hibernate主键生成策略

Posted 2022-06-29 hyfl

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

 1 package com.liuwenwu.two.util;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.cfg.Configuration;
 6 /**
 7  * 这个类是在学习hibernate 的过程中所用(整合SSH框架之前用)
 8  * 作用：
 9  *       可以用来检测所写的映射文件是否正确  90%
10  * @author ASUS
11  *
12  */
13 public class SessionFactoryUtils 
14     private static SessionFactory sessionFactory;
15 //    存放当前会话
16     private static ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
17     static 
18         Configuration cfg = new Configuration();
19         Configuration configure = cfg.configure("/hibernate.cfg.xml");
20         sessionFactory = configure.buildSessionFactory();
21     
22     
23     public static Session openSession() 
24         //获取本地线程中的会话
25         Session session = threadLocal.get();
26         if (null == session) 
27             session = sessionFactory.openSession();
28             threadLocal.set(session);
29         
30         return session;
31     
32 
33     public static void closeSession() 
34         Session session = threadLocal.get();
35         if (null != session) 
36             if (session.isOpen()) 
37                 session.close();
38             
39             threadLocal.set(null);
40         
41     
42 
43     public static void main(String[] args) 
44         Session session = openSession();
45         System.out.println(session.isConnected());
46         closeSession();
47     
48 

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:

 1 package com.liuwenwu.two.entity;
 2 
 3 import java.io.Serializable;
 4 
 5 public class Student implements Serializable
 6 
 7     /**
 8      * 
 9      */
10     private static final long serialVersionUID = 374274097567290896L;
11     
12     private int sid;
13     private String sname;
14     public int getSid() 
15         return sid;
16     
17     public void setSid(int sid) 
18         this.sid = sid;
19     
20     public String getSname() 
21         return sname;
22     
23     public void setSname(String sname) 
24         this.sname = sname;
25     
26     @Override
27     public String toString() 
28         return "Student [sid=" + sid + ", sname=" + sname + "]";
29     
30 

Worker:

 1 package com.liuwenwu.two.entity;
 2 
 3 public class Worker 
 4     private String wid;
 5     private String wname;
 6     public String getWid() 
 7         return wid;
 8     
 9     public void setWid(String wid) 
10         this.wid = wid;
11     
12     public String getWname() 
13         return wname;
14     
15     public void setWname(String wname) 
16         this.wname = wname;
17     
18     @Override
19     public String toString() 
20         return "Worker [wid=" + wid + ", wname=" + wname + "]";
21     
22 

然后对实体类进行配置：

Student.hbm.xml：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 <hibernate-mapping>
 6     <class name="com.liuwenwu.two.entity.Student" table="t_hibernate_student">
 7         <id name="sid" type="java.lang.Integer" column="sid">
 8             <!-- 程序员自己控制 -->
 9             <!-- <generator class="assigned" />  -->
10             <!-- hibernate控制 -->
11              <generator class="increment" />
12              <!-- 数据库控制 -->
13              <!-- <generator class="identity" /> -->
14              <!-- 数据库控制 -->
15             <!-- <generator class="sequence" /> -->
16             <!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
17                 </generator> -->
18             <!-- <generator class="com.javaxl.two.id.Myts" /> -->
19         </id>
20         <property name="sname" type="java.lang.String" column="sname">
21         </property>
22     </class>
23 </hibernate-mapping>

Worker.hbm.xml：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 <hibernate-mapping>
 6     <class name="com.liuwenwu.two.entity.Worker" table="t_hibernate_worker">
 7         <id name="wid" type="java.lang.String" column="wid">
 8             <!-- 程序员自己控制 -->
 9             <!-- <generator class="assigned" /> -->
10             <!-- 由容器自动生成的一个32位的字符串 -->
11             <!-- <generator class="uuid" /> -->
12             <!-- <generator class="sequence" > <param name="sequence_name">aaa</param> 
13                 </generator> -->
14             <!-- 自定义主键生成器 -->
15             <generator class="com.liuwenwu.two.id.Myts" />
16         </id>
17 
18         <property name="wname" type="java.lang.String" column="wname">
19         </property>
20     </class>
21 </hibernate-mapping>

主配置文件 hibernate.cfg.xml：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3     "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 5     
 6     <hibernate-configuration>
 7     <session-factory>
 8         <!-- 1. 数据库相关 -->
 9         <property name="connection.username">root</property>
10         <property name="connection.password">123</property>
11         <property name="connection.url">jdbc:mysql://localhost:3306/t224?useUnicode=true&amp;characterEncoding=UTF-8
12         </property>
13         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
14         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
15         <!-- <property name="dialect">org.hibernate.dialect.OracleDialect</property> -->
16         
17         <!-- 配置本地事务（No CurrentSessionContext configured!） -->
18         <property name="hibernate.current_session_context_class">thread</property>
19 
20         <!-- 2. 调试相关 -->
21         <property name="show_sql">true</property>
22         <property name="format_sql">true</property>
23 
24         <!-- 3. 添加实体映射文件 -->
25         <mapping resource="com/liuwenwu/one/entity/User.hbm.xml" />
26         <!--主键生成策略 -->
27         <mapping resource="com/liuwenwu/two/entity/Student.hbm.xml" />
28         <mapping resource="com/liuwenwu/two/entity/Worker.hbm.xml" />
29     </session-factory>
30 </hibernate-configuration>

编写dao方法来进行测试

DemoDao:

 1 package com.liuwenwu.two.dao;
 2 
 3 import java.io.Serializable;
 4 
 5 import org.hibernate.Session;
 6 import org.hibernate.Transaction;
 7 
 8 import com.liuwenwu.two.entity.Student;
 9 import com.liuwenwu.two.entity.Worker;
10 import com.liuwenwu.two.util.SessionFactoryUtils;
11 
12 public class DemoDao 
13 
14     /**
15      * 添加学生
16      * @param stu
17      * @return
18      */
19     public Serializable addStudent(Student stu) 
20         Session session = SessionFactoryUtils.openSession();
21         Transaction transaction = session.beginTransaction();
22         Serializable save = session.save(stu);
23         transaction.commit();
24         session.close();
25         return save;    
26     
27     
28     /**
29      * 添加工人
30      * @param wor
31      * @return
32      */
33     public Serializable addWorker(Worker wor) 
34         Session session = SessionFactoryUtils.openSession();
35         Transaction transaction = session.beginTransaction();
36         Serializable save = session.save(wor);
37         transaction.commit();
38         session.close();
39         return save;    
40     
41     
42     public static void testStudent(String[] args) 
43         DemoDao demoDao=new DemoDao();
44         Student stu=new Student();
45 //        stu.setSid(8);
46         stu.setSname("毛三");
47         System.out.println(demoDao.addStudent(stu));;    
48     
49     
50     public static void main(String[] args) 
51         DemoDao demoDao=new DemoDao();
52         Worker worker=new Worker();
53         worker.setWname("毛三");
54         System.out.println(demoDao.addWorker(worker));;    
55     
56 

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:

 1 package com.liuwenwu.two.id;
 2 
 3 import java.io.Serializable;
 4 import java.text.SimpleDateFormat;
 5 import java.util.Date;
 6 
 7 import org.hibernate.HibernateException;
 8 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 9 import org.hibernate.id.IdentifierGenerator;
10 
11 public class Myts implements IdentifierGenerator
12 
13     @Override
14     public Serializable generate(SharedSessionContractImplementor session, Object object) throws HibernateException 
15         SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
16         return "zking_shop_bood"+sdf.format(new Date());
17     
18 

效果：自己定义前缀+主键生成时间