Support 'OneOf Input Objects' from new GraphQL Spec(September 2025 Edition)

[toy0605]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

Description

The September 2025 Edition of the GraphQL Specification has been released,
and a new feature(OneOf Input Objects) has been officially introduced.

However, it requires discussion on how this should be implemented and exposed for usage.

Adapter support status

• ✅ Apollo Server is supported, but I couldn't find related documentation
• ❓ I couldn’t find any reference for Mercurius

Describe the solution you'd like

This is just a suggestion and should be open for discussion.

Suggestion example

// New `isOneOf` property
@InputType({ isOneOf: true })
export class UserByInput {
  @Field(type => ID)
  id: string;

  @Field(type => String)
  email: string;

  @Field(type => String)
  username: string;
}

@Resolver(of => User)
export class UserResolver {
  @Query(type => User)
  user(@Args("by") by: UserByInput) {
    // ...
  }
}

input UserByInput @oneOf {
  id: ID
  email: String
  username: String
}

type Query {
  user(by: UserByInput!): User
}

Teachability, documentation, adoption, migration strategy

No response

What is the motivation / use case for changing the behavior?

New GraphQL Specification

• September 2025 Edition of the GraphQL Specification
• Announcing the September 2025 Edition of the GraphQL Specification
• Safer Multi-option Inputs with @oneOf
• GraphQL Spec RFC #825
• graphql-js OneOf input objects Documentation

[toy0605]

I'll write PR for this feature.

[kamilmysliwiec]

Let's track this here feat(graphql): support one of input objects #3688