hibernate主键生成策略

Posted 2022-06-03 xiatian3452

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 。

首先我们引入一个工具类SessionFactoryUtils

package com.liuwenwu.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框架之前用)
 * 作用：
 *       可以用来检测所写的映射文件是否正确  90%
 * @author ASUS
 *
 */
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() 
        //获取本地线程中的会话
        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();
    

这个类可以用来检测所写的映射文件是否出错  如果有错则如下图：

要实现hibernate的主键生成 我们先创两个实体类 

Student:

 

package com.liuwenwu.two.entity;

import java.io.Serializable;

public class Student implements Serializable

    /**
     * 
     */
    private static final long serialVersionUID = 374274097567290896L;
    
    private int sid;
    private String sname;
    public int getSid() 
        return sid;
    
    public void setSid(int 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:

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

然后对实体类进行配置：

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.liuwenwu.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" />  -->
            <!-- hibernate控制 -->
             <generator class="increment" />
             <!-- 数据库控制 -->
             <!-- <generator class="identity" /> -->
             <!-- 数据库控制 -->
            <!-- <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：

<?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.liuwenwu.two.entity.Worker" table="t_hibernate_worker">
        <id name="wid" type="java.lang.String" column="wid">
            <!-- 程序员自己控制 -->
            <!-- <generator class="assigned" /> -->
            <!-- 由容器自动生成的一个32位的字符串 -->
            <!-- <generator class="uuid" /> -->
            <!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
                </generator> -->
            <!-- 自定义主键生成器 -->
            <generator class="com.liuwenwu.two.id.Myts" />
        </id>

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

主配置文件 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/t224?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>
        <!-- <property name="dialect">org.hibernate.dialect.OracleDialect</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/liuwenwu/one/entity/User.hbm.xml" />
        <!--主键生成策略 -->
        <mapping resource="com/liuwenwu/two/entity/Student.hbm.xml" />
        <mapping resource="com/liuwenwu/two/entity/Worker.hbm.xml" />
    </session-factory>
</hibernate-configuration>

编写dao方法来进行测试

DemoDao:

package com.liuwenwu.two.dao;

import java.io.Serializable;

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

import com.liuwenwu.two.entity.Student;
import com.liuwenwu.two.entity.Worker;
import com.liuwenwu.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 save = session.save(stu);
        transaction.commit();
        session.close();
        return save;    
    
    
    /**
     * 添加工人
     * @param wor
     * @return
     */
    public Serializable addWorker(Worker wor) 
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Serializable save = session.save(wor);
        transaction.commit();
        session.close();
        return save;    
    
    
    public static void testStudent(String[] args) 
        DemoDao demoDao=new DemoDao();
        Student stu=new Student();
//        stu.setSid(8);
        stu.setSname("毛三");
        System.out.println(demoDao.addStudent(stu));;    
    
    
    public static void main(String[] args) 
        DemoDao demoDao=new DemoDao();
        Worker worker=new Worker();
        worker.setWname("毛三");
        System.out.println(demoDao.addWorker(worker));;    
    

几种不同的主键生成方式：

1.程序员自己控制：assigned     完全由程序员自己控制,不管数据库表怎么建,必须由程序员自己提供ID

 

 

2.数据库控制: identity (根据数据库设置的标识列来实现自定增长自动增长)

　　2.1sequence ：  使用hibernate中的默认序列 所有表共用一个序列 会出现跳号现象 不建议使用
　　　　　使用时可以指定序列 <param name="sequence_name">aaa</param>
　　　　　无缝跨平台：在主配置文件中修改数据库方言 可实现跨平台生成主键

 

 Mysql语句：

 

 Oracle语句：

 

 

3 .hibernate控制:increment  跟数据库没关系 ID必须是数字的

4 .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

 

 

5.自定义主键生成器：创建主键生成器类

 

实现org.hibernate.id.IdentifierGenerator接口即可,并还可以实现org.hibernate.id.Configurable接口来读取一些配置信息
自己定义主键规则   Myts:

package com.liuwenwu.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 "zking_shop_bood"+sdf.format(new Date());
    

效果：自己定义前缀+主键生成时间