i am trying to reuse a dynamic query as a named query as described here:
https://wiki.eclipse.org/EclipseLink/Release/2.5/JPA21#Add_Named_Query
the goal is to build the criteria-query only once and then reuse it as a namedquery if parameter did not change.
public static List<User>getUserByParameter(ParameterMap parameter){
EntityManager em = getEntityManager();
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<User> criteriaQuery = builder.createQuery(User.class);
Root<User> user = criteriaQuery.from(User.class);
List<Predicate> predicates = new ArrayList<Predicate>();
//...build up the query depending on parameter
if (null != parameter.getStatus()){
predicates.add(builder.equal(user.<Integer>get("status"), parameter.getStatus()));
}
//etc.
criteriaQuery.select(user).where(predicates.toArray(new Predicate[]{}));
Query query = em.createQuery(criteriaQuery);
//now register this query as a namedQuery
em.getEntityManagerFactory().addNamedQuery("userByParameter", query);
return query.getResultList();
}
i thought about something like:
public static List<User>getUserByParameter(ParameterMap parameter){
Query userByParameter = em.createNamedQuery("userByParameter");
if (null != userByParameter){
return userByParameter.getResultList();
}else {
//build the dynamic query as above
}
}
this results in a nullpointer as the namedQuery doesn't exist the first time.
how can i reuse the query in the same method or in other words, how can i check in a clean way (without using try-catch) if a namedquery exists?
