Hibernate / JPA处理空结果集

Question

I have a criteria builder which is defined as returning a Long. If the result set is empty, the whole application fails. How do I handle this to return a set number, eg 1000?

Long yesterday = new Long(0);

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Long> q = cb.createQuery(Long.class);
Root<CustomerHistory> hist = q.from(CustomerHistory.class);

q.multiselect(hist.get("total"));
Date yesterDate = new LocalDate().minusDays(1).toDateTimeAtStartOfDay().toDate();

Predicate w1 = cb.equal(hist.<Date>get("date"), yesterDate);
Predicate w2 = cb.equal(hist.get("customer"), customer);
q.where(w1,w2);

yesterday = em.createQuery(q).getSingleResult();


return yesterday < tot;

Answer 1

If there is an empty resultset, the Query.getSingleResult() throws a javax.persistence.NoResultException which is a RuntimeException . You are free to catch it in a try-catch block and handle it from there.

To set the maximum amount of result set, call the Query.setMaximumResults(int maxResult) and call the getResultList() (which returns a List of the entity desired).

Answer 2

From JPA API

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

Consider catch the Exception of NoResultException and continue with the logic