Avoid INFINITE RECURSION when Object Model has cycles.
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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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