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https://issues.apache.org/jira/browse/TINKERPOP-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15136418#comment-15136418
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pieter martin commented on TINKERPOP-968:
-----------------------------------------
Turns out for the example above the {{optional}} (that I envisage) as
{{coalesce(traversal, identity)}} is not equivalent.
{code}
g.V().hasLabel('A').coalesce(out('ab'),identity()).coalesce(out('bc'),identity()).path()
{code}
returns
{code}
[v[0], v[4], v[8]]
[v[0], v[6], v[6]]
[v[2], v[2], v[2]]
{code}
Instead I am expecting,
{code}
[v[0], v[4], v[8]]
[v[0], v[6]]
[v[2]]
{code}
The identity() being passed along is not behaving optionally but rather
coalescy.
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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