What is the correct way to obtain TraversalDescription? - spring-data-neo4j

Question

I am using SpringRestGraphDatabase, SDN 3.1.0 and neo4j 2.1.2.
I am struggling to find the way how to obtain TraversalDescription instance.
I see that TraversalDescription traversalDescription = Traversal.description() is deprecated.
But this works!
Other way suggested elsewhere:
TraversalDescription traversalDescription = new TraversalDescriptionImpl();
does not work since TraversalDescriptionImpl is removed from neo4j 2.x
The third way suggested in neo4j user guide is through GraphDatabaseService:
TraversalDescription traversalDescription = graphDatabaseService.traversalDescription()
but then I am getting:
Caused by: java.lang.UnsupportedOperationException: Only builtin paths supported
at org.neo4j.rest.graphdb.traversal.RestTraversal.evaluator(RestTraversal.java:96)
Any ideas?
Thanks,
Milan

Answer 1

traversalDescription = graphDatabaseService.traversalDescription()
is indeed the correct way to obtain a TraversalDescription() in neo4j 2.x (either embedded or REST).
The problem indicated in the message you're getting is not that you're unable to obtain a TraversalDescription, and in fact it confirms that you are obtaining one, but are then trying to do an UnsupportedOperation with it.
Without seeing more of your code, I can't tell you what that is, but check out the relevant source code (github):
public RestTraversalDescription filter(Predicate<Path> pathPredicate) {
if (pathPredicate == Evaluators.all()) return add("return_filter",toMap("language","builtin", "name","all"));
if (pathPredicate == Evaluators.excludeStartPosition()) return add("return_filter",toMap("language","builtin", "name","all_but_start_node"));
throw new UnsupportedOperationException("Only builtin paths supported");
}
public RestTraversalDescription evaluator(PathEvaluator evaluator) {
if (evaluator == Evaluators.all()) return add("return_filter",toMap("language","builtin", "name","all"));
if (evaluator == Evaluators.excludeStartPosition()) return add("return_filter",toMap("language","builtin", "name","all_but_start_node"));
throw new UnsupportedOperationException("Only builtin paths supported");
}
public RestTraversalDescription evaluator(Evaluator evaluator) {
if (evaluator == Evaluators.all()) return add("return_filter",toMap("language","builtin", "name","all"));
if (evaluator == Evaluators.excludeStartPosition()) return add("return_filter",toMap("language","builtin", "name","all_but_start_node"));
throw new UnsupportedOperationException("Only builtin paths supported");
}
You'll know which of these methods specifically is throwing the exception based on the parameter you're passing in (or you could look at the line number given in the stack trace), then alter your implementation to make sure one of the if's evaluates to true so the throw doesn't get reached.