（二）Hibernate之主键生成策略

大大源码 • 2023年3月12日 am12:27 • 其他

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。

1.1 程序员自己控制： assigned

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

公司名_模块名_时间戳

2. 主键生成器要求
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

代码演示：
Entity包:
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.qiuwenfan.two.entity.Student" table="t_hibernate_student">
		<id name="sid" type="java.lang.Integer" column="sid">
			<!-- <generator class="assigned" /> -->    <!-- 程序员自己控制 -->
			<!-- <generator class="identity" /> -->             <!-- 数据库控制(标识列/自动增长) -->
			<!-- <generator class="increment" /> -->   <!-- hibernate控制 -->
			<generator class="sequence" />
			<!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
				</generator> -->
			<!-- <generator class="com.qiuwenfan.two.id.Myts" /> -->
		</id>
		<property name="sname" type="java.lang.String" column="sname">
		</property>
	</class>
</hibernate-mapping>

Student.java:（学生）

package com.azuo.two.entity;

public class Student {
	private Integer sid;
	private String sname;
	
	public Student() {
		super();
	}

	public Student(Integer sid, String sname) {
		super();
		this.sid = sid;
		this.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;
	}

	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + "]";
	}
	
}

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.qiuwenfan.two.entity.Worker" table="t_hibernate_worker">
		<id name="wid" type="java.lang.String" column="wid">
			<!-- <generator class="uuid" />   -->           <!-- 随机生成 -->
			<!-- <generator class="assigned" /> -->
			<!-- <generator class="sequence" /> -->
			<!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
				</generator> -->
			<generator class="com.qiuwenfan.two.id.Myts" />
		</id>

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

Worker.java:

package com.azuo.two.entity;

public class Worker {
	 private String wid;
	 private String wname;
	 
	public Worker() {
		super();
	}

	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 + "]";
	}
}

Util包：
SessionFactoryUtils.Java:

package com.azuo.two.util;

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

/**
 * 本工具类的作用
 * 1、简化代码的书写
 * 2、检测hibernate相关的配置是否正确
 * 
 * @author zuo_fan
 *
 */
public class SessionFactoryUtils {
	private static SessionFactory sessionFactory;
	static {
		Configuration cfg = new Configuration().configure("/hibernate.cfg.xml");
		sessionFactory = cfg.buildSessionFactory();
	}
	
	//开启
	public static Session openSession() {
		Session session = sessionFactory.getCurrentSession();
		if(session == null) {
			session = sessionFactory.openSession();
		}
		return session;
	}
	
	//关闭
	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());
	}
}

Dao包：
DemoDao.java：

package com.azuo.two.dao;

import java.io.Serializable;

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

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

public class DemoDao {
	/**
	 * 添加学生
	 * @param stu
	 * @return
	 */
	public Serializable addStu(Student stu) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();//开启事务
		
		Serializable save = session.save(stu);//返回事务
		
		transaction.commit();
		SessionFactoryUtils.closeSession();
		
		return save;
	}
	
	/**
	 * 添加打工仔
	 * @param stu
	 * @return
	 */
	public Serializable addWorker(Worker worker) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();//开启事务
		
		Serializable save = session.save(worker);
		
		transaction.commit();
		SessionFactoryUtils.closeSession();
		
		return save;
	}
}

DemoDaoTest.java:

package com.azuo.two.dao;

import static org.junit.Assert.*;

import java.io.Serializable;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.azuo.two.entity.Student;
import com.azuo.two.entity.Worker;

public class DemoDaoTest {
	private DemoDao demoDao = new DemoDao();
	
	@Before
	public void setUp() throws Exception {
//		System.out.println("测试所有要测试的方法之前都会执行的内容（一般用来初始化数据所用）");
	}
	
	@After
	public void tearDown() throws Exception {
//		System.out.println("测试所有要测试的方法之后都会执行的内容（一般用来释放资源所用）");
	}

	@Test
	public void testAddStu() {
		Student stu = new Student();
		stu.setSname("基佬4");
		stu.setSid(86);
		demoDao.addStu(stu);
	}

	@Test
	public void testAddWorker() {
		Worker worker = new Worker();
		worker.setWid("w41bb");
		worker.setWname("拜拜！！！！");
		Serializable wid = demoDao.addWorker(worker);
		System.out.println(wid);
	}

}

Myts.java:

package com.azuo.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 "book_category_"+sdf.format(new Date());
	}

}

在这里插入图片描述

原文链接：https://blog.csdn.net/zuo_fan/article/details/103942871

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