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From Jörg von Frantzius <joerg.von.frantz...@artnology.com>
Subject Re: [IMPORTANT] Fetch-depth
Date Mon, 16 Jan 2006 16:13:23 GMT
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:Craig.Russell@sun.com
>> P.S. A good JDO? O, Gasp!

Dipl.-Inf. Jörg von Frantzius  |            artnology GmbH
                               |                Milastr. 4
Tel +49 (0)30 4435 099 26      |              10437 Berlin
Fax +49 (0)30 4435 099 99      |  http://www.artnology.com

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