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From "Frank D." <wii...@yahoo.co.uk>
Subject Retrieving data from Lookup Tables
Date Mon, 22 Sep 2008 15:52:26 GMT

Planning to use OpenJPA in a new application development and am spending some
time to review options of how it could be implemented.

I hope to use the rich domain model that has has already been developed for
the application.  This model implements a lookup object that has a few
attributes  (lookUpType, lookUpValue, sortOrder, disabled).

In the domain model, any lookup is mapped as a one-to-many relationship from
the main object to the lookup object.  In the database model, these will be
implemented as foreign key lookups to a lookup table.

Pre JPA and Hibernate, if using hand coded SQL, I would read these foreign
keys as int/long and then resolve to their values using a pre-initialised
cache. (for performance etc.).

Using OpenJPA, the default mechanism would load the lookup objects from the
LookUp table either eagerly when the main object is read from the database,
of lazily when the lookup is accessed.  Neither seems like a good solution
from a performance point of view.  The eager load strategy would create a
large SQL statement with multiple joins to the LookUp table (there could be
multiple lookups in the main object).  The lazy load strategy would cause
multiple individual SQL statements when the lookup objects were referenced.

I have not had a chance to do much experimentation - from reading it looks
like there may be some ways to optimise using a combination of pinning all
the lookup objects into cache, loading of the main object with a lazy load
strategy for the lookup objects, and then specifically referencing all of
the lookups  so that they are retrieved by JPA (from the cache) - possibly
with the use of a fetch group.  This sounds like a lot of overhead
(performance and developer) for a simple problem.

Since this seems to be a common design issue so I assume someone more
experienced than me has come up with a good solution.

Can anybody help?

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