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From Andy Jefferson <a...@datanucleus.org>
Subject Re: Fetch configuration
Date Wed, 14 Jul 2010 09:37:35 GMT
Post from 25 August 2008 by Craig.

> http://openjpa.apache.org/docs/latest/manual/manual.html#ref_guide_fetch_im
> pl says that "Even when a direct relation is not eagerly fetched,
> OpenJPA selects the foreign key columns and caches the values. This way
> when you do traverse the relation, OpenJPA can often find the related
> object in its cache, or at least avoid joins when loading the related
> object from the database." - that's very kind, but may be we have an
> Entity with lots of foreign key columns and I KNOW I only want a list
> showing a few attributes, and I KNOW that the direct relations won't be
> traversed (say because the Entites are detached, may be). Is there any
> way to configure OpenJPA to NOT eagerly fetch direct relations, unless
> they are explicitly part of the Fetch Group? Actually what I'd want is
> to be able to by default not include foreign key columns, but have a way
> to explicitly include them - which is not the same as having the field
> as part of the FetchGroup (that will lead to a JOIN, I may just want to
> control whether or not to selects the foreign key column).
> 
> Currently we don't have the notion in JDO of fetching key values of
> relationships, just fetching the targets of these keys.
> Would it be useful to consider adding to the JDO specification the
> ability to specify fetching the keys for relationships and not the
> relationships themselves? This would probably include adding some
> metadata to fetch-group and to FetchGroup.

Just seen a need for this also, bit late I know ;-)
Perhaps add something in JDO3.1 ?


-- 
Andy
DataNucleus (http://www.datanucleus.org)

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