How to forward generic types from custom baseQuery endpoints to query hooks

[david-mkl]

Using typescript 5.6 and rtk 2.2.

I am using createApi with a custom base query. Basically the issue is that the custom baseQuery calls an API that supports some complex type behavior. But this type information is lost when it is passed through createApi. I'm trying to find a way to preserve those types.

Here is a simplified snippet of what is going on

// Data returned from an API endpoint
type Data = {
  id: number;
  name: string;
  createdAt: string;
  updatedAt: string;
}
type DataFields<F extends keyof Data> = { [K in F]: Data[K] } & Partial<Omit<Data, F>>

class DataAPI {
  // the endpoint allows specifying the fields that are returned
  async getData<F extends keyof Data>(fields: F[]): Promise<DataFields<F>> {
    // ...
  }
}

// example usage of using the api directly
const data = await new DataAPI().getData(['id'])
// data is { id: number } and the other fields are marked as optional (for example, name?: string) since only "id" was passed as an argument

////////////////////////////////////////////////

// custom base query
const baseQuery = async (callAPI) => {
  try {
    const results = await callAPI(new DataAPI())
    return { data: results }
  } catch (error) {
    return { error }
  }
}

// create the api
const api = createApi({
  // ...
  baseQuery,
  endpoints: (builder) => ({
    // this is probably where the issue is.
    // no way to specify the generic fields param here
    getData: builder.query<Awaited<ReturnType<DataAPI["getData"]>>, Parameters<DataAPI["getData"]>[0]>({
      query: (fields) => (dataAPI) => dataAPI.getData(fields),
    }),
  }),
})

const { useGetDataQuery } = api

////////////////////////////////////////////////

// type information lost when calling the hook
const { data, error } = useGetDataQuery(['id'])
// data is { id: number; name: string; createdAt: string; updatedAt: string; } even though name, createAt, updatedAt are not set

As far as I can tell by reading through the types on query, there is no way to specify the generic type anywhere, so this is likely not supported. Any tips would be appreciated.

[markerikson]

I think the issue here is that TS can't carry generics like that through multiple levels, but @EskiMojo14 and @phryneas are probably able to answer that more definitively.

[EskiMojo14]

correct, TS has no way to carry generics like what would be required here.

[david-mkl]

Ah okay. Thanks for confirming that