Hello,
Imagine a dom. model like class A { @Id long id; String name; @Lazy B b;
}; class B { @Id String code; /* ... other attributes ... */ }.
When doing a Query on A with a FetchGroup that excludes the A's b field,
or simply through a @Lazy annotation, OpenJPA stills always loads the FK
(c.f.
http://openjpa.apache.org/builds/1.2.0/apache-openjpa-1.2.0/docs/manual/
ref_guide_fetch.html#ref_guide_fetch_impl
<http://openjpa.apache.org/builds/1.2.0/apache-openjpa-1.2.0/docs/manual
/ref_guide_fetch.html#ref_guide_fetch_impl> , "Even when a direct
relation is not eagerly fetched, OpenJPA selects the foreign key columns
and caches the values."), so the 'code' of B that is in the A table.
That's good.
Question: How do you now actually access/get the value of that b's code,
the String? OpenJPA has it, in memory, but when you hold an instance a
of A, the instant you do a.getB().getCode(), of course it will lazy load
the full B - because it has no way of knowing that after the getB()
you'll do only a getCode() ... ;-) I trust this has been considered and
thought of, and there is a solution... how???
I feel like I'm looking for "the opposite the
EntityManager.getReference() method", if that makes any sense? Is the
OpenJPAEntityManager's Object getObjectId(Object o) the rescue here...
but how exactly? A String bCode = oem.getObjectId(a.getB()) will most
likely still lead to a lazy DB load, right? Is there any chance
something like this: class A { ... @Lazy B b; B getB() { return this.b;
} String getBCodeId() { return HOWTOGETTHEEM.getObjectId(b); } } - will
work? Or will simply passing the b field to getObjectId also lead to a
lazy load? If that's feasible, how to get an EM inside the getter?
Much appreciate any ideas!
Regards,
Michael
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