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hibernate查询某一个对象后,执行createSQLQuery查询出现的问题

2014-10-31 10:20 791 查看
最近工作中碰到了一个奇怪问题,特别做下笔记:

user表里的数据,是1,1和2,2,分别为id和name字段。

代码如下:

import org.hibernate.Hibernate;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

public class Test {

private static final SessionFactory sessionFactory;

static {

try {

// Create the SessionFactory from hibernate.cfg.xml

sessionFactory = new Configuration().configure().buildSessionFactory();

} catch (Throwable ex) {

// Make sure you log the exception, as it might be swallowed

System.err.println("Initial SessionFactory creation failed." + ex);

throw new ExceptionInInitializerError(ex);

}

}

public static SessionFactory getSessionFactory() {

return sessionFactory;

}

public static void main(String[] args) {

Session session = sessionFactory.openSession();

Transaction tr = session.beginTransaction();

tr.begin();

User user = (User) session.load(User.class, 1);

user.setName("2");

session.saveOrUpdate(user);

int num = (Integer) session.createSQLQuery("select count(*) num from user where name = 2 ").addScalar("num", Hibernate.INTEGER).uniqueResult();

System.out.println(num);

tr.commit();

}

打印结果:

Hibernate: select user0_.id as id0_0_, user0_.name as name0_0_ from user user0_ where user0_.id=?

Hibernate: select count(*) num from user where name = 2

1

Hibernate: update user set name=? where id=?

也就是说通过session.createSQLQuery这个方法并没有先去更新user对象,所以结果还是1,而我想要的结果是2,所以会出现这样错误

修改代码 :

import org.hibernate.Hibernate;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

public class Test {

private static final SessionFactory sessionFactory;

static {

try {

// Create the SessionFactory from hibernate.cfg.xml

sessionFactory = new Configuration().configure().buildSessionFactory();

} catch (Throwable ex) {

// Make sure you log the exception, as it might be swallowed

System.err.println("Initial SessionFactory creation failed." + ex);

throw new ExceptionInInitializerError(ex);

}

}

public static SessionFactory getSessionFactory() {

return sessionFactory;

}

public static void main(String[] args) {

Session session = sessionFactory.openSession();

Transaction tr = session.beginTransaction();

tr.begin();

User user = (User) session.load(User.class, 1);

user.setName("2");

session.saveOrUpdate(user);

int num = (Integer) session.createQuery("from User where name = 2 ").list().size();

System.out.println(num);

tr.commit();

}

}

执行结果:

Hibernate: select user0_.id as id0_0_, user0_.name as name0_0_ from user user0_ where user0_.id=?

Hibernate: update user set name=? where id=?

Hibernate: select user0_.id as id0_, user0_.name as name0_ from user user0_ where user0_.name=2

2

这里就是先更新了user对象后,再来查询了,所以这种情况是正确的

总结:如果跟新了查出来的对象,saveorupdate了,然后用session.createSQLQuery方法的时候,也是查询不到修改的对象的,从打印语句可以看出来:

先查询了,然后再更新了哦,所以会出现问题的
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