First off, IMHO it is absolutely useful to have a feature for
discovering cycles in the object-graph while detaching, and stopping the
detaching there. This is not achievable by simply applying fetch-groups
that define some fetch-depth (at least not in any reasonable generic form),
Marco Schulze wrote:
Now, we first imagine, we have a "recursion-depth" available. This
"recursion-depth" is not counted relative to the absolute root of the
object graph (like the fetch-depth), but only when the same field of the
same class is recursively passed by the detach-process. In order to give
the client the maximal flexibility to get object graphs shaped in
whatever form he wants, we simply need the following fetch-groups:
[..]
All of these fetch-groups would be declared with fetch-depth=0 and
recursion-depth=1.
After having thought about it for a while, I started to doubt whether we
really need a "recursion-depth" number here. Can you think of a case
where you'd need any value greater than 1 here?
Also, I don't think it should really be the same field of the same class
to be reached to count a cycle, but it should rather be just the same
class that is reached. In the example given it's not a problem, but
there are other thinkable object models where you'd probably fetch too
much if you don't stop in the same class being reached again.
So I'd rather call this a boolean flag "recurse-class-cycles".
* Make "fetch-depth" to what I named "recursion-depth" as can
already be understood from the current spec.
Craig had clarified this possible misunderstanding in his mail 'Re: JDO2
§12.7.2: fetch-depth only for "recursive fetch group references"?'. It's
probably going to have a different wording in the next release of the
spec to prevent "fetch-depth" from being understood as some kind of
cycle-detection.
Then it would of
course be necessary to add a maximum fetch-depth to either the
detachCopy method or to the fetch plan.
I can't see why the spec should be changed for this rather than
extended. Your requirement for a cycle-detection probably doesn't
invalidate existing requirements for an absolute fetch-depth.
--
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