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https://issues.apache.org/jira/browse/TINKERPOP-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15125408#comment-15125408
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Marko A. Rodriguez commented on TINKERPOP-968:
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We had {{optional()}} in TinkerPop2. Its actually quite easy to implement. I'm
wondering why we don't have it in TinkerPop3 and I believe .... ?? ... that
[~dkuppitz] has an argument against it. ?
Note that if we do implement it for TinkerPop3, we might want to compile it as:
{code}
g.V().hasLabel('a').optional(out('ab')) ==>
g.V().hasLabel('a').union(identity(), out('ab'))
{code}
Is that the expected semantics -- sorta like {{emit().repeat()}}? The reason
for this is because we would want it to use global traversal in OLAP and well,
such {{branch/}} semantics are already implemented for us. Thoughts?
> Add first class support for an optional traversal
> -------------------------------------------------
>
> Key: TINKERPOP-968
> URL: https://issues.apache.org/jira/browse/TINKERPOP-968
> Project: TinkerPop
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.1.0-incubating
> Reporter: pieter martin
>
> Both SparQL and Cypher use the "Optional" keyword to indicate an optional
> traversal. SQL uses the "left join".
> Gremlin has no first class support for an optional traversal. It can be
> achieved with the choose step but it is verbose, unintuitive and not what the
> choose step is intended for.
> The benefits of optional traversals are many. In particular it makes it
> trivial to load complete subgraphs/trees with one easy to read intuitive
> gremlin statement.
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