@oneOf Directive Support (help)

[maaft]

What happened?

@oneOf is a commonly used directive on input-types. graphql/graphql-spec#825

Using this directive, it is possible to validate that one (and only one) field from an input object is set, e.g:

input UserBy @oneOf {
  id: ID
  email: String
  username: String
  registrationNumber: Int
}

input UserInput {
  by: UserBy!
}

type Query {
  user(input: UserInput!): User
}

What did you expect?

It would be great, if gqlgen could support and validate this directive.

I already tried to implement it by myself, but I'm confused by the directive function syntax:

c.Directives.OneOf = func(ctx context.Context, obj interface{}, next graphql.Resolver) (res interface{}, err error) {

		return next(ctx)
	}

In theory, I need to iterate through all keys of obj and check if only one of them is !=nil.

Problems:

• This function seems to be called multiple times: First time for the UserInput type, then a 2nd time for the actual UserBy type on which the @oneOf directive is used.
• I'm only interested in the UserBy input type

Questions:

• How can I make sure to receive only UserBy types in my directive callback?
• The solution should be generic. I don't want to do type assertions (like _, ok := obj.(model.UserBy). The @oneOf directive will be used on multiple input times. I can't add a new type-assertion to the directive everytime a new input types uses that directive.

[maaft]

@frederikhors why move to discussion? This could be a bug IMHO

In my opinion, the directive callback should only be called with UserBy object, not with UserInput object first

[maaft]

I reworded it as an issue: #2281

[frederikhors]

Sorry to forgot a comment for you. You're right maybe it's a bug and I was wrong because I better understand it now in the reworded version #2281.