[GitHub] [tinkerpop] spmallette commented on a change in pull request #1555: TINKERPOP-2681 mergeE() and mergeV()

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spmallette commented on a change in pull request #1555:
URL: https://github.com/apache/tinkerpop/pull/1555#discussion_r797529098



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File path: docs/src/upgrade/release-3.6.x.asciidoc
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@@ -29,6 +29,71 @@ Please see the link:https://github.com/apache/tinkerpop/blob/3.6.0/CHANGELOG.asc
 
 === Upgrading for Users
 
+==== mergeV() and mergeE()
+
+One of the most commonly used patterns in Gremlin is the use of `fold().coalesce(unfold(), ...)` to perform upsert-like
+functionality. While this pattern is quite flexible, it can also be confusing to new users and for certain use cases
+challenging to get the pattern correctly implemented. For providers, the pattern is difficult to properly optimize
+because it can branch into complexity quite quickly making it hard to identify a section of Gremlin for an upsert and
+therefore is not executed as efficiently as it might have been otherwise.
+
+The new `mergeV()` and `mergeE()` steps greatly simplify this pattern and as the pattern is condensed into a single
+step it should be straightforward for providers to optimize as part of their implementations. The following example
+demonstrates just how much easier implementing a basic upsert of a vertex has gotten:
+
+[source,text]
+----
+// prior to 3.6.0, use fold().coalesce(unfold(), ...)
+gremlin> g.V().has('person','name','vadas').has('age', 27).
+......1>   fold().
+......2>   coalesce(unfold().property('age',30),
+......3>            addV('person').property('name','vadas').property('age',27)).

Review comment:
       > I find the example here already quite advanced and not obvious to understand.
   
   well, i think that's somewhat indicative of why these steps needed to be added. i tried to pick an easy one already....you should see a "hard" one. 😄  that said, i've added a more simple example along the lines you described.




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