HibernateTools实现pojo类 数据库schma mapping映射的相互转换
核心
利用HibernateTools,用POJO类,Mapping映射文件,数据库表有其中的一项,就能生成其他两项。
概述
在使用Hibernate开发系统持久层时,按照一般开发流程,首先会从业务分析中获得业务实体,从而获得系统中真正需要的实体类,然后写Hibernate的mapping映射文件,最后根据映射文件,生成数据库表,以上这三步是Hibernate开发的起始。
根据开发习惯的不同,有些项目组可能会先写POJO类,有的项目可能会先设计数据库,有的项目组可能先写映射文件,其实完成其中的一项时,类结构或者表结构就可以确定了。
既然已经能确定结构了,完全可以使用工具来代替手工完成剩余的工作。
前提
安装Eclipse插件HibernateTools,eclipse插件安装百度下教程非常多,建议采用copy安装或者link安装,再有就是HibernateTools的版本对应着特定的Eclipse版本,所以安装前请先检查自己的eclipse版本。
然后建立项目,本文建立的是Dynamic Web Project,采用了mysql数据库,建立项目后,引入mysql的驱动jar,引入Hibernate(本文用了4.3.5版本)的包,即lib下required文件夹中所有jar
安装完了插件,首先利用tool生成Hibernate配置文件,项目右键-->new,安装完HibernateTools后,多了4种类型的文件,选择第一种:
根据使用的数据库,填入必须的属性:
生成hibernate.cfg.xml的代码:
<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <property name="hibernate.bytecode.use_reflection_optimizer">false</property> <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> <property name="hibernate.connection.password">123456</property> <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property> <property name="hibernate.connection.username">root</property> <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property> <property name="hibernate.search.autoregister_listeners">false</property> </session-factory> </hibernate-configuration></span>
相互转换
接下可以进入正题了,本文分别从三项中的每一项入手,生成其他两项。
思路一:由POJO类生成mapping映射文件和DDL
POJO类的代码写起来非常方便,因此首先介绍这种方法,个人认为这种方法效率最高。首先建立两个POJO类
package org.hibernate.test; public class Student implements java.io.Serializable { private int id; private String name; public Student() { } public Student(int id) { this.id = id; } public Student(int id, String name) { this.id = id; this.name = name; } public int getId() { return this.id; } public void setId(int id) { this.id = id; } public String getName() { return this.name; } public void setName(String name) { this.name = name; } }
package org.hibernate.test; import java.util.ArrayList; import java.util.List; public class Class implements java.io.Serializable { private int id; private String name; private List students = new ArrayList(0); public Class() { } public Class(int id) { this.id = id; } public Class(int id, String name, List students) { this.id = id; this.name = name; this.students = students; } public int getId() { return this.id; } public void setId(int id) { this.id = id; } public String getName() { return this.name; } public void setName(String name) { this.name = name; } public List getStudents() { return this.students; } public void setStudents(List students) { this.students = students; } }
接下来一步一步生成另外两项,首先项目右键-->new,选择Hibernate下面的第四项,建立mapping映射文件,根据已存在的POJO类,生成Mapping文件
下一步,可以预先查看生成的hbm.xml文件,有特殊要求的可以再生成的文件基础上稍作修改。
生成代码:
<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- Generated 2014-5-30 21:29:20 by Hibernate Tools 4.0.0 --> <hibernate-mapping> <class name="org.hibernate.test.Student" table="STUDENT"> <id name="id" type="int"> <column name="ID" /> <generator class="assigned"></generator> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> </class> </hibernate-mapping></span>
<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!-- Generated 2014-5-30 21:29:20 by Hibernate Tools 4.0.0 --> <hibernate-mapping> <class name="org.hibernate.test.Class" table="CLASS"> <id name="id" type="int"> <column name="ID" /> <generator class="assigned"></generator> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> <list name="students" inverse="false" table="STUDENT" lazy="true"> <key> <column name="ID" /> </key> <list-index> <column name="idx" /> </list-index> <one-to-many class="org.hibernate.test.Student" /> </list> </class> </hibernate-mapping></span>
mapping映射文件生成了,接下来生成ddl,项目右键-->new,选择Hibernate Console Configuration
选择好对应的项后,finish,然后需要在工具栏添加Hibernate code Generation,Windows-->Customer Perspective
然后工具栏多了一个很像运行按钮的图标,单击下拉按钮,选第二项
单击Exporters选项卡,可以看到HibernateTools工具能导出和生成的项很多,可以根据配置有针对性的选择自己想要的项,这里我们勾选Schema Export,然后单击图标1下面的Properties的Add,后出现图标2所示的窗体
