hibernate主键生成器

it2026-02-13 16

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。

案例： student实体类

package com.likang.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) { super(); this.sid = sid; this.sname = sname; } public Student() { super(); } }

worker实体类

package com.likang.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 + "]"; } public Worker(String wid, String wname) { super(); this.wid = wid; this.wname = wname; } public Worker() { super(); } }

student映射文件 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.likang.two.entity.Student" table="t_hibernate_student"> <id name="sid" type="java.lang.Integer" column="sid">  <generator class="identity" />     </id> <property name="sname" type="java.lang.String" column="sname"> </property> </class> </hibernate-mapping>

worker的映射文件 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.likang.two.entity.Worker" table="t_hibernate_worker"> <id name="wid" type="java.lang.String" column="wid"> <generator class="assigned" />     </id> <property name="wname" type="java.lang.String" column="wname"> </property> </class> </hibernate-mapping>

两个映射文件配置到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>  <property name="connection.username">root</property> <property name="connection.password">123</property> <property name="connection.url">jdbc:mysql://localhost:3306/mysql?useUnicode=true&characterEncoding=UTF-8 </property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</property>  <property name="hibernate.current_session_context_class">thread</property>  <property name="show_sql">true</property> <property name="format_sql">true</property>  <mapping resource="com/likang/one/entity/User.hbm.xml" />  <mapping resource="com/likang/two/entity/Student.hbm.xml" /> <mapping resource="com/likang/two/entity/Worker.hbm.xml" /> </session-factory> </hibernate-configuration>

工具包 SessionFactoryUtils 仅在学习hibernate的工程中使用，当进入spring的学习后就没用了，后面会有ssh来替代它作用：用来检测hibernate中的配置文件的准确性 hibernate.cfg.xml *.hbm.xml

package com.likang.two.util; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; /** * 仅在学习hibernate的工程中使用，当进入spring的学习后就没用了，后面会有ssh来替代它 * 作用： * 用来检测hibernate中的配置文件的准确性 * hibernate.cfg.xml * *.hbm.xml * @author Hasee * */ public class SessionFactoryUtils { private static SessionFactory sessionFactory; static { Configuration cfg = new Configuration().configure("/hibernate.cfg.xml"); sessionFactory = cfg.buildSessionFactory(); } public static Session openSession() { // 从本地的线程中获取session会话，第一次肯定是获取不到的，那么需要重新让session factor创建一个session会话 // 第二次就能够第一次创建的session反复利用，节约性能 Session session = sessionFactory.getCurrentSession(); if(session == null) { session = sessionFactory.openSession(); } return session; } 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()); } }

这个工具能够使你在运行时发现 hibernate.cfg.xml和 *.hbm.xml的错误 1.1 程序员自己控制：assigned 数据类型不限、保存前必须赋值

DomeDao

package com.likang.two.dao; import org.hibernate.Session; import org.hibernate.Transaction; import com.likang.two.entity.Student; import com.likang.two.entity.Worker; import com.likang.two.util.SessionFactoryUtils; /** * hibernate中的主键生成策略 * 1，人工控制 * 2，数据库控制 * 3，hibernate控制 * 4，自定义生成策略 * @author Hasee * */ 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(); Worker worker=new Worker(); worker.setWname("李康"); worker.setWid("10086"); dao.addWorker(worker); } }

1.2 数据库控制: identity(标识列/自动增长) sequence 数字，无需赋值先将表设置为标识列 dao

package com.likang.two.dao; import org.hibernate.Session; import org.hibernate.Transaction; import com.likang.two.entity.Student; import com.likang.two.entity.Worker; import com.likang.two.util.SessionFactoryUtils; /** * hibernate中的主键生成策略 * 1，人工控制 * 2，数据库控制 * 3，hibernate控制 * 4，自定义生成策略 * @author Hasee * */ 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(); Student stu=new Student(); stu.setSname("李康"); stu.setSid(78); dao.addStudent(stu); }

因为数据库卡死的问题，所有这里就不展示结果了；结果应该为是sid不为78,而是表中最大sid的自增长 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

3. 自定义主键生成器

3.1 *.hbm.xml指定主键生成器类

MyTsGenerator

package com.likang.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 MyTsGenerator 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 "book_order_"+sdf.format(new Date()); } }

dao

package com.likang.two.dao; import org.hibernate.Session; import org.hibernate.Transaction; import com.likang.two.entity.Student; import com.likang.two.entity.Worker; import com.likang.two.util.SessionFactoryUtils; /** * hibernate中的主键生成策略 * 1，人工控制 * 2，数据库控制 * 3，hibernate控制 * 4，自定义生成策略 * @author Hasee * */ 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 testStudent() { DemoDao dao=new DemoDao(); Student stu=new Student(); stu.setSname("李康"); stu.setSid(78); dao.addStudent(stu); } public static void main(String[] args) { DemoDao dao=new DemoDao(); Worker worker=new Worker(); worker.setWname("李康"); worker.setWid("10086"); dao.addWorker(worker); } } <generator class="com.likang.two.id.MyTsGenerator" />

最新回复(0)