Proper way to to handle null in getSingleResult aggregate

Question

is there any proper way to handle null for example there is no existing record in the Users table, so it wont throw null pointer:

`.getSingleResult()` should be only used for queries when **single** result is guaranteed. Not multiple result, not empty result, but **single**. Perfect example - count queries (`select count(...)`), they never return null or multiple result — Nikolai Shevchenko, Apr 23 '21 at 11:38

Yassin Hajaj · Answer 1 · 2021-04-23T12:45:55.910

2

If the record does not exist in the database, do not use getSingleResult(). Looking at the javadoc, you need to be sure the record exists to use getSingleResult()

getSingleResult

java.lang.Object getSingleResult()

Execute a SELECT query that returns a single untyped result.

Returns: the result

Throws:

NoResultException - if there is no result

NonUniqueResultException - if more than one result

Instead, use getResultList()

public long generateNextId() {
    Query query = getEntityManager().createQuery("SELECT MAX(id)+1 from Users");
    List<Object> objs = query.getResultList();
    return objs.isEmpty() ? 1 : Long.parseLong(objs.get(0));
}

Also, further, I'd use a TypedQuery<Long> if I were you

public long generateNextId() {
    TypedQuery<Long> query = getEntityManager().createQuery("SELECT MAX(id)+1 from Users", Long.class);
    List<Long> objs = query.getResultList();
    return objs.isEmpty() ? 1 : objs.get(0);
}

If, like documented in this question, the query can return null then you can just use a null check or use an Optional#ofNullable wrapper

edited Apr 23 '21 at 12:45

answered Apr 23 '21 at 09:47

Yassin Hajaj

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it seems query.getResultList() return size of 1 even there is no result in the query. – Apr 23 '21 at 10:13
Can you print the content of the list? – Yassin Hajaj Apr 23 '21 at 10:57
its kinda weird since, its not looping. but the arraysize is = 1. maybe because of the SELECT MAX aggregate? – Apr 23 '21 at 11:03
It is maybe because of the `+1` – Yassin Hajaj Apr 23 '21 at 11:03
I tried to remove. but its the same.. thats why its weird. I think the MAX is really returning null. – Apr 23 '21 at 11:48
That is very surprising to be honest :D – Yassin Hajaj Apr 23 '21 at 12:14
confirmed. List objs will have an element that is null. if SELECT MAX returns null. for example the table is empty. – Apr 23 '21 at 12:41
[Yes, that's true indeed @daniel.chan](https://stackoverflow.com/questions/1688715/select-maxx-is-returning-null-how-can-i-make-it-return-0) – Yassin Hajaj Apr 23 '21 at 12:44

Proper way to to handle null in getSingleResult aggregate

1 Answers1