选择第二项,这就是要生成我们想要的ddl,如图,当然上图还勾选了DAO Code,生成了操作试题的DAO代码(HibernateTools确实很贴心)
这是生成后的图片
ddl的建表语句:
<span style="font-family:KaiTi_GB2312;font-size:18px;">create table CLASS (ID integer not null, NAME varchar(255), primary key (ID)); create table STUDENT (ID integer not null, NAME varchar(255), idx integer, primary key (ID)); alter table STUDENT add index FKBACA0E1BE081A5FD (ID), add constraint FKBACA0E1BE081A5FD foreign key (ID) references CLASS (ID); </span>
DAO代码如下:
<span style="font-family:KaiTi_GB2312;font-size:18px;">package org.hibernate.test; // Generated 2014-5-30 23:18:05 by Hibernate Tools 4.0.0 import java.util.List; import javax.naming.InitialContext; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.hibernate.LockMode; import org.hibernate.SessionFactory; import org.hibernate.criterion.Example; /** * Home object for domain model class Class. * @see org.hibernate.test.Class * @author Hibernate Tools */ public class ClassHome { private static final Log log = LogFactory.getLog(ClassHome.class); private final SessionFactory sessionFactory = getSessionFactory(); protected SessionFactory getSessionFactory() { try { return (SessionFactory) new InitialContext() .lookup("SessionFactory"); } catch (Exception e) { log.error("Could not locate SessionFactory in JNDI", e); throw new IllegalStateException( "Could not locate SessionFactory in JNDI"); } } public void persist(Class transientInstance) { log.debug("persisting Class instance"); try { sessionFactory.getCurrentSession().persist(transientInstance); log.debug("persist successful"); } catch (RuntimeException re) { log.error("persist failed", re); throw re; } } public void attachDirty(Class instance) { log.debug("attaching dirty Class instance"); try { sessionFactory.getCurrentSession().saveOrUpdate(instance); log.debug("attach successful"); } catch (RuntimeException re) { log.error("attach failed", re); throw re; } } public void attachClean(Class instance) { log.debug("attaching clean Class instance"); try { sessionFactory.getCurrentSession().lock(instance, LockMode.NONE); log.debug("attach successful"); } catch (RuntimeException re) { log.error("attach failed", re); throw re; } } public void delete(Class persistentInstance) { log.debug("deleting Class instance"); try { sessionFactory.getCurrentSession().delete(persistentInstance); log.debug("delete successful"); } catch (RuntimeException re) { log.error("delete failed", re); throw re; } } public Class merge(Class detachedInstance) { log.debug("merging Class instance"); try { Class result = (Class) sessionFactory.getCurrentSession().merge( detachedInstance); log.debug("merge successful"); return result; } catch (RuntimeException re) { log.error("merge failed", re); throw re; } } public Class findById(int id) { log.debug("getting Class instance with id: " + id); try { Class instance = (Class) sessionFactory.getCurrentSession().get( "org.hibernate.test.Class", id); if (instance == null) { log.debug("get successful, no instance found"); } else { log.debug("get successful, instance found"); } return instance; } catch (RuntimeException re) { log.error("get failed", re); throw re; } } public List findByExample(Class instance) { log.debug("finding Class instance by example"); try { List results = sessionFactory.getCurrentSession() .createCriteria("org.hibernate.test.Class") .add(Example.create(instance)).list(); log.debug("find by example successful, result size: " + results.size()); return results; } catch (RuntimeException re) { log.error("find by example failed", re); throw re; } } }</span>
到此,我们就由POJO类,生成了hbm.xml文件和DDL
思路二:由hbm.xml生成POJO类和DDL
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思路三:由数据库表(或DDL)生成POJO类和hbm.xml
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思路二三请见下一博客!
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