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https://issues.apache.org/jira/browse/TINKERPOP-1506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15622906#comment-15622906
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ASF GitHub Bot commented on TINKERPOP-1506:
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GitHub user okram opened a pull request:
https://github.com/apache/tinkerpop/pull/471
TINKERPOP-1506: Optional/Coalesce should not allow sideEffect traversals.
https://issues.apache.org/jira/browse/TINKERPOP-1506
`g.V(1).optional(addV())` created 2 vertices, not one. This is because
`optional()` was implemented with the branch-step `ChooseStep`. This has been
fixed with a custom `OptionalStep`. Test cases added to verify correct behavior.
Added to `master/` as this is a breaking change. Though, the previous
behavior can easily be deemed a bug.
VOTE +1.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/apache/tinkerpop TINKERPOP-1506
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/tinkerpop/pull/471.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #471
----
commit 40971c95903077d38cb754843eb914b5548f5c1f
Author: Marko A. Rodriguez <[email protected]>
Date: 2016-10-31T18:03:33Z
added OptionalStep to be used instead of optional() being backed by
ChooseStep. This fixes a side-effect issue.
----
> Optional/Coalesce should not allow sideEffect traversals.
> ---------------------------------------------------------
>
> Key: TINKERPOP-1506
> URL: https://issues.apache.org/jira/browse/TINKERPOP-1506
> Project: TinkerPop
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.1.4, 3.2.2
> Reporter: Marko A. Rodriguez
>
> It took me a long time to realize what was wrong with a traversal I wrote
> that used {{optional(blah.sideEffect.blah)}}. {{optional()}} maps to
> {{ChooseStep}} under the hood and the provide traversal is first tested for a
> {{hasNext()}}. If so, the it plays itself out. The problem is that if there
> is a side-effect in the traversal child, then it gets executed twice.
> {code}
> gremlin> g = TinkerGraph.open().traversal()
> ==>graphtraversalsource[tinkergraph[vertices:0 edges:0], standard]
> gremlin> g.inject(1).optional(addV('twin'))
> ==>v[1]
> gremlin> g.V().valueMap(true)
> ==>[id:0,label:twin]
> ==>[id:1,label:twin]
> {code}
> We should NOT allow {{optional()}} to have {{SideEffectStep}} steps in it so
> as not to cause unexpected behavior. {{StandardVerificationStrategy}} can
> analyze and throw an exception if necessary.
> Also, {{coalesce()}} has a similar problem, though perhaps it can be a useful
> 'technique.'
> {code}
> gremlin> g = TinkerGraph.open().traversal()
> ==>graphtraversalsource[tinkergraph[vertices:0 edges:0], standard]
> gremlin> g.inject(1).coalesce(addV('twin1').limit(0), addV('twin2'))
> ==>v[1]
> gremlin> g.V().valueMap(true)
> ==>[id:0,label:twin1]
> ==>[id:1,label:twin2]
> gremlin>
> {code}
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