hibernate之主键生成策略

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 。

我们先写实体类：

Student.java

package com.huang.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.java

package com.huang.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();
    }
    
    
}

工具类：

Sessionfactory.java 

package com.huang.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，进入spring的学习后会有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
 *             *.hbm.xml
 * @author Admin
 *
 */
 
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());
    }
}

程序员自己控制：assigned

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

 数据库控制: identity(标识列/自动增长) sequence

然后在hibernate.cfg.xml中添加实体映射文件（主键生成策略）

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">huang</property>
        <property name="connection.password">root</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/huang?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>

        <!-- 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/huang/one/entity/User.hbm.xml" />
        <!-- 主键生成策略 -->
        <mapping resource="com/huang/two/entity/Student.hbm.xml" />
        <mapping resource="com/huang/two/entity/Worker.hbm.xml" />
    </session-factory>
</hibernate-configuration>

然后测试一下

DemoDao.java

  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、自定义主键生成策略

package com.huang.two.dao;


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

import com.huang.two.entity.Student;
import com.huang.two.entity.Worker;
import com.huang.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();
　　　　　　　　Student stu=new Student();
　　　　　　　　stu.setSname("huang");
　　　　　　　　stu.setSid(110);
　　　　　　　　dao.addStudent(stu);
　　　　}

 } 

DemoDao.java

package com.huang.two.dao;


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

import com.huang.two.entity.Student;
import com.huang.two.entity.Worker;
import com.huang.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、自定义主键生成策略
 * @author Admin
 *
 */
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("huang");
            stu.setSid(110);
            dao.addStudent(stu);
        }
        
        public static void main(String[] args) {
            DemoDao dao=new DemoDao();
            Worker worker=new Worker();
            worker.setWname("旺财狗");
            dao.addWorker(worker);
        }
        
}