How do I migrate my JPA DAO to Spring Data with second level cache? - spring

Question

I have bunch of JPA DAOs im looking to migrate to Spring Data JPA. Some of my DAOS have second-level / query caching set up.
I have a process where I only retrieve the ID in my queries, and then look up the entity using findByID(). This way, only the id's are multiplied in the different query caches, and the entire entities are in the second level cache.
Example:
#NamedQuery(name = "SystemUser.findByEmail",
query = "SELECT u.id FROM SystemUser u WHERE email=:email"),
…
public SystemUser findByEmail(String email) {
TypedQuery<Long> q = getEntityManager().createNamedQuery("SystemUser.findByEmail", Long.class);
q.setParameter("email", email);
q.setHint("org.hibernate.cacheable", true);
q.setHint("org.hibernate.cacheRegion", "query.systemUser");
List<Long> res = q.getResultList();
if (res != null && res.size() > 0) {
return findById(res.get(0));
}
return null;
}
I have several more findBy…-methods, all doing it like this. It feels like a good way to keep cache memory consumption down.
I'm kind of new to the Spring Data JPA business, but I can't see how I would go about realizing this here? The #Cacheable annotations seems only to deal with query caches, which to me would duplicate the entities in each query cache?
Is there any way to do this with Spring Data? Pointers would be much appreciated.

Answer 1

In Spring Data JPA just create a findByEmail method and either Spring Data JPA will found your named query or create one itself.
public class SystemUserRepository extends CrudRepository<SystemUser, Long> {
SystemUser findByEmail(String email);
}
Should be all you need to get the query executed and the desired result. Now with the #QueryHints you can add the hints you are setting now.
public class SystemUserRepository extends CrudRepository<SystemUser, Long> {
#QueryHints(
#QueryHint(name="org.hibernate.cacheable", value="true"),
#QueryHint(name="org.hibernate.cacheRegion", value="query.systemUser") )
SystemUser findByEmail(String email);
}
The result will be cached and still the user will come from the 2nd level cache (if available, else created). Assuming of course your entity is #Cacheable.
A nice read on how the 2 different caches work (together) can be found here. A small snippet on how the query cache works.
The query cache looks conceptually like an hash map where the key is composed by the query text and the parameter values, and the value is a list of entity Id's that match the query:
If you want more complex logic (and really implement the optimization you did) you can always implement your own repository.