java学习：Hibernate学习用oracle sequence序列生成ID的配置示例

接上回继续，TMP_EMP中的ID是根据序列SQ_TMP_EMP来生成的，需要在TmpEmp.hbm.xml中设置：

  <id name="id" type="long">
   <column name="ID" not-null="true" sql-type="NUMBER" unique="true"/>
   <generator class="sequence">
    <param name="sequence">SQ_TMP_EMP</param>   
   </generator>
  </id>

这样运行时，Hibernate就会自动从SQ_TMP_EMP中取nextval用来填充到ID字段中

示例代码：

先创建一个工具类

package app;

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

public class HibernateUtils {
	
	private HibernateUtils(){
		
	}
	
	static SessionFactory sessionFactory;
	
	/*
	 * 取得Hibernate的Session
	 */
	public static Session getSession(){
		if (sessionFactory == null) {
			sessionFactory = new Configuration().configure().buildSessionFactory();
		}
		return sessionFactory.openSession();
	}
	
	
	/*
	 * insert记录
	 */
	public static  boolean addObject(Object obj){
		Session ss = null;
		Transaction ts = null;
		boolean result = false;
		try		
		{
			ss = getSession();
			ts = ss.beginTransaction();
			ss.save(obj);
			ts.commit();
			result = true;
		}
		finally{
			ss.close();
		}		
		return result;
		
	}

}

添加记录的类

package app;

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

import java.math.BigDecimal;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

public class Hello {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		TmpEmp emp = new TmpEmp();
		emp.setName("张三峰");
		emp.setSalary(new BigDecimal(1000));
		emp.setSex('M');		
		emp.setBirthday(new Date(1985-1900,12-1,1));//1985-12-1号
		boolean b = HibernateUtils.addObject(emp);
		if (b){
			System.out.println("插入成功，新记录的ID是：" + emp.getId());
		}
		else{
			System.out.println("插入失败!");
		}
		
	}

	

}

运行结果:

Hibernate: select IGSA.SQ_TMP_EMP.nextval from dual
Hibernate: insert into IGSA.TMP_EMP (NAME, BIRTHDAY, SEX, SALARY, ID) values (?, ?, ?, ?, ?)
插入成功，新记录的ID是：210　　

当然，除用.hbm.xml来配置外，等效的注解方式，可以参考下面的写法：

    @Id    
    @SequenceGenerator(name="bkdex_seq_generator",sequenceName="SQ_BKD_EX")
    @GeneratedValue(generator="bkdex_seq_generator",strategy=GenerationType.SEQUENCE)
    @Column(name = "ID", unique = true, nullable = false, precision = 22, scale = 0)
    public BigDecimal getId() {
        return this.id;
    }

基本上这样就行了，但是实际运行会发现sequence每次并不是加1，而是一个其它的数，如果想要每次加1，参考下面这样：

    @Id
    @SequenceGenerator(name = "SEQ_ORDER", sequenceName = "SEQ_ORDER", allocationSize = 1)
    @GeneratedValue(generator = "SEQ_ORDER", strategy = GenerationType.SEQUENCE)
    @Column(name = "ID", unique = true, nullable = false, precision = 22, scale = 0)
    public BigDecimal getId() {
        return this.id;
    }

allocationSize=1 这个是关键