[v4] Implement documented polymorphic hierarchy support

[cdelacombaz]

Summary

The Payload v4 beta documentation describes support for polymorphic hierarchies using the relationTo property.

However, in 4.0.0-beta.6, the relationTo property does not exist on the HierarchