How do you use the sideEffect() method in the Gremlin npm package

Question

I've tried various ways of calling sideEffect(), but none have worked, I can't find any documentation or examples online, and the source code is a bit too abstract for me to understand without spending considerably longer looking at it.

As an example:

const y = await g.V().hasId('a4b64522-9cda-1b34-8f76-634242933a0d').sideEffect('drop()').next();

Results in

Error: Server error: {"requestId":"8915089a-cde3-4861-b73a-2534cefbc0b2","code":"InternalFailureException","detailedMessage":"Could not locate method: NeptuneGraphTraversal.sideEffect([drop()])"} (599)

I'm running these traversals against AWS Neptune in case that matters (although running similar queries through Python and the Gremlin Console against Neptune work).

Answer 1

The sideEffect() step takes an anonymous traversal so the syntax I provided in your previous question should work equally well in every Gremlin Language Variant including javascript:

g.V().hasId('a4b64522-9cda-1b34-8f76-634242933a0d').sideEffect(drop())

drop() is of course spawned from __ and should be part of your standard imports and can be called more explicitly as:

const __ = gremlin.process.statics;
g.V().hasId('a4b64522-9cda-1b34-8f76-634242933a0d').sideEffect(__.drop())

The error you describe in your question is simply related to your usage where you pass drop() as a string value. That said, I suppose it's possible that neptune doesn't support sideEffect() as a step at all?? You could test it with a more simple traversal with legitimate syntax and see if you get the same error:

g.V().hasId('a4b64522-9cda-1b34-8f76-634242933a0d').sideEffect(__.constant(1))

If that traversal returns a Vertex with the specified id you were querying for and you don't see an error then I would think sideEffect() as being a supported step. Perhaps someone with more Neptune experience will be able to offer a more official answer for you.