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Re: [eclipselink-users] Difference between cache-usage and maintain-cache query hints?
I'm interested to hear an answer to this question too.

I eventually just ended up caching the results in a application scoped bean, but that doesn't seem like the best solution to me.


Derek

On 11-03-16 04:27 PM, Laird Nelson wrote:
On Wed, Mar 16, 2011 at 4:10 PM, Laird Nelson <ljnelson@xxxxxxxxx> wrote:
My use case is the exceptionally brain-dead common example of caching a list of drop-down options.  The JPQL query in question is basically like one you'd write for U. S. states:

  SELECT s FROM State s ORDER BY s.code;

If I wanted this query to return results from the cache whenever possible, which of these two query hints should I use?  Or is there (preferably) a JPA-sanctioned query hint that would do the same thing?

Wow, it's even more complicated: http://www.eclipse.org/eclipselink/api/2.2/org/eclipse/persistence/config/QueryHints.html#QUERY_RESULTS_CACHE says, bafflingly:

Configures the query to use a results cache. By default the query will cache 100 query results, such that the same named query with the same arguments is re-executed it will skip the database and just return the cached results.

That part isn't baffling--that sounds like exactly what I want!  But then it goes on to say:

Valid values are: HintValues.PERSISTENCE_UNIT_DEFAULT, HintValues.TRUE, HintValues.FALSE, "" could be used instead of default value HintValues.PERSISTENCE_UNIT_DEFAULT. By default query results are not cached. This is not, and is independent from the object cache.

(This is not...what?)  What is the default?  Is it FALSE, or PERSISTENCE_UNIT_DEFAULT?  If this is the way to handle this use case, why is it not mentioned here: http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#How_to_Use_EclipseLink_JPA_Query_Hints?  Does this mean that I cannot use eclipselink.query-results-cache as a JPA query hint?  If I can, then why isn't it in the list of valid JPA query hints?

Benevolently confused,
Laird

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