Hibernate中使用load和get加载的区别
2021-07-20 10:05
标签：null dtd .config uil logs 取数 数据库 size private 一. Hibernate使用load机制和使用get加载的区别(重点) 1.相同点：get 和load他们都可以通过指定的实体类与ID从数据库中读取数据,并返回对应的实例 2. 不同点：如果找不到符合条件的纪录，get()方法将返回null．而load()将会报出ObjectNotFoundEcception． 2.1get 是直接从数据库中检索 而load会使用懒加载（延迟加载）产生一个代理对象，属性oid 2.2 使用load加载，Hibernate会认为该id对应的对象是一定存在的，所以它可以放心的使用，它可以放心的使用代理来 延迟加载该对象。在用到对象中的其他属性数据时才查询数据库，但是万一数据库中不存在该记录，那没办法，只能抛异常。 2.3 使用get加载，hibernate会确认一下该id对应的数据是否存在，首先在session缓存中查找，然后在二级缓存中查找，还没有就查数据库，数据库中没有就返回null。 3.测试代码如下： 3.1创建Hibernate的主配置文件： 3.2 创建hibernate的隐射文件Emp.hbm.xml 3.3创建Emp表的实体类 3.4 创建测试类代码： Hibernate中使用load和get加载的区别 标签：null dtd .config uil logs 取数 数据库 size private 原文地址：http://www.cnblogs.com/xushirong/p/7056133.htmlxml version=‘1.0‘ encoding=‘UTF-8‘?>
DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
hibernate-configuration>
session-factory>
property name="dialect">org.hibernate.dialect.Oracle9Dialectproperty>
property name="connection.url">jdbc:oracle:thin:local:1521:orclproperty>
property name="connection.username">scottproperty>
property name="connection.password">tigerproperty>
property name="connection.driver_class">oracle.jdbc.OracleDriverproperty>
property name="show_sql">trueproperty>
mapping resource="cn/et/hibernate/lesson02/query/Emp.hbm.xml" />
session-factory>
hibernate-configuration>
xml version="1.0" encoding="utf-8"?>
DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
hibernate-mapping>
class name="cn.et.hibernate.lesson01.Emp" table="EMP" schema="SCOTT">
id name="empno" type="java.lang.Short">
column name="EMPNO"/>
generator class="native" />
id>
property name="ename" type="java.lang.String">
column name="ENAME">
comment>员工姓名comment>
column>
property>
property name="job" type="java.lang.String">
column name="JOB">
comment>员工职位comment>
column>
property>
property name="mgr" type="java.lang.Short">
column name="MGR">
comment>领导编号comment>
column>
property>
property name="hiredate" type="java.util.Date">
column name="HIREDATE">
comment>雇佣日期comment>
column>
property>
property name="sal" type="java.lang.Double">
column name="SAL">
comment>月薪comment>
column>
property>
property name="comm" type="java.lang.Double">
column name="COMM">
comment>奖金comment>
column>
property>
property name="deptno" type="java.lang.Short">
column name="DEPTNO">
comment>所属部门编号comment>
column>
property>
class>
hibernate-mapping>
package cn.et.hibernate.lesson02.query;
import java.util.Date;
/**
* Emp entity. @author MyEclipse Persistence Tools
*/
public class Emp implements java.io.Serializable {
// Fields
private Short empno;
private String ename;
private String job;
private Short mgr;
private Date hiredate;
private Double sal;
private Double comm;
private Short deptno;
// Constructors
/** default constructor */
public Emp() {
}
/** full constructor */
public Emp(String ename, String job, Short mgr, Date hiredate, Double sal,
Double comm, Short deptno) {
this.ename = ename;
this.job = job;
this.mgr = mgr;
this.hiredate = hiredate;
this.sal = sal;
this.comm = comm;
this.deptno = deptno;
}
// Property accessors
public Short getEmpno() {
return this.empno;
}
public void setEmpno(Short empno) {
this.empno = empno;
}
public String getEname() {
return this.ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public String getJob() {
return this.job;
}
public void setJob(String job) {
this.job = job;
}
public Short getMgr() {
return this.mgr;
}
public void setMgr(Short mgr) {
this.mgr = mgr;
}
public Date getHiredate() {
return this.hiredate;
}
public void setHiredate(Date hiredate) {
this.hiredate = hiredate;
}
public Double getSal() {
return this.sal;
}
public void setSal(Double sal) {
this.sal = sal;
}
public Double getComm() {
return this.comm;
}
public void setComm(Double comm) {
this.comm = comm;
}
public Short getDeptno() {
return this.deptno;
}
public void setDeptno(Short deptno) {
this.deptno = deptno;
}
}
package cn.et.hibernate.lesson02.query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class TestHibernate {
//表示增加
@Test
public void test1(){
//创建sessionFactory
SessionFactory sf = new Configuration().configure("/cn/et/hibernate/lesson02/hibernate.cfg.xml").buildSessionFactory();
Session session = sf.openSession();
//开启一个事物
Transaction t = session.beginTransaction();
Emp emp = (Emp)session.load(Emp.class,Short.parseShort("7369"));
t.commit();
}
}
//上述代码可用dubug模式进行调试，加载load 和get ，测试加载的过程