[TINKERPOP-2510] by-modulator throws when token is used after elementMap()

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.4.9
• Component/s: process
• Assignee: Unassigned
• Reporter: Christopher Smith
• Created: 26/Jan/21 04:59
• Updated: 26/Jan/21 14:50

Description

I'm attempting to write a "join" traversal to return the values of several related vertices (of different types), starting from an entry vertex. In order to extract the relevant properties, I am currently using elementMap, then trying to stash the vertex properties to continue with my query:

gts.V(entryPoint).as('p')
  .sideEffect(__.elementMap().group('pp').by(T.id))
  .out...
  ...
  .select('pp', ...)

As elementMap produces a map that includes the tokens as map keys, I expected by(T.id) to extract a map keyed on the vertex ID with the properties as the value (right now folded, but I'm crunching on that later). Using strings like 'firstName' works as expected, but of course using the string 'id' does not because the map key is the token, not the string.

However, passing T.id to the by-modulator when the value is a map (instead of an element) produces a ClassCastException. As far as I can tell, the processor is assuming somewhere that by(T.id) indicates that the incoming value is an element, which (at least after the addition of elementMap) is not true.

java.lang.ClassCastException: class java.util.LinkedHashMap cannot be cast to class org.apache.tinkerpop.gremlin.structure.Element (java.util.LinkedHashMap is in module java.base of loader 'bootstrap'; org.apache.tinkerpop.gremlin.structure.Element is in unnamed module of loader 'app')
	at org.apache.tinkerpop.gremlin.process.traversal.lambda.TokenTraversal.addStart(TokenTraversal.java:46)
	at org.apache.tinkerpop.gremlin.process.traversal.util.TraversalUtil.apply(TraversalUtil.java:42)
	at org.apache.tinkerpop.gremlin.process.traversal.util.TraversalUtil.applyNullable(TraversalUtil.java:87)
	at org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.GroupSideEffectStep.sideEffect(GroupSideEffectStep.java:114)
	at org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.SideEffectStep.processNextStart(SideEffectStep.java:39)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversal.hasNext(DefaultTraversal.java:197)
	at org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.TraversalSideEffectStep.sideEffect(TraversalSideEffectStep.java:48)
	at org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.SideEffectStep.processNextStart(SideEffectStep.java:39)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.FlatMapStep.processNextStart(FlatMapStep.java:48)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.filter.FilterStep.processNextStart(FilterStep.java:37)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.FlatMapStep.processNextStart(FlatMapStep.java:48)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.FlatMapStep.processNextStart(FlatMapStep.java:48)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.filter.FilterStep.processNextStart(FilterStep.java:37)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.FlatMapStep.processNextStart(FlatMapStep.java:48)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.MapStep.processNextStart(MapStep.java:36)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.SelectOneStep.processNextStart(SelectOneStep.java:131)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.next(AbstractStep.java:128)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.next(AbstractStep.java:38)
	at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversal.next(DefaultTraversal.java:205)
	at com.example.Queries.query(Queries.groovy:39)