Unable to customise the Promise returned from a resolver

Context When using typestrict-resolvers plugin, and using the mappers property to map Prisma types

The problem I’m seeing is specific to union types. Prisma’s return types for findUnique is Promise<TModel | null> vs graphql-codegen expected type is Promise<TModel> | Promise<null>

This means that you can’t just return from a db.model.findUnique call in a resolver and the only viable solution is to do typecasting, because the Prisma type is more “strict” than the type generated by codegen.

The errors appear as follows (message will vary slightly depending on ResolverFn definition):

Type 'Promise<Post | null>' is not assignable to type 'Promise<null> | Promise<Post>'.

Describe the solution you’d like Either: a) The ability to customise how the Promise from a resolver is constructed OR b) Use unions inside the generic of the Promise i.e. ✅ Promise<TResult | null> ⚠️ and not Promise<TResult> | Promise<null>

Describe alternatives you’ve considered

• I tried changing the ResolverTypeWrapper - but to no effect

Additional context Follow this thread https://github.com/redwoodjs/redwood/issues/5481#issuecomment-1157814297 for a bit more info

[dac09]

Closing this issue - confirmed that you can use prisma findUniques!

Thanks so much @enisdenjo

[dac09]

Union members are indeed evaluated one by one, the following example proves the point:

Thanks a bunch @enisdenjo - this is really really great, and super happy to have a concrete explanation for this. ✌️

And appreciate the links to the handbook and your explanation- you have no idea how many people I’ve spoken to to try and get to the bottom of this!

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@n1ru4l It looks to me like we can probably close this issue - we still have to look into the other one in #8050 (the whole reaons this problem came up).