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https://issues.apache.org/jira/browse/TINKERPOP-2710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17497006#comment-17497006
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Divij Vaidya edited comment on TINKERPOP-2710 at 2/23/22, 7:07 PM:
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> We've taken the posture lately that we want to generate less exceptions in
> Gremlin
The root cause of this error is absence of strongly defined type semantics in
Gremlin language. Any step can be placed after any other step in a traversal.
At runtime, the code does the validation and if step is used incorrectly we
throw an error, e.g.
{noformat}
gremlin> g.V().union(outE(),out()).in()
org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerEdge cannot be cast to
org.apache.tinkerpop.gremlin.structure.Vertex
Type ':help' or ':h' for help.
Display stack trace? [yN]{noformat}
Is there a difference between the syntax error for hasKey() posted in the Jira
and the query above?
was (Author: divijvaidya):
> We've taken the posture lately that we want to generate less exceptions in
> Gremlin
The root cause of this error is absence of strongly defined type semantics in
Gremlin language. Any step can be placed after any other step in a traversal.
At runtime, the code does the validation and if step is used incorrectly we
throw an error, e.g.
{noformat}
gremlin> g.V().union(outE(),out()).in()
org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerEdge cannot be cast to
org.apache.tinkerpop.gremlin.structure.Vertex
Type ':help' or ':h' for help.
Display stack trace? [yN]{noformat}
I might have missed the conversation so feel free to point me to it but this is
a case of
To clarify so that we are on the same page, by keeping the existing behaviour
we are saying that it is perfectly fine to have no-op syntax in Gremlin query
language.
> hasKey() should throw an error when invoked on Elements
> -------------------------------------------------------
>
> Key: TINKERPOP-2710
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2710
> Project: TinkerPop
> Issue Type: Bug
> Components: language, process
> Affects Versions: 3.6.0
> Reporter: Divij Vaidya
> Priority: Major
>
> *Context*
> hasKey() step can be added to the traversal when the traverser is of type
> Element or when it is of type Property.
> When step is invoked for traverser of type property, the behaviour is well
> defined as, "Remove the {{Property}} traverser if it does not match one of
> the provided keys." Example query:
> {noformat}
> gremlin> g.V().properties().hasKey('age').value()
> ==>29
> ==>27
> ==>32
> ==>35{noformat}
> When the step is invoked for traverser of type Element, the behaviour of the
> step is not documented. [Looking at the
> code|https://github.com/apache/tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/HasContainer.java#L59]
> implementation, it "removes the element traverser if element has a property
> with key as '~key' and the value of that property matches 'age'".
> But [this condition is
> unsatisfiable|https://github.com/apache/tinkerpop/blob/6a0b71b2af79b1b45f1e2db41946fe85529ed32e/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/util/ElementHelper.java#L84]
> because Element can never have a property with key "~key". It would always
> fail at insertion i.e. the output of hasKey() on Element traverser will
> always be empty.
> *Change proposed*
> Hence, I propose the following change:
> If hasKey() is applied to a traverser of Element type, then it should throw
> an error.
> The code change will be made
> [here|https://github.com/apache/tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/HasContainer.java#L59]
> . We would introduce a change as follows:
> {noformat}
> if (this.key.equals(T.key.getAccessor())) {
> throw new IllegalArgumentException("hasKey() cannot be applied to
> traverser of type Element")
> }{noformat}
> *Impact of the change*
> Before the change:
> {noformat}
> // the following query always returns empty results gremlin>
> g.V().hasKey('age').fold()
> gremlin> g.V().hasKey('age').fold()
> ==>[]{noformat}
>
> After the change:
> {noformat}
> // the following query returns an error
> gremlin> g.V().hasKey('age').fold()
> hasKey() cannot be applied to traverser of type Element{noformat}
>
>
>
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