Re: [IMPORTANT] Fetch-depth

[Craig L Russell]

Javadogs, Here's what I'm proposing, in summary.  1. Add a property to FetchPlan: get/setMaxFetchDepth. This property limits the depth of the fetched instance graph counting from the root of the instances. The roots are defined for queries as the results of the query. The roots of retrieve and detachCopy are the parameter instances. The default is 1, meaning fetch one level of objects reachable from the roots. A value of 0 has no meaning, because if a relationship field is in the fetch group, it will be fetched. 2. Add a property to FetchPlan: get/setDetachRoots. The roots for DetachAllOnCommit are all the instances in the DetachRoots on FetchPlan. The default is all instances in the cache. Or it could be all instances retrieved by queries, explicitly made persistent, or explicitly retrieved. 3. In order to avoid confusion, remove fetch-depth attribute for the field element and replace it with recursion-depth attribute. This has two effects: it requires users to change their metadata and think about what the fetch-depth was used for; and it better reflects the purpose of the attribute to limit recursion. The meaning of recursion-depth is the maximum number of links to follow from the target instance of this field in case the same class is encountered again.  4. In case of multiple definitions of the same field recursion-depth, the largest number for the same field will be used. That is, if the same field is declared in multiple fetch groups, a simple MAX of all the values is used. I'll write up a number of examples and send them tomorrow. Comments? Craig On Jan 13, 2006, at 3:10 PM, 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. 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! 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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