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 。

1.1 程序员自己控制：assigned
1.2 数据库控制: identity(标识列/自动增长) sequence
1.3 hibernate控制:increment uuid/uuid.hex
1.4 其它:native

2. 主键生成器要求

2.1 assigned
数据类型不限、保存前必须赋值

2.2 identity
数字，无需赋值

2.3 sequence
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
等于identity+sequence

案例

package com.two.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

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() {
		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();
	}
	
}

写两个实体类:

package com.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 + "]";
	}
	
}

package com.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 + "]";
	}
	
}

实体类的配置xml:
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.two.entity.Worker" table="t_hibernate_worker">
		<id name="wid" type="java.lang.String" column="wid">
			<generator class="assigned" />
			<!-- <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>

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.two.entity.Student" table="t_hibernate_student">
		<id name="sid" type="java.lang.Integer" column="sid">
			<generator class="assigned" />
<!-- 			<generator class="increment" /> -->
			 <!-- <generator class="identity" /> --> 
			<!-- <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>

然后在hibernate.cfg.xml配置主键生成策略

<?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/db_school?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.MySQL5InnoDBDialect</property>
		<property name="hbm2ddl.auto">update</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/one/entity/User.hbm.xml" />
		<!-- 4.主键生成策略 -->
		<mapping resource="com/two/entity/Student.hbm.xml" />
		<mapping resource="com/two/entity/Worker.hbm.xml" />
	</session-factory> 
</hibernate-configuration>

Demo

package com.two.dao;

import java.io.Serializable;

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

import com.two.entity.Student;
import com.two.entity.Worker;
import com.two.util.SessionFactoryUtils;

public class DemoDao {
	/**
	 * 增加学生
	 * @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;
		
	}
	/**
	 * 增加工作者
	 * @param stu
	 * @return
	 */
	public Serializable addWorker(Worker w) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Serializable save = session.save(w);
		transaction.commit();
		session.close();
		return save;
		
	}

	
}

在Student.hbm.xml中 < generator class=“assigned” />:

	public static void main(String[] args) {
		DemoDao dao = new DemoDao();
		Student stu =  new Student();
		stu.setSid(1);
		stu.setSname("狗东西");
		System.out.println(dao.addStudent(stu ));
		
		
	}

效果:

增加成功:

在Student.hbm.xml中 < generator class=“sequence” />:

public static void main(String[] args) {
		DemoDao dao = new DemoDao();
		Student stu =  new Student();
		stu.setSname("狗子");
		System.out.println(dao.addStudent(stu));
		
	}

效果:

< generator class=“identity” /> 交给数据库维护:

在Worker.hbm.xml中 < generator class=“uuid” />:

	public static void main(String[] args) {
		DemoDao dao = new DemoDao();
		Worker w =  new Worker();
		w.setWname("狗兒子");
		System.out.println(dao.addWorker(w));
	}
	

成功:

3. 自定义主键生成器

*3.1 .hbm.xml指定主键生成器类

3.2 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
PersistentIdentifierGenerator.TABLE
PersistentIdentifierGenerator.PK
assigned、native、自定义主键

package com.two.dao;

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 arg0, Object arg1) throws HibernateException {
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return "zh_shopping_"+sdf.format(new Date());
	}
	
}

在Worker.hbm.xml中 < generator class=“com.two.dao.Myts” /> :