Relay: Enhancement of the customScalars format for typescript

[pebeka]

As of today, the customScalars format is straightforward, just a string / string mapping, and then limit the use of custom scalars to native types.
The customScalars format can be enhanced to support more complex types:
A proposal can be:

const customScalars = {
  MyType: {
    type: 'MyType',
    module: '../myModule'
  },
  MySimpleString: 'String'  
}

this will add

import { MyType } from '../myModule';

in the generated file.
Do you agree with that format?
I can do a PR on the relay-tools/relay-compiler-language-typescript repo.

[alloy]

(When I suggested opening this ticket, I meant it to be agnostic of programming language. The TS plugin simply follows what Relay does.)

[pebeka]

ok, the typing language agnostic view of the proposal:
customScalars is an object with keys as custom type name, and their associated value is either a string or an object with a 'type' key and eventually other keys:

const customScalars = {
  MyType: {
    type: 'MyType',
    // other props specific to a typing language
    module: '../myModule',
  },
  MySimpleString: 'String',
  // or the equivalent declaration:   
  MySimpleString: {
    type: 'String',
  }   
}

[itajaja]

this would be really great. To add to @pebeka proposal, to make it truly agnostic, I think it's necessary to provide a map for each target language. something like:

customScalars: {
  MyType: {
    flow: X,
    typeScript: Y,
  }
}

how X and Y look is actually specified by the plugin itself and relay-compiler remains unopinionated (for example, one implementation could be @pebeka's proposal, another could be a simple string that is evaled, etc).

[taion]

It'd be sort of weird for types to have different names in Flow and TS, esp. if any of them are runtime types, no?

[itajaja]

not different names, different definitions, eg typescript's Record is different from whatever flow has

[mattkrick]

a proposal for the proposal: allow a custom scalar to have a serialized & a parsed value.

For example, a custom DateTime will come back as a string in the response payload. However, if I use DateTime as an argument, I'd like it to be a Date. Apologies if this is already possible, just haven't figured out how to do it yet!

[Eldow]

I'm using io-ts right now to serialize and deserialize at runtime the iso-strings received from my DB to Moment objects.

export const DateTime = new t.Type<moment.Moment, string>(
  'DateTime',
  (mixed): mixed is moment.Moment => moment.isMoment(mixed),
  (mixed, context) =>
    pipe(
      t.string.validate(mixed, context),
      either.chain(str => {
        const instance = moment(str)
        return instance.isValid() ? t.success(instance) : t.failure(str, context)
      })
    ),
  instance => instance.toISOString()
)

For now, I just map the payloads and responses to fit my needs but having custom scalars would be so much more convenient.

I would really like to have the ability to automatically decode payloads and encode responses when they are flagged with a specific GraphQL scalar by providing the appropriate handler to Relay Compiler.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.