JPA/HIBERNATE - Are objects instances cached indexed just by id ?

Question

Probably it is a basic question, but could not found the answer anywhere in the web.

I am trying to use a second level cache (using ehcache) and just checked that some objects were being retrieved from database every time I tried to load them, the only difference was that I was not getting them by id but by a property that carries a SEO friendly name that are used to create urls on the system I am working. Is jpa/hibernate able to retrieve objects from cache just by with the id of the obj? Is there any way to get it working without need to activate the query cache?

Answer 1

Is jpa/hibernate able to retrieve objects from cache just by with the id of the obj?

Yes, the second level cache works for query that looks for a single object based on Id i.e. when using EntityManager.find() or EntityManager.getReference() (or the equivalent Session#get() and Session#load() from the Hibernate API). AFAIK, this applies to all JPA implementations.

Is there any way to get it working without need to activate the query cache?

With standard JPA, I don't see any other option than using the Query Cache.

But if you don't mind using Hibernate API, there might be an alternative with Query#iterate(). With Query#iterate(), Hibernate will issue a SQL query that will fetch only the IDs and when you iterate over the results, it will load the corresponding entities from the cache.

Obviously, Query#iterate() will be much slower than Query#list() if you're not using a second level cache.

Personally, I'd use the query cache.

See also

• Hibernate: Truly Understanding the Second-Level and Query Caches