hibernate之主键生成策略
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 。
连接数据库的xml
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/sys?useUnicode=true&characterEncoding=UTF-8 </property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</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/jt/entity/User.hbm.xml"/> <!--主键生成策略 --> <mapping resource="com/jt2/entity/Student.hbm.xml"/> <mapping resource="com/jt2/entity/Worker.hbm.xml"/> </session-factory> </hibernate-configuration>
Student.java
package com.jt2.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; } public Student(Integer sid, String sname) { super(); this.sid = sid; this.sname = sname; } public Student() { super(); // TODO Auto-generated constructor stub } @Override public String toString() { return "Student [sid=" + sid + ", sname=" + sname + "]"; } }
Worker.java
package com.jt2.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) { super(); this.wid = wid; this.wname = wname; } public Worker() { super(); // TODO Auto-generated constructor stub } @Override public String toString() { return "Worker [wid=" + wid + ", wname=" + wname + "]"; } }
实体类映射文件
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.jt2.entity.Student" table="t_hibernate_student"> <id name="sid" type="java.lang.Integer" column="sid"> <!-- <generator class="assigned" /> --> <!-- <generator class="identity" /> --> <generator class="increment" /> <!-- <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
<?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.jt2.entity.Worker" table="t_hibernate_worker"> <id name="wid" type="java.lang.String" column="wid"> <!-- <generator class="assigned" /> --> <!-- <generator class="sequence" /> --> <!-- <generator class="uuid" /> --> <generator class="com.jt2.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>
还有个工具类
SessionFactoryUtils.java
package com.jt2.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来代替它 * * 作用： * 用来检测hibernate中的配置文件的准确性 * hibernate.cfg.xml * *.hbn.xml * @author jt * */ 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sessionfactory创建一个session出来 //第二次就能够对第一次创建的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()); } }
做测试用dao层做我们建一个
DemoDao.java
package com.jt2.dao; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import com.jt2.entity.Student; import com.jt2.entity.Worker; import com.jt2.util.SessionFactoryUtils; /** * hibernate中的主键生成策略 * 1，人工控制 * 2，数据库控制 * 3，hibrenate控制 * 4，自定义主键生成策略 * @author jt * */ 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(); } /** * 新增功能 * @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(String[] args) { DemoDao dao=new DemoDao(); Student stu=new Student(); stu.setSname("哈哈哈"); stu.setSid(71); dao.addStudent(stu); } public static void main(String[] args) { DemoDao dao=new DemoDao(); Worker worker=new Worker(); worker.setWname("jt"); dao.addWorker(worker); } }
最后建一个
MyTsGenerator.java
package com.jt2.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 session, Object object) throws HibernateException { SimpleDateFormat sdf=new SimpleDateFormat("yyyy-mm-dd HH:mm:ss"); return "book_order_"+sdf.format(new Date()); } }
然后我们把DemoDao.java里面的的测试数据改下
这就是成功了，今天就到这里了
