javax.persistence.NoResultException: No entity found for query

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.

Solution 1:

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..
}

Solution 2:

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);

Solution 3:

You mentioned getting the result list from the Query, since you don't know that there is a UniqueResult (hence the exception) you could use list and check the size?

if (query.list().size() == 1) 

Since you're not doing a get() to get your unique object a query will be executed whether you call uniqueResult or list.