> <!-- lazy: false:直接加载 true:延迟加载 extra:特别延迟加载 fetch join:迫切左外连接 select:普通select查询 subselect :子查询方式 --> <set name="forumPosts"> <key column="fid"/> <one-to-many class="ForumPost"/> </set> </class> </hibernate-mapping>
7.在src目录中创建实体类ForumPost,包名(com.mycompany.demo.bean),如图所示
8.实体类ForumPost的内容如下
package com.mycompany.demo.bean;
public class ForumPost {
private int pid;
private String subject;
private Forum forum;
public int getPid() {
return pid;
}
public void setPid(int pid) {
this.pid = pid;
}
public String getSubject() {
return subject;
}
public void setSubject(String subject) {
this.subject = subject;
}
public Forum getForum() {
return forum;
}
public void setForum(Forum forum) {
this.forum = forum;
}
}9.在src目录中创建实体类ForumPost的映射文件ForumPost.hbm.xml,包名(com.mycompany.demo.bean),如图所示
10.映射文件ForumPost.hbm.xml的内容如下
<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- package:指定<class/>所在的包 --> <hibernate-mapping package="com.mycompany.demo.bean"> <!-- name:类名 table:表名 catalog:数据库名称,默认为hibernate.cfg.xml中配置的数据库名称 --> <class name="ForumPost" table="forumpost"> <meta attribute="class-description"> This class contains the forumpost detail. </meta> <!-- name:属性名 colum:列名 --> <id name="pid" type="int" column="pid"> <!-- increment:hibernate维护主键值 identity:数据库自增长 sequence:序列 native:根据不同的数据库选择生成策略 uuid:通过UUID算法生成,实际使用较多 assigned:手工设置 --> <generator class="native"/> </id> <!-- length:字节长度 type:字段类型,支持java和hibernate类型 not-null:非空约束 unique:唯一性约束 --> <property name="subject" column="subject" type="string" length="50" not-null="true" unique="false"/> <!-- name:关联属性 column:关联属性在数据库对应的字段 class:关联属性所对应的类型 --> <many-to-one name="forum" class="Forum" column="fid" cascade="save-update" fetch="select" lazy="proxy"/> </class> <query name="queryAll">from Forum f left outer join fetch f.forumPosts</query> </hibernate-mapping>
11.在src目录中创建工具类 HbnUtil,包名(com.mycompany.demo.util),如图所示
12.工具类 HbnUtil的内容如下
package com.mycompany.demo.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HbnUtil {
private static SessionFactory sessionFactory;
public static Session getSession(){
if(sessionFactory == null || sessionFactory.isClosed()){
sessionFactory = new Configuration().configure().buildSessionFactory();
}
return sessionFactory.getCurrentSession();
}
}13.在src目录中创建Hibernate的配置文件hibernate.cfg.xml,如图所示
14.Hibernate的配置文件hibernate.cfg.xml的内容如下
<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration SYSTEM "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <!-- 方言,可以从Hibernate核心jar(hibernate-core-x.x.x.Finall.jar) 文件中的or.hibernate.dialect包中找到相应的类,类的全名就是 --> <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property> <!-- 驱动 --> <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> <!-- 数据库连接地址 --> <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property> <!-- 用户名 --> <property name="hibernate.connection.username"> root </property> <!-- 密码 --> <property name="hibernate.connection.password"></property> <!-- create:每次都新创建,如果存在就删除 create-drop:创建新表,sessionFactory关闭,表会删除 update :表字段增加,会同步,字段减少不同步,数据改变会同步修改 --> <property name="hibernate.hbm2ddl.auto">update</property> <!-- 输出sql --> <property name="hibernate.show_sql">true</property> <!-- 格式化sql --> <property name="hibernate.format_sql">true</property> <!-- 事务环境一个线程对一个事务 thread:本地事务环境 jta:分布式事务环境 SpringSessionContext:用于ssh整合 --> <property name="hibernate.current_session_context_class">thread</property> <!-- 使用c3p0数据源 --> <property name="hibernate.connection.provider_class"> org.hibernate.c3p0.internal.C3P0ConnectionProvider</property> <!-- List of XML mapping files --> <mapping resource="com/mycompany/demo/bean/Forum.hbm.xml"/> <mapping resource="com/mycompany/demo/bean/ForumPost.hbm.xml"/> </session-factory> </hibernate-configuration>
15.在项目中创建test目录存储测试文件,文件名称TestApp,包名(com.mycompany.demo.bean),目录结构如图所示
16.TestApp测试类的内容如下
package com.mycompany.demo.bean;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.sql.JoinType;
import org.junit.Before;
import org.junit.Test;
import com.mycompany.demo.util.HbnUtil;
public class TestApp {
private Session session;
@Before
public void init(){
session = HbnUtil.getSession();
}
/*
* 一对多双向关联-添加
* 需要设置Forum.hbm.xml中的Set属性为cascade="all"
*/
@Test
public void testOneToManyAdd(){
try {
session.beginTransaction();
ForumPost forumPost1 = new ForumPost();
forumPost1.setSubject("A");
ForumPost forumPost2 = new ForumPost();
forumPost2.setSubject("B");
Set<ForumPost> forumPosts = new HashSet<ForumPost>();
forumPosts.add(forumPost1);
forumPosts.add(forumPost2);
Forum forum = new Forum();
forum.setName("foruma");
forum.setForumPosts(forumPosts);
session.save(forum);
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
}
}
/*
* 多对一双向关联-fetch="select",lazy="proxy",在一的一方的class标签中添加lazy="true"属性
*/
@Test
public void testFetchForSelect(){
try {
session.beginTransaction();
ForumPost forumPost = session.get(ForumPost.class, 10);
Forum forum = forumPost.getForum();
System.out.println(forum.getFid());
System.out.println(forum.getName());
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
}
}
}
本文出自 “素颜” 博客，谢绝转载！
Hibernate5-多对一双向关联-fetch="select",lazy="proxy"
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