Question: variables get inlined... where? about bramble HOT 9 CLOSED

@gmac I had to track this one down myself but it's happening in formatSelectionSet here https://github.com/movio/bramble/blob/main/query_execution.go#L100 and that will trace down to expandAndFormatVariable. Essentially all of the variables are stored inside the http context and then inlined last minute based on matching up the variable names.

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@gmac variables are also used to evaluate @skip and @include directives here:

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Whhhoooaa, I totally overlooked the significance of the formatting lib here. I kind of assumed that was just a “dumb” string utility and that all the primary logic would be happening as an AST transformation in the execution process. Thanks for the pointer, I see it now!

One related question on @skip and @include… I was surprised to see those included in the gateway. Technically, couldn’t those just get passed through to the underlying subservices to evaluate? I guess that could mess with null evaluation?

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One related question on @Skip and @include… I was surprised to see those included in the gateway. Technically, couldn’t those just get passed through to the underlying subservices to evaluate? I guess that could mess with null evaluation?

It was relatively easy to implement so we added it in. I don't think there is a downside to doing this? With very large documents, it may also be quite a bit more efficient, since pruning the selection set may result in calling fewer downstream services.

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Makes sense. I can’t think of a downside either, I was just surprised to see them there.

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A year later I've probably found a downside of inlining. 🙂

I'm trying to implement patch-like update mutation and distinguish between null fields and not send (undefined).
So on service side I'm looking into variables (selection set) and skip any of them if they are not present.

Is it possible to pass variables to downstream services? Or maybe there is another workaround?

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@benzolium we also found an issue with inlining variables recently with custom scalars and the difference between serialisation as JSON and GraphQL.

I think the answer will be to stop expanding and inline variables into the downstream service queries, and instead extract the relevant variables from the request payload, and pass them downstream.

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@pkqk could you please guide me how can I do it? Should I make a fork of bramble?

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@benzolium if you'd like to have a go at it then you can fork bramble and make a PR to this repo.

In format.go it currently extracts the variables from the request context while formatting the queries for all the downstream services, and then inlines them into each query.

You'd need to alter buildBoundaryQueryDocuments and executeBoundaryQuery called in execution.go so instead it collects the variables used in each query and passes them along to the downstream services.

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