JPA getSingleResult() or null

Question

Throwing an exception is how getSingleResult() indicates it can't be found. Personally I can't stand this kind of API. It forces spurious exception handling for no real benefit. You just have to wrap the code in a try-catch block.

Alternatively you can query for a list and see if its empty. That doesn't throw an exception. Actually since you're not doing a primary key lookup technically there could be multiple results (even if one, both or the combination of your foreign keys or constraints makes this impossible in practice) so this is probably the more appropriate solution.

I encapsulated the logic in the following helper method.

public class JpaResultHelper {
    public static Object getSingleResultOrNull(Query query){
        List results = query.getResultList();
        if (results.isEmpty()) return null;
        else if (results.size() == 1) return results.get(0);
        throw new NonUniqueResultException();
    }
}

Try this in Java 8:

Optional first = query.getResultList().stream().findFirst();

Here's a good option for doing this:

public static <T> T getSingleResult(TypedQuery<T> query) {
    query.setMaxResults(1);
    List<T> list = query.getResultList();
    if (list == null || list.isEmpty()) {
        return null;
    }

    return list.get(0);
}

Spring has a utility method for this:

TypedQuery<Profile> query = em.createNamedQuery(namedQuery, Profile.class);
...
return org.springframework.dao.support.DataAccessUtils.singleResult(query.getResultList());

I've done (in Java 8):

query.getResultList().stream().findFirst().orElse(null);

From JPA 2.2, instead of .getResultList() and checking if list is empty or creating a stream you can return stream and take first element.

.getResultStream()
.findFirst()
.orElse(null);