hibernate之主键生成策略

今天我们讲的hibernate的主键生成策略

hibernate的主键生成器:

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

主键生成的控制器

有很多种控制器：
1.assigned：程序员自己控制

1.2 数据库控制: identity(标识列/自动增长) sequence

1.3 hibernate控制:increment uuid/uuid.hex

1.4 其它:native

主键生成器的要求

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

步骤

下面我们来进行一个案例

首先我们根据上篇博客的基础上进行改造

第一步得加入一个辅助类，这个辅助类的作用就是用来检测所写的映射文件是否正确

    package com.yz.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框架之前应用）
 * 
 * 
 * 作用：
 * 可以用来检测所写的映射文件是否正确
 * @author 20190320
 *
 */
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();
	}
	
}

我们首先加入两个我们需要的xml文件，并且根据名字来建立两个实体类

首先是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.yz.two.entity.Student" table="tb_student">
		<id name="sid" type="java.lang.Integer" column="sid">
			<generator class="increment" />
<!-- 			<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>

接着是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.yz.two.entity.Worker" table="tb_worker">
		<id name="wid" type="java.lang.String" column="wid">
			<!--<generator class="uuid" />  -->
			<!-- <generator class="sequence" /> -->
			<!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
				</generator> -->
			 <generator class="com.yz.two.id.Myts" /> 
		</id>

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

实体类

实体类跟据xml文件中的设置的值来写
Student.java

package com.yz.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;
	}
	
}

Woker.java

package com.yz.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;
	}
	
}

接下来写完这些基础的东西，再写一个dao方法实现这些功能

dao方法

package com.dao;

import java.io.Serializable;

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

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

public class DemoDao {
	
	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 addWork(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.setSname("dabao");
		dao.addStudent(stu);
		System.out.println(dao.addStudent(stu));
	}
	
	public static void main(String[] args) {
		DemoDao dao = new DemoDao();
		Worker worker = new Worker();
		
		worker.setWname("dabao");
		dao.addWork(worker);
		System.out.println(dao.addWork(worker));
	}
}

再创一个id主键生成器

package com.yz.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 arg0, Object arg1) throws HibernateException {
		// TODO Auto-generated method stub
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return "yz_shop_book_"+sdf.format(new Date());
	}

}

最后的结果

然后数据库是
Student的数据库是

Woreker的数据库加入数据后