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:
1 Answers
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
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