hibernate之主键生成策略

1. hibernate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 。

主键生成器要求

1 assigned数据类型不限、保存前必须赋值

2 identity(重点掌握)数字，无需赋值

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

4 increment 数字，无需赋值

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，

6 native(重点掌握)等于identity+sequence

hibernate.cfg.xml

<?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>
		<!-- 1. 数据库相关 -->
		<property name="connection.username">root</property>
		<property name="connection.password">123</property>
		<property name="connection.url">jdbc:mysql://localhost:3306/mybatis_ssm?useUnicode=true&amp;characterEncoding=UTF-8
		</property>
		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

		<!-- 配置本地事务（No CurrentSessionContext configured!） -->
		<property name="hibernate.current_session_context_class">thread</property>

		<!-- 2. 调试相关 -->
		<property name="show_sql">true</property>
		<property name="format_sql">true</property>

		<!-- 3. 添加实体映射文件 -->
		<mapping resource="com/huangwen/one/entity/User.hbm.xml" />
		<!-- 主建生成器-->
		<mapping resource="com/huangwen/two/entity/Student.hbm.xml"/>
		<mapping resource="com/huangwen/two/entity/Worker.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

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.huangwen.two.entity.Student" table="t_hibernate_student">
		<id name="sid" type="java.lang.Integer" column="sid">
			<generator class="assigned" />
<!-- 			<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>

Student

package com.huangwen.two.entity;

public class Student {
	
	private Integer sid;
	private String sname;
	public Student(Integer sid, String sname) {
		super();
		this.sid = sid;
		this.sname = sname;
	}
	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + 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;
	}
	
	public Student() {
		// TODO Auto-generated constructor stub
	}

}

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.huangwen.two.entity.Worker" table="t_hibernate_worker">
		<id name="wid" type="java.lang.String" column="wid">
			<!-- <generator class="assigned" />-->
			<generator class="com.huangwen.two.id.MyTsGenerator" />
			<!-- <generator class="sequence" /> -->
			<!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
				</generator> -->
			<!-- <generator class="com.javaxl.two.id.Myts" /> -->
		</id>

		<property name="wname" type="java.lang.String" column="wname">
		</property>
	</class>
</hibernate-mapping>

Worker

package com.huangwen.two.entity;

public class Worker {
	
	private String wid;
	private String wname;
	
	public Worker() {
		// TODO Auto-generated constructor stub
	}

	public Worker(String wid, String wname) {
		super();
		this.wid = wid;
		this.wname = 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 + "]";
	}	
}

SessionFactoryUtils

package com.huangwen.two.util;

import org.hibernate.Session;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

/**
 * 仅在学习hibernate的工程中使用，当进入spring的学习后就没用了，后面会有ssh来替代
 * 作用：
 *     用来检测hibernate中配置文件的准确性
 *       hibernate.cfg.xml
 *       *.hbm.xml
 *       
 * @author Administrator
 *
 */
public class SessionFactoryUtils {
	private static SessionFactory sessionFactory;
	static {
		Configuration cfg = new Configuration().configure("hibernate.cfg.xml");
		sessionFactory = cfg.buildSessionFactory();
	}
	
	public static Session openSession() {
//		从本地的线程中获取session回话，第一次肯定是获取不到的，那么需要重新让sessionfactory创建一个session出来
//		第二次就能够对第一次创建的session反复利用，节约性能
		Session session = sessionFactory.getCurrentSession();
		if(session == null) {
			session = sessionFactory.openSession();
		}
		return session;
	}
	
	public static void closeSession() {
		Session session = sessionFactory.getCurrentSession();
		if(session != null && session.isOpen()) {
			session.close();
		}
	}
	
	public static void main(String[] args) {
		Session session = SessionFactoryUtils.openSession();
		session.beginTransaction();
		System.out.println(session.isConnected());
		SessionFactoryUtils.closeSession();
		System.out.println(session.isConnected());
	}
}

MyTsGenerator

package com.huangwen.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 MyTsGenerator implements IdentifierGenerator {


	@Override
	public Serializable generate(SharedSessionContractImplementor arg0, Object arg1) throws HibernateException {
		SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return "book_order_"+sdf.format(new Date());
	}

}

DemoDao

package com.huangwen.two.dao;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.huangwen.two.entity.Student;
import com.huangwen.two.entity.Worker;
import com.huangwen.two.util.SessionFactoryUtils;

/**
 * hibernate中的主建生成策略
 * 1.人工控制
 * 2.数据库控制
 * 3.hibernate控制
 * 4.自定义主建生成策略
 * 
 * @author dell
 *
 */
public class DemoDao {
	
	/**
	 * 增加学生
	 * @param stu
	 */
	public void addStudent(Student stu){
		Session session=SessionFactoryUtils.openSession();
		Transaction transaction=session.beginTransaction();
		session.save(stu);
		transaction.commit();
		SessionFactoryUtils.closeSession();
	}
	
	/**
	 * 增加工人
	 * @param worker
	 */
	public void addWorker(Worker worker){
		Session session=SessionFactoryUtils.openSession();
		Transaction transaction=session.beginTransaction();
		session.save(worker);
		transaction.commit();
		SessionFactoryUtils.closeSession();
	}
	
	public static void testStudent() {
		DemoDao dao=new DemoDao();
		Student stu=new Student();
		stu.setSname("111");
		stu.setSid(70);
		dao.addStudent(stu);
	}
	
	
	public static void main(String[] args) {
		DemoDao dao=new DemoDao();
		Worker worker=new Worker();
		worker.setWname("小小黑hhh");
		dao.addWorker(worker);
	
	}
}