Martin Häusler created TINKERPOP-2873:
-----------------------------------------
Summary: Allow Union of Traversals
Key: TINKERPOP-2873
URL: https://issues.apache.org/jira/browse/TINKERPOP-2873
Project: TinkerPop
Issue Type: New Feature
Components: language
Affects Versions: 3.6.2
Reporter: Martin Häusler
Currently, it is possible to use the gremlin "union(...)" step as a union based
on *traversers*. The union takes each incoming traverser, and clones it for
each sub-traversal and feeds it to the sub-traversal as input.
There is another type of union, which relates more to a SQL "UNION ALL"
command. This second type of union is the union of *Traversals*. So we have
*independent* traversals with their own start and end steps, and we want to
combine them into a single traversal. The outcome of this traversal is the
union of the outcome of all sub-traversals.
One way to achieve this would be to allow "union(...)" step as the initial step
for a traversal:
{code:java}
g.traversal().union(t1, t2, t3) ... // traversal continues here
{code}
The purpose of this mechanism is:
* The root traversal after the "union(...)" step has access to all of the
labels and side effect keys of the sub-traversals and can operate on them.
* The root traversal can operate on the resulting traversers and continue to
filter them, perform navigation steps, etc.
Currently, the workaround for this kind of "traversal union" is:
{code:java}
g.traversal().inject(0).union(t1, t2, t3) ... // traversal continues here
{code}
Here, we inject a dummy value of 0 into the traversal which only exists to
trigger the union step, where it is discarded immediately by all alternatives
(which come with their own start steps). This works as intended and also shares
side effect keys etc. but is syntactically unpleasant and rather confusing to
read.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
