Part of the @oneOf directive initiative tracked in #3050 (this is Phase 3: Mutation Inputs).

Goal

Use @oneOf input types to enable polymorphic mutations, which are clunky or impossible today without oneOf.

Polymorphic content creation

A single, extensible creation mutation instead of one per post type:

input CreateContentNodeInput @oneOf {
  post: CreatePostInput
  page: CreatePageInput
  mediaItem: CreateMediaItemInput
  # extensible for custom post types
}

extend type RootMutation {
  createContentNode(input: CreateContentNodeInput!): CreateContentNodePayload!
}

@oneOf guarantees exactly one content type is supplied, and the payload returns the polymorphic node for inline-fragment selection.

Relationship management

input PostCategoriesInput @oneOf {
  set: [CategoryInput]      # replace all
  add: [CategoryInput]      # append
  remove: [CategoryInput]   # remove specific
  clear: Boolean            # remove all
}

Scope / constraints

• Additive. New mutations land alongside the existing createPost/createPage/etc.; nothing is removed here. Any eventual consolidation is a separate, later major decision.
• Per-field deprecation only. This does NOT depend on a generic legacy-argument-transformation layer (that approach was de-scoped, see Introduce support for the @oneOf GraphQL Directive #3050).
• Establishes the polymorphic-mutation pattern that Phase 4 (block editor / ACF flexible-content mutations) builds on, tracked via 🔬 Spike: mapping Gutenberg Blocks to the WPGraphQL Schema #3950 and the ACF plugin.

Related

• Introduce support for the @oneOf GraphQL Directive #3050 — @oneOf initiative (epic / tracker)
• Implement oneOf "by" arguments to replace id and idType pattern. #3416 — Phase 1 (singular by args)
• Implement consistent filter arg across connections #1385 — Phase 2 (connection filter/sort; oneOf is one mechanism within that RFC)
• 🔬 Spike: mapping Gutenberg Blocks to the WPGraphQL Schema #3950 — Phase 4 (Gutenberg blocks → schema, polymorphic block mutations)