Thank you Alexander, I hadn't been watching!
Alexander Bieber schrieb:
Thanks Craig for taking our arguments into account.
I'll still have a comment concerning the use case Jörg von Frantzuis
submitted. His case is to limit the object-plan depth to a certain
level while using FetchPlan.ALL as fetch-group. This is used for
synchronizing data between datastores generically. In my oppinion we
should think of an additional and optional (defaulting to -1)
parameter to detachCopy - detachDepth - for this case.
If fetch-depth is meant to limit recursion (or if it would more
accurately be renamed to "recursion-depth", see below), then there would
be no way anymore of determining the fetch-depth absolutely when
detaching. As Alexander said, my usecase depends on that and my code
would break. If anyone is interested to know why synchronizing two
different databases in a generic way depends on that, then I'll be happy
to elaborate further.
I'd be equally happy with a fetchDepth parameter to PM.detachCopy(), as
Alexander proposes.
Best regards
Alexander Bieber
Craig L Russell wrote:
Javadogs,
I've spent some time looking at the semantics of fetch-depth and now
agree with the critics of the change that I proposed back in the
infamous October 1, 2005 message to the expert group subject: *Re:
JDO2 §12.7.2: fetch-depth only for "recursive fetch group references"?*.
I now believe it's impractical to use fetch-depth to mean the maximum
depth of the object graph reachable from the root object(s) field
because of several messages sent on the subject by Joerg von
Frantzuis, Alexander Bieber, and Marco Schultz.
Briefly, the argument is that if fetch-depth limits the number
absolutely, then it's not possible easily to use the fetch-group to
add another field to a fetch plan simply by adding a fetch-group that
includes that field. Instead, a new fetch-group that changes the
fetch-depth must be used. And each new use-case needs to provide a
different fetch-depth number if another level of fetching is desired.
I believe that the use of fetch-group to determine whether fields
(navigating relationships) are fetched should be natural, and that we
should therefore use fetch-depth for its original purpose of limiting
recursion.
Two remarks if we want to limit recursion:
1. It shouldn't be called "fetch-depth" but "recursion-depth",
because that's what it is then (it does not determine the actual
number of fetches!)
2. It should be clearly defined what kind of recursion is meant here,
i.e. by class or by object. I remember it being agreed that by
object is the most useful.
If you disagree with this position, please reply so we can move
forward and define the use of fetch-depth for recursion (as in the
original semantics of the attribute).
Thanks,
Craig
Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
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