Hibernate5-多对1(n:1)-fetch="select"-lazy="false"

1.创建项目,项目名称hibernatedemo27,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">
<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="false"/>
</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="false"
*/
@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();
}
}
}