Hibernate之主键生成策略

Hibernate之主键生成策略

Hibernate要求实体类里面有一个属性作为唯一值，对应表主键。

主键生成策略

主键生成器要求

generator	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 。
assigned	数据类型不限、保存前必须赋值
identity	数字，无需赋值 (重点掌握)
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
increment	数字，无需赋值
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，
native	等于identity+sequence

自定义主键生成器
*.hbm.xml指定主键生成器类

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

利用我们不同的主键所产生不同的策略：
首先看我们的 三个xml配置文件：
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.xzy.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">sequence_name</param> </generator> 
			<!-- <generator class="com.xzy.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.xzy.two.entity.Worker" table="t_hibernate_woker">
		<id name="wid" type="java.lang.String" column="wid">
<!-- 			<generator class="uuid" /> -->
<!-- 			<generator class="com.xzy.two.id.Myts" /> -->
		</id>

		<property name="wname" type="java.lang.String" column="wname">
		</property>
	</class>
</hibernate-mapping>

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/tb_ttt?useUnicode=true&amp;characterEncoding=UTF-8
		</property>
		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<!-- 		MySQL语音 -->
		<property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
<!-- 		Oracle语音 -->
<!-- 		<property name="dialect">org.hibernate.dialect.OracleDialect</property> -->

		<!-- 自动生成sequence_name序列表 -->
		<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/xzy/one/entity/User.hbm.xml"/>
		<!-- 讲解主键生成策略 -->
		<mapping resource="com/xzy/two/entity/Student.hbm.xml"/>
		<mapping resource="com/xzy/two/entity/Worker.hbm.xml"/>
		
	</session-factory>
</hibernate-configuration>

再看我们的DemoDao：

package com.xzy.two.dao;

import java.io.Serializable;

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

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

public class DemoDao implements Serializable{
	
	/**
	 * 添加学生
	 * @param stu
	 * @return
	 */
	public Serializable addStudent(Student stu) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Serializable saveId = session.save(stu);
		transaction.commit();
		session.close();
		return saveId;
	}
	
	public static void main(String[] args) {
		DemoDao dao = new DemoDao();
		Student stu = new Student();
		//stu.setSid(1);
		stu.setSname("Rookie、");
		System.out.println(dao.addStudent(stu));
	}
	}

添加下面这行代码写进hibernate.cfg.xml里会自动生成sequence_name序列表

<!-- 自动生成sequence_name序列表 -->
<!--自动序列化-->
		<property name="hbm2ddl.auto">update</property>

在Student.hbm.xml配置中打开这个自定义主键策略：

 <generator class="sequence" > <param name="sequence_name">sequence_name</param> </generator> 

然后运行，sequence_name这个序列表就自动生成到你的数据库里了

例子:利用uuid生成主键添加数据

实体类：Worker

package com.xzy.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;
	}
	
	public Worker(String wid, String wname) {
		super();
		this.wid = wid;
		this.wname = wname;
	}
	public Worker() {
		super();
	}	
}

DemoDao:

	/**
	 * 添加工人
	 * @param woker
	 * @return
	 */
	public Serializable addWoker(Worker worker) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Serializable saveId = session.save(worker);
		transaction.commit();
		session.close();
		return saveId;
	}

	public static void main(String[] args) {
		DemoDao dao = new DemoDao();
		Worker worker = new Worker();
//		worker.setWid("");
		worker.setWname("环卫工人");
		System.out.println(dao.addWoker(worker));
	}
	

最后我们写一个自定义主键生成器：

Myts.java:需实现org.hibernate.id.IdentifierGenerator接口即可

package com.xzy.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 Myts implements IdentifierGenerator {

	@Override
	public Serializable generate(SharedSessionContractImplementor arg0, Object arg1) throws HibernateException {
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return "xzy_shop_book_" + sdf.format(new Date());
	}

}

在Worker.hbm.xml文件中打开<generator class="com.xzy.two.id.Myts" />这行注释代码