How to check if a record exists using JPA

Question

I want to know whether a given record is present in a database or not. so far I have achieved this by writing a JPA query and the running it by getSingleResult() method. this would throw a NoResultException if the record with the given parameter does not exist. Of course, it's not a must for the record to exist, so it's the normal behaviour sometimes, that's why I asked to myself, is it neccessary to throw an Exception which I have to handle by a catch block? As far as I know the cost of Exception handling is quite big, so I'm not very satisfied with this solution, also, I don't even need the object, I only need to know it's existence in the DB.

Is there a better way to check whether an object exist or not? eg. using getResultList() and checking it's size maybe?

Answer 1

If you just want to know whether the object exists, send a SELECT COUNT to your database. That will return 0 or 1.

The cost of the exception handling isn't that big (unless you do that millions of times during a normal operation), so I wouldn't bother.

But the code doesn't really reflect your intention. Since getSingleResult() calls getResultList() internally, it's clearer like so:

public boolean objExists(...) {     return getResultList(...).size() == 1; } 

If you query by object id and you have caching enabled, that will become a simple lookup in the cache if the object has already been loaded.

Answer 2

Try to avoid loading the entity into the session (getSingleResult()) just to check for it's existence. A count is better here. With the Criteria Query API it would look something like this:

public <E extends AbstractEntity> boolean exists(final Class<E> entityClass, final int id) {     final EntityManager em = getEntityManager();     final CriteriaBuilder cb = em.getCriteriaBuilder();      final CriteriaQuery<Long> cq = cb.createQuery(Long.class);     final Root<E> from = cq.from(entityClass);      cq.select(cb.count(from));     cq.where(cb.equal(from.get(AbstractEntity_.id), id));      final TypedQuery<Long> tq = em.createQuery(cq);     return tq.getSingleResult() > 0; }