ts-client custom scalars

[jasonkuhrt]

Perceived Problem

Custom scalars have no runtime codec.

Ideas / Proposed Solution(s)

Allow the generator to have custom scalar codecs specified. Maintain a runtime schema type map. Pass requests/responses through a middleware that uses the runtime schema type map to apply encoders/decoders to custom scalar fields.

Codecs

gr --codecs './customScalarCodecs.ts'

By default look for a a file at <outputDirPath>/customScalarCodecs.ts or <outputDirPath>/custom-scalar-codecs.ts.

The contract for the module is exported codecs whose names match a custom scalar in the schema.

Example:

import { createCodec } from 'graphql-request/alpha/scalars'


export const Date = createCodec({
  encode: (date) => date.getTime(),
  decode: (number) => new Date(number)
})

When a custom scalar has no defined codec then an error is thrown.

** Automatic Runtime codec application **

Use a type map that knows which parts of the schema are custom scalars. This runtime type map will be part of the code generation.

Example type map:

import * as CustomScalarCodecs from '...'

export const CustomScalarSchema = {
  query: {
    date: CustomScalarCodecs.Date
  }
}

An internal middleware will be used doing something like as follows.

const processCustomScalars = (grDocument) => {
  const encodedGrDocument = encode(typeMap, grDocument)
  const result = await send(typeMap, encodedGrDocument)
  const decodedResult = decode(result)
}

const encode = (typeMap, grDocument) => {
  return Object.fromEntries(Object.entries(grDocument).map(([key,value]) => {
    if (typeMap[key]) {
      if (typeMap[key].kind === 'Scalar') {
        return [key, typeMap[key].codec.encode(value)]
      } else {
        return [key, return encode(typeMap[key], value[key])]
      }
    } else {
     return [key, value]
    }
  }))
}

const decode = (typeMap, result) => {
  return Object.fromEntries(Object.entries(result).map(([key,value]) => {
    if (typeMap[key]) {
      if (typeMap[key].kind === 'Scalar') {
        return [key, typeMap[key].codec.decode(value)]
      } else {
        return [key, return decode(typeMap[key], value[key])]
      }
    } else {
     return [key, value]
    }
  }))
}