[Docs]: Missing documentation on relation resolvers in a service

[dac09]

Summary and description

We don't really talk about how the relation resolvers generated at the bottom of a service file work.

The only mention is here: https://redwoodjs.com/docs/graphql#redwoods-resolver-args - which is useful, but not enough IMO.

What do I mean by relation resolvers?

// services/posts.ts

export const post: QueryResolvers['post'] = /**/
export const createPost: MutationResolvers['createPost'] =  /**/

// 👇 these are your "relation" or field resolvers
- export const Post: PostResolvers = {
+ export const Post: PostRelationResolvers = {
  author: (_obj, gqlArgs) => /**/
}

These resolvers are invoked when a "relation" on the Post model is invoked, in this case if the query requested Post.author.name for example.

Things we should cover:

• how does a query/mutation map to a service function?
• what is the order of preference i.e. if you define a relation resolver for a field, it will be invoked first
• how to optimise queries either:
  a) use prisma includes in the main service function + check if already included in root)
  b) use dataloaders

Are you interested in working on this?

• I'm interested in working on this

[cannikin]

I've started on this in the tutorial here: #6465

[dac09]

@cannikin is it worth adding a section the docs/reference (in the services section) and not just the tutorial?

It honestly is one of the most confusing things in services - happy to give it a go if you want to focus on the tutorial piece.

[cannikin]

Yep, I had planned to add a more in-depth section in the Services docs themselves. Feel free to add something if you need a break from Typescript for a while! :)

[cannikin]

This probably shouldn't be closed—this was referring to a more in-depth description of relation resolvers, while the intro in the tutorial is pretty minor.

[cannikin]

I assigned this over to you @dac09 but let me know if you change your mind!