Create own context for mutation response resolvers

[mxstbr]

Imagine a mutation top edit a users username, which has a signature something like this:

type Mutation {
  changeUsername(username: String!): User
}

mutation changeUsername($username: String!) {
  changeUsername(username: $username {
    username
  }
}

In said mutation resolver, I now have to load the user for whatever reason. (in my real use case for checking permissions) I'm using DataLoader to do so to avoid repeated database calls:

const RootMutation = {
  changeUsername: (root, args, context) => {
    const user = context.loaders.user.load(args.input.id);
    // ...actual username changing code...
  }
}

In my query resolvers I also use the same loader to resolve a user object:

const RootQuery = {
  user: (root, args, context) => {
    return context.loaders.user.load(root.id || args.id)
  }
}

The issue I'm running into is that the query resolver for the single user returns the cached data from the dataloader without the new changes because the context is shared between the mutation resolver and the returned query resolvers:

this.props.changeUsername('new-username').then(result => {
  console.log(result) // { username: 'old-username' }
})

Now, in this specific case I can work around this by manually clearing the DataLoader cache with context.loaders.user.clear(id). I'm wondering though, maybe it'd make sense to create the context anew for the resolvers of a mutations return value vs. for the mutation resolver itself?

[leebyron]

Happy to entertain suggestions on how to do this, however I think the expectation is that since mutations definitionally are side-effectful on global state that doing things like clearing caches is totally within the expectations of the kind of work you would do in a mutation resolver

[Pruxis]

This is an issue I am running into aswell, I thought I was misreading the documentation when exploring this but it actuality seems to not be possible to update the context during a query / mutation.

[IvanGoncharov]

I thought I was misreading the documentation when exploring this but it actuality seems to not be possible to update the context during a query / mutation.

You can change things inside context but not a context itself.
Moreover, by putting DataLoader into the context you already mutating it every time you update its internal cache.
Nothing prevents you from fully replacing loaders property if you wish so.

In general, I think such issues should be solved by 3rd-party middlewares proposed in #1516

[IvanGoncharov]

After reading through #354, I think we need some way to modify the context for subsequent resolvers without affecting resolvers executed in parallel or next mutation.
But I don't think it should be mutation specific so we should focus on #354 instead