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 none 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 throws 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.
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..
}
When using java 8, you may take advantage of stream API and simplify code to
return (YourEntityClass) entityManager.createQuery()
....
.getResultList()
.stream().findFirst();
That will give you java.util.Optional
If you prefer null instead, all you need is
...
.getResultList()
.stream().findFirst().orElse(null);
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