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https://issues.apache.org/jira/browse/TINKERPOP-2510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17934197#comment-17934197
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Stephen Mallette commented on TINKERPOP-2510:
---------------------------------------------
Documented on 3.7-dev:
https://github.com/apache/tinkerpop/commit/6dda6f0df96aa852d20cac40c48144786645a6b5
> by-modulator throws when token is used after elementMap()
> ---------------------------------------------------------
>
> Key: TINKERPOP-2510
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2510
> Project: TinkerPop
> Issue Type: Bug
> Components: process
> Affects Versions: 3.4.9
> Reporter: Christopher Smith
> Priority: Major
>
> 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:
> {code:groovy}
> gts.V(entryPoint).as('p')
> .sideEffect(__.elementMap().group('pp').by(T.id))
> .out...
> ...
> .select('pp', ...)
> {code}
> 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.
> {code}
> 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)
> {code}
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