Mutation optional variables

I have a question about forcing None values inside mutation variables as null. Is this correct?

graphql_ppx/src/output_bucklescript_encoder.ml

Line 59 in 96ca3cb

    
           [%expr fun v -> match v with None -> Js.Json.null | Some v -> [%e child_parser] v] [@metaloc loc]

I think it will be more correct to treat None as undefined, and Some(Js.Nullable.null) as null inside make function.

itemInput = {
  id: Int, // <----- Optional
  name: String!
};
mutation createItem($input: itemInput!)

with CreateItem.make(~item={ "id": None, name: "foo" })" request payload will be {item: { id: null, name: "foo"}}.

if None will be treated as undefined - JSON.stringify will drop keys from request payload. I guess this can be tricky since Js.Json.t is used and undefined is not a JSON of course. We can filter them out then?

There is no way to replace Js.Json.null with undefined. According to glennsl/bs-json#50 (comment) solution would be to omit null value in field_array somewhere here

graphql_ppx/src/output_bucklescript_encoder.ml

Line 82 in 96ca3cb

[%expr Js.Json.object_ (Js.Dict.fromArray [%e field_array])] [@metaloc loc]

and remove all null values from the output JSON.

I understand how it should work but code generation is a little bit magical to me thus I have no idea how to implement it. Maybe @mhallin could help.

This sounds similar to #26, where the conclusion would be to use option(option(t)) for optional input variables. I'm thinking now that Js.Nullable would be a better solution, though. Either way, this is a breaking change.

+1 for Js.Nullable it also aligns well with Bucklescript 4.0.0 runtime representation for optionals.

None -> undefined
Some(null) -> null
Some("string") -> "string"