Hibernate之主键生成策略
今天分享是hibernate映射框架的主键自动生成器
一：Hibernate主键生成器
generator元素：表示了一个主键生成器，它用来为持久化类实例生成唯一的标识 。
1.1 程序员自己控制：assigned （不管数据库中列段如何设置，最终控制权在程序员手中，他想干嘛就得干嘛）
1.2 数据库控制: identity(标识列/自动增长) sequence（在hibernate内置的序列号默认的情况下所有关于hibernate的表都会使用，从而出现跳号的现象，不建议使用）
1.3 hibernate控制:increment uuid/uuid.hex
1.4 其它:native
二：主建生成器的要求
2.1 assigned
数据类型不限、保存前必须赋值
2.2 identity(重点掌握)
数字，无需赋值
2.3 sequence(重点掌握)
数字，无需赋值， 默认使hibernate_sequence这个序列，
也可以通过sequence/sequence_name参数赋值
2.4 increment
数字，无需赋值
2.5 uuid/uuid.hex (是由容器自动生成的一个32位的字符串，.hex代表的是十六进制)
32位的字符串，无需赋值，
2.6 native(重点掌握)
等于identity+sequence
三：展示案例
首先设计两个表
学生表 t_hibernate_student
工人表 t_hibernate_worker
创建工具类SessionFactoryUtils，用来检测所写映射文件是否正确
package com.ht.two.util; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; /** * 这个类是在学习hibernate的过程中所用（整合SSH框架之前用） * @author Administrator */ public class SessionFactoryUtils { private static SessionFactory sessionFactory; // 存放当前会话 private static ThreadLocal<Session> threadLocal = new ThreadLocal<Session>(); static { Configuration cfg = new Configuration(); Configuration configure = cfg.configure("/hibernate.cfg.xml"); sessionFactory = configure.buildSessionFactory(); } public static Session openSession() { Session session = threadLocal.get(); if (null == session) { session = sessionFactory.openSession(); threadLocal.set(session); } return session; } public static void closeSession() { Session session = threadLocal.get(); if (null != session) { if (session.isOpen()) { session.close(); } threadLocal.set(null); } } public static void main(String[] args) { Session session = openSession(); System.out.println(session.isConnected()); closeSession(); } }
创建与表对应的实体类
Student类
package com.ht.two.entity; import java.io.Serializable; public class Student implements Serializable{ private Integer sid; private String sname; public Integer getSid() { return sid; } public void setSid(Integer sid) { this.sid = sid; } public String getSname() { return sname; } public void setSname(String sname) { this.sname = sname; } }
worker类
package com.ht.two.entity; public class Worker { private String wid; private String wname; public String getWid() { return wid; } public void setWid(String wid) { this.wid = wid; } public String getWname() { return wname; } public void setWname(String wname) { this.wname = wname; } @Override public String toString() { return "Worker [wid=" + wid + ", wname=" + wname + "]"; } }
在创建对应的映射文件
Student.hbm.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.ht.two.entity.Student" table="t_hibernate_student"> <id name="sid" type="java.lang.Integer" column="sid"> <!-- <generator class="assigned" /> --> <generator class="identity" /><!--自增、标识列--> <!-- <generator class="increment" /> --> <!-- <generator class="sequence" /> --> <!-- <generator class="sequence" > <param name="sequence_name">aaa</param> </generator> --> <!-- <generator class="com.javaxl.two.id.Myts" /> --> </id> <property name="sname" type="java.lang.String" column="sname"> </property> </class> </hibernate-mapping>
Worker.hbm.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.ht.two.entity.Worker" table="t_hibernate_worker"> <id name="wid" type="java.lang.String" column="wid"> <!-- <generator class="assigned" /> --> <!-- <generator class="sequence" /> --> <!-- <generator class="sequence" > <param name="sequence_name">aaa</param> </generator> --> <generator class="com.ht.two.id.Myst" /> </id> <property name="wname" type="java.lang.String" column="wname"> </property> </class> </hibernate-mapping>
测试类
package com.ht.two.Dao; import java.io.Serializable; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import com.ht.two.entity.Student; import com.ht.two.entity.Worker; import com.ht.two.util.SessionFactoryUtils; public class DemoDao { /** * 添加学生 * @param student * @return */ public Serializable addStudent(Student student) { Session session=SessionFactoryUtils.openSession(); Transaction transaction=session.beginTransaction(); Serializable saveId=session.save(student); transaction.commit(); session.close(); return saveId; } /** * 添加工人 * @param worker * @return */ public Serializable addWorker(Worker worker) { Session session=SessionFactoryUtils.openSession(); Transaction transaction=session.beginTransaction(); Serializable saveId=session.save(worker); transaction.commit(); session.close(); return saveId; } /** * 学生测试 * @param args */ public static void main(String[] args) { DemoDao dao=new DemoDao(); Student student=new Student(); // student.setSid(5); student.setSname("青灯"); System.out.println(dao.addStudent(student)); } /** * 工人测试 * @param args */ // public static void main(String[] args) { // DemoDao dao=new DemoDao(); // Worker worker=new Worker(); // worker.setWid("1"); // worker.setWname("hhhh"); // System.out.println(dao.addWorker(worker)); // } }
自定义主建生成器
实现org.hibernate.id.IdentifierGenerator接口即可,并还可以实现org.hibernate.id.Configurable接口来读取一些配置信息
PersistentIdentifierGenerator.TABLE
PersistentIdentifierGenerator.PK
package com.ht.two.id; import java.io.Serializable; import java.text.SimpleDateFormat; import java.util.Date; import org.hibernate.HibernateException; import org.hibernate.engine.spi.SharedSessionContractImplementor; import org.hibernate.id.IdentifierGenerator; public class Myst implements IdentifierGenerator{ @Override public Serializable generate(SharedSessionContractImplementor arg0, Object arg1) throws HibernateException { // TODO Auto-generated method stub SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); return "daqing_youtian_ht_"+format.format(new Date()); } }
今日分享到此结束！！！谢谢观看！！！
