Hibernate之主键生成策略

最新推荐文章于 2020-08-30 18:07:11 发布

原创最新推荐文章于 2020-08-30 18:07:11 发布 · 128 阅读

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CC 4.0 BY-SA版权

本文探讨了ORM中实体类与数据库表映射的方法，包括程序员控制、数据库控制及框架控制的ID生成策略。通过具体示例展示了不同场景下ID生成的实现，如assigned、identity、increment以及自定义生成器的使用。

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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

entity（实体类）
Student
代码：

package com.pengyuxuan.two.entity;

public class Student {
	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 + "]";
	}
	public Student(Integer sid, String sname) {
		this.sid = sid;
		this.sname = sname;
	}
	public Student() {
	}

}

Worker
代码：

package com.pengyuxuan.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;
	}
	public Worker(String wid, String wname) {
		this.wid = wid;
		this.wname = wname;
	}
	public Worker() {
	}
	@Override
	public String toString() {
		return "Worker [wid=" + wid + ", wname=" + wname + "]";
	}

}

Student.hbm.xml
代码：

<?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.pengyuxuan.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>

Worker.hbm.xml
代码：

<?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.pengyuxuan.two.entity.Worker" table="t_hibernate_worker">
		<id name="wid" type="java.lang.String" column="wid">
			<!-- <generator class="assigned" />-->
			<generator class="com.pengyuxuan.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>

DemoDao
代码：

package com.pengyuxuan.two.dao;

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

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

public class DemoDao {
	
		/**
		 * 新增学生
		 * @param stu
		 */
		public void addStudent(Student stu) {
			Session session = SessionFactoryUtils.openSession();
			Transaction transaction = session.beginTransaction();
			session.save(stu);
			transaction.commit();
			SessionFactoryUtils.closeSession();
		}
		/**
		 * 新增工人
		 * @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 main(String[] args) {
			DemoDao dao=new DemoDao();
//			第一种   assigned 程序员自己控制
//			Student stu=new Student();
//			stu.setSname("风琴杨");
//			stu.setSid(72);
//			dao.addStudent(stu);
//			第二种 identity 数据库控制
//			Student stu2=new Student();
//			stu2.setSname("林肯");
//			stu2.setSid(79);
//			dao.addStudent(stu2);
//			第三种 increment hibernate控制
			Worker stu3=new Worker();
			Worker worker=new Worker();
			worker.setWname("德州");
			dao.addWorker(worker);	
		}
	}

运行效果
在这里插入图片描述

MyTsGenerator
代码：

package com.pengyuxuan.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;

import com.pengyuxuan.two.dao.DemoDao;
import com.pengyuxuan.two.entity.Worker;

public class MyTsGenerator implements IdentifierGenerator {

	@Override

		public Serializable generate (SharedSessionContractImplementor session, Object object) throws HibernateException {
			// TODO Auto-generated method stub
			SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			return "book_order_"+sdf.format(new Date());
		}
	public static void main(String[] args) {
		DemoDao dao=new DemoDao();

		Worker worker=new Worker();
		worker.setWname("德州");
		dao.addWorker(worker);
	}

	}

把Worker.hbm.xml的配置文件改为

	<generator class="com.pengyuxuan.two.ID.MyTsGenerator" />

效果：
在这里插入图片描述