Hibernate之主键生成策略
ibernate的主键生成器:
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 意味不管你表是怎么建的你都得按照程序员的规矩来；不管你的表是不是自增列
1.2 数据库控制:1. identity(标识列/自动增长)
sequence（在mysql编程不建议使用，因为在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）
2. 指定用哪个序列：
<generator class="sequence" > <param name="序列表">xxx</param> </generator>
3.跨平台
1.3 hibernate控制:increment identity(标识列/自动增长)如果把数据库的自增列去掉就会报错，然而increment可以（它会去找你这个表里面的最大id）
uuid/uuid.hex
是指在一台机器上生成的数字，它保证对在同一时空中的所有机器都是唯一的
xxxxxxxx-xxxx-xxxx-xxxxxx-xxxxxxxxxx (8-4-4-4-12)
其中每个 x 是 0-9 或 a-f 范围内的一个十六进制的数字。
SessionFactoryUtils工具类：可以来检测所写的映射文件是否正确
package com.chenjiahao.two.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
/**
* 这个类是在学习hibernate的过程中所有（整合ssh框架之前用）
*
* 作用：
* 可以用来检测所写的映射文件是否正确
* @author dell
*
*/
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();
}
}
配置文件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.chenjiahao.two.entity.Worker" table="t_hibernate_worker">
<id name="wid" type="java.lang.String" column="wid">
<!-- <generator class="assigned" /> -->
<!-- <generator class="uuid" /> -->
<!-- 指定用哪个序列 -->
<!-- <generator class="sequence" > <param name="sequence_name">aaa</param>
</generator> -->
<!-- 自定义id -->
<generator class="com.chenjiahao.two.id.Myts" />
</id>
<property name="wname" type="java.lang.String" column="wname">
</property>
</class>
</hibernate-mapping>
配置文件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.chenjiahao.two.entity.Student" table="t_hibernate_student">
<id name="sid" type="java.lang.Integer" column="sid">
<!-- 程序员自己控制 -->
<!-- <generator class="assigned" /> -->
<!-- 数据库控制 -->
<generator class="increment" />
<!-- hibernate控制 -->
<!-- <generator class="identity" /> -->
<!-- 指定用哪个序列 -->
<!-- <generator class="sequence" > <param name="sequence_name">aaa</param>
</generator> -->
<!-- 自定义id -->
<!-- <generator class="com.javaxl.two.id.Myts" /> -->
</id>
<property name="sname" type="java.lang.String" column="sname">
</property>
</class>
</hibernate-mapping>
Student实体类：
package com.chenjiahao.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;
}
@Override
public String toString() {
return "Student [sid=" + sid + ", sname=" + sname + "]";
}
}
Worker实体类
package com.chenjiahao.two.entity;
import java.io.Serializable;
public class Worker implements Serializable{
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 + "]";
}
}
数据库表：
测试类：
package com.chenjiahao.two.dao;
import java.io.Serializable;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.chenjiahao.two.entity.Student;
import com.chenjiahao.two.entity.Worker;
import com.chenjiahao.two.util.SessionFactoryUtils;
public class DemoDao {
/**
* 添加学生
* @param stu
* @return
*/
public Serializable addStudent(Student stu) {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
Serializable saveId = session.save(stu);
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;
}
public static void testStudent(String[] args) {
DemoDao dao=new DemoDao();
Student stu=new Student();
// stu.setSid(1);
stu.setSname("旺财");
System.out.println(dao.addStudent(stu));
}
public static void main(String[] args) {
DemoDao dao=new DemoDao();
Worker worker=new Worker();
worker.setWname("钢弹");
System.out.println(dao.addWorker(worker));
}
}
自定义主键生成器：
package com.chenjiahao.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 Myts implements IdentifierGenerator{
@Override
public Serializable generate(SharedSessionContractImplementor session, Object object) throws HibernateException {
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH-mm-ss");
return "shop_book_"+sdf.format(new Date());
}
}
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