通过Hibernate从SQL数据库中获取随机对象 [英] Get random object from SQL database via Hibernate

问题描述

我有以下依赖MySql的代码（ORDER BY RAND（））。我想知道是否有Hibernate HQL替代它（管理员是布尔标签，表明用户作为管理员）。这是工作代码：

  public long getRandomAdmin（）{
 Session session = getSession（）; 
 Query selectQuery = session.createSQLQuery（SELECT user_id FROM users WHERE admin ='1 ORDER BY RAND（））; 
 selectQuery.setMaxResults（1）; 
 
列表< BigInteger> list = null; 
尝试{
 list = selectQuery.list（）; 
} catch（HibernateException e）{
 log.error（e）; 
抛出SessionFactoryUtils.convertHibernateAccessException（e）; 
 
 
 if（list.size（）！= 1）{
 log.debug（getRandomAdmin did not find any user）; 
返回0; 
} 
 log.debug（found：+ list.get（0））; 
 
 return list.get（0）.longValue（）; 
 
  

解决方案

查看此链接：
http：/ /www.shredzone.de/cilla/page/53/how-to-fetch-a-random-entry-with-hibernate.html

 标准限制= yourRestrictions; 
 Object result = null; //稍后将包含随机实体
 Criteria crit = session.createCriteria（Picture.class）; 
 crit.add（限制）; 
 crit.setProjection（Projections.rowCount（））; 
 int count =（（Number）crit.uniqueResult（））。intValue（）; 
 if（0！= count）{
 int index = new Random（）。nextInt（count）; 
 crit = session.createCriteria（Picture.class）; 
 crit.add（限制）; 
 result = crit.setFirstResult（index）.setMaxResults（1）.uniqueResult（）; 
} 
  

这就是你想要的。保持Hibernate作为一个抽象层，同时仍然能够查询一个随机对象。但是，性能会受到一些影响。

尽管我一直在使用Hibernate，但我不知道更简单易用的优雅方式。 Imho你应该将该方法包装在外观后面。

I have following MySql dependent code ( ORDER BY RAND() ) . I would like to know if there is hibernate HQL alternative for it (admin is boolean tag indicating that the user as an admin). This is working code:

public long getRandomAdmin() {
    Session session = getSession();
    Query selectQuery = session.createSQLQuery("SELECT user_id FROM users WHERE admin = '1' ORDER BY RAND()");
    selectQuery.setMaxResults(1);

    List<BigInteger> list = null;
    try {
        list = selectQuery.list();
    } catch (HibernateException e) {
        log.error(e);
        throw SessionFactoryUtils.convertHibernateAccessException(e);
    }

    if (list.size() != 1) {
        log.debug("getRandomAdmin didn't find any user");
        return 0;
    }
    log.debug("found: " + list.get(0));

    return list.get(0).longValue();
}

解决方案

See this link: http://www.shredzone.de/cilla/page/53/how-to-fetch-a-random-entry-with-hibernate.html

Criterion restriction = yourRestrictions;
Object result = null;  // will later contain a random entity
Criteria crit = session.createCriteria(Picture.class);
crit.add(restriction);
crit.setProjection(Projections.rowCount());
int count = ((Number) crit.uniqueResult()).intValue();
if (0 != count) {
  int index = new Random().nextInt(count);
  crit = session.createCriteria(Picture.class);
  crit.add(restriction);
  result = crit.setFirstResult(index).setMaxResults(1).uniqueResult();
}

This is what you want. Keep Hibernate as an abstraction layer while still being able to query a random object. Performance suffers a bit, though.

Although I've been using Hibernate a lot, I don't know a more elegant way that is easy to use. Imho you should wrap that method behind a facade.

这篇关于通过Hibernate从SQL数据库中获取随机对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！