Gremlin Groovy ClassCastException with Frames

Question

I'm receiving the following error while using the @GremlinGroovy annotation associated with tinkerpop's frames.

java.lang.ClassCastException: com.thinkaurelius.titan.graphdb.relations.CacheEdge cannot be cast to com.tinkerpop.blueprints.Vertex
    at com.tinkerpop.frames.structures.FramedVertexIterable$1.next(FramedVertexIterable.java:36)
    at com.tinkerpop.frames.annotations.gremlin.GremlinGroovyAnnotationHandler.processVertex(GremlinGroovyAnnotationHandler.java:75)
    at com.tinkerpop.frames.annotations.gremlin.GremlinGroovyAnnotationHandler.processElement(GremlinGroovyAnnotationHandler.java:114)
    at com.tinkerpop.frames.annotations.gremlin.GremlinGroovyAnnotationHandler.processElement(GremlinGroovyAnnotationHandler.java:30)
    at com.tinkerpop.frames.FramedElement.invoke(FramedElement.java:83)
    at com.sun.proxy.$Proxy81.getProxyCandidateEdgeFromPersonUuid(Unknown Source)
    at com.company.prod.domain.Person$Impl.toImpl(Person.java:100)
    ....

The following line causes the error:

FooEdge fe = foo.getFooEdgeFromUuid(this.getUuid());

Which is calling this method:

@GremlinGroovy("it.outE('has').filter{it.inV().has('uuid', T.eq, uuid).hasNext()}")
FooEdge getFooEdgeFromUuid(@GremlinParam("uuid") String uuid);

I've also tried the following traversal (which causes the same error):

@GremlinGroovy("it.out('has').has('uuid', T.eq, uuid).inE('has')")

However, when I open a gremlin shell to test out the same exact traversal - everything works out just fine. Any thoughts on what may be causing the issue?

Answer 1

This isn't as much of an answer as it is to a workaround. Instead of using the @GremlinGroovy annotation one can use gremlin with the @JavaHandler annotation.

@JavaHandler
void getFooEdgeFromUuid(String uuid);

abstract class Impl implements JavaHandlerContext<Vertex>, Foo {
    public FooEdge getFooEdgeFromUuid(String uuid) {
        return frameEdges(
                gremlin().out("has")
                        .has("person-uuid", Tokens.T.eq, uuid)
                        .inE("has"),
                FooEdge.class).iterator().next();
    }
}

Answer 2

I don't think you have proper usage there give the documentation on Frames for that annotation:

https://github.com/tinkerpop/frames/wiki/Gremlin-Groovy

First, note that both:

@GremlinGroovy("it.outE('has').filter{it.inV().has('uuid', T.eq, uuid).hasNext()}")
FooEdge getFooEdgeFromUuid(@GremlinParam("uuid") String uuid);

and:

@GremlinGroovy("it.out('has').has('uuid', T.eq, uuid).inE('has')")

returns an Iterator so that's not so helpful either as you would need to return some form of List in your getFooEdgeFromUuid() . Perhaps the appropriate thing to do, assuming you know for a fact that this query will only and always return one edge would be to do:

@GremlinGroovy("it.out('has').has('uuid', T.eq, uuid).inE('has').next()")

I say "always" because without that, you'll get yourself a NoSuchElementException otherwise. In that way, to align types properly, you could do:

@GremlinGroovy("it.outE('has').filter{it.inV().has('uuid', T.eq, uuid)}")
Iterable<FooEdge> getFooEdgesFromUuid(@GremlinParam("uuid") String uuid);

Of course, all that may not work, because of this sentence I see in the docs:

It is possible to make use of a Gremlin path expression as a means of determining vertex adjacency via the GremlinGroovyModule.

In other words, use of @GremlinGroovy is for returning framed vertices (and not edges as you are trying to do). If the approach I suggested above doesn't work then your workaround using the @JavaHandler may be your best option.