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From "Dan Connelly (JIRA)" <j...@apache.org>
Subject [jira] Created: (GRFT-106) Avoid INFINITE RECURSION when Object Model has cycles.
Date Sun, 24 Sep 2006 12:56:22 GMT
Avoid INFINITE RECURSION when Object Model has cycles.
------------------------------------------------------

                 Key: GRFT-106
                 URL: http://issues.apache.org/jira/browse/GRFT-106
             Project: Graffito
          Issue Type: Improvement
          Components: JCR-Mapping
            Reporter: Dan Connelly
            Priority: Critical


The default ObjectConverterImpl is restricted to acyclic graphs in the object model.

Many Java object models are NOT acyclic.   For instance, I am on your Friends list.   Yoar
are on my Friends list.     Java encourages such structures.   Almost any large object model
in Java will have hidden cycles.

Saving an Object Model that contains cycles using Graffito causes an infinite recursion.

Clearly, it is important to maintain a 1-to-1 correspondence between Nodes and Objects to
prevent this.   In the absence of Multiple Parent Nodes, it will be necessary to use REFERENCE
or UNDEFINED Items in place of the 2nd (or greater) Node representing a given Object.   My
preference si that the default ObjectConverterImpl should support REFERENCE.,    Failing this,
use of UNDEFINED also solves this problem and would  acceptable (as default).  Whether or
not REFERENCE is used, both insertion and retrieval must provide a reasonable result.   A
custom ojbect converter should be available to switch UNDEFINED to REFERENCE, or vice versa.

Also, it is probably best to keep the targeted, well-defined Nodes close to the Root Node.
   This implies that the default ObjectConverterImpl should implement a Breadth-First, rather
than a Depth-First, traversal of the Object Model on both insertion and retrieval.   Again,
if the default is Depth-First, a custom object converter should be available that implements
Breadth-First.

Admittedly, support for (2 representations) X (2 traversals) implies a drastic refactoring
and/or rewriting of the ObjectConverterImpl class.

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