2011/1/3 Anders Nawroth <[email protected]>
> Hi!
>
> When using TraversalDescription.evaluator(), are there any guarantees
> regarding in which order the evaluators will be executed?
>
In the same order they were added
>
> My use case is that I have a base TraversalDescription which excludes
> the start position using Evaluators.excludeStartPosition(). Then I
> discovered that other TraversalDescriptions built from this one still
> need to take care of evaluating the start position.
>
> This fact was hidden because of that the traversal didn't throw any
> expection when invoking methods on the last relationship traversed, even
> when the last releationship was in fact null. (I checked that my code
> actually throws a NPE ... but the traverser swallows that one.)
>
I just tried it and my exceptions thrown from an Evaluator gets propagated
correctly:
Evaluator e1 = new Evaluator() {
public Evaluation evaluate( Path path ) {
return Evaluation.INCLUDE_AND_CONTINUE;
}
};
Evaluator e2 = new Evaluator() {
public Evaluation evaluate( Path path ) {
throw new RuntimeException();
}
};
IteratorUtil.lastOrNull( Traversal.description().evaluator( e1
).evaluator( e2 ).traverse( db.getReferenceNode() ) );
Is there any way you could provide code here to trigger that case?
>
> I just don't like having to take care of the start position special case
> in each evaluator - is there any nice way I can avoid this?
>
I see your point, but if there are multiple evaluators they will be invoked
up until both PRUNE _and_ EXCLUDE have been returned. Then it can be certain
that it doesn't need to ask any other evaluator. Up until then evaluators
have to be invoked.
>
> /anders
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--
Mattias Persson, [[email protected]]
Hacker, Neo Technology
www.neotechnology.com
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