javax.persistence.NoResultException：找不到用于查询的实体 [英] javax.persistence.NoResultException: No entity found for query

问题描述

在我发布这个问题之前，我已经看过这个，但是我无法获得我正在寻找的东西。

我知道，对于我写的查询，可能只存在一行或根本不存在。所以，没有理由使用getResultList ....
这是我的代码

  String hql = from DrawUnusedBalance where unusedBalanceDate =：today; 
查询查询= em.createQuery（hql）; 
 query.setParameter（today，new LocalDate（））; 
 
 DrawUnusedBalance drawUnusedBalance = 
（DrawUnusedBalance）query.getSingleResult（）; //我们每天只能有一个
 //单个数据
 //`系统。 out.println（drawUnusedBalance.toString（））;`
  

问题是，如果没有行它会显示一个例外，如果没有，它可以正常工作。我知道这个问题，但我也在寻找最好的解决方案。

我想要的是，如果DB中没有行，我想获得一个空对象（而不是获取异常），所以我将插入一个新的数据。 ..如果它不是null ..我只是想更新它...

有一种方法来处理这个我认为是不正确的方式做它..它是..我会尝试catch块...如果它抛出一个异常我可以写入插入新的数据到数据块中的catch块...但我相信会有一个更好的方式...谢谢你的时间。

解决方案

是的。您需要使用 try / catch 块，但不需要捕获异常。 根据 API ，它将抛出 NoResultException 如果没有结果，并且由你决定如何处理它。

  DrawUnusedBalance drawUnusedBalance = null; 
 try {
 drawUnusedBalance =（DrawUnusedBalance）query.getSingleResult（）
 catch（NoResultException nre）{
 //忽略这一点，因为根据你的逻辑，这可以！ 
} 
 
 if（drawUnusedBalance == null）{
 //你的逻辑.. 
} 
  pre> 
Before I posted this question, I already looked this , but I couldn't get what I was looking for.

I know that for the query I wrote there may exist only one row or not at all. So, there is not reason for me to use getResultList .... 
Here is my code
String hql="from DrawUnusedBalance where unusedBalanceDate= :today";
Query query=em.createQuery(hql);
query.setParameter("today",new LocalDate());

DrawUnusedBalance drawUnusedBalance= 
    (DrawUnusedBalance)query.getSingleResult();//we can have only a
                                               // single datum per day
//`System.out.println(drawUnusedBalance.toString());`
The problem is, if there is no row, it shows an exception, and if not it works fine. I know the problem but I am also looking for the best solution. 

What I wanted is, if there is no row in the DB I wanted to get a null object (instead of getting an exception) so I will insert a new data ... if it is not null .. I just want to update it ... 

There is one way to handle this..which I believe is not the right way to do it .. It is .. I will have a try catch block ... and if it throws an exception I can write to insert new data in to the DB on the catch block ... But I believe there will be a better way ... Thank you for your time.
解决方案
Yes. You need to use the try/catch block, but no need to catch the Exception. As per the API it will throw NoResultException if there is no result, and its up to you how you want to handle it.
DrawUnusedBalance drawUnusedBalance = null;
try{
drawUnusedBalance = (DrawUnusedBalance)query.getSingleResult()
catch (NoResultException nre){
//Ignore this because as per your logic this is ok!
}

if(drawUnusedBalance == null){
 //Do your logic..
}


                        
这篇关于javax.persistence.NoResultException：找不到用于查询的实体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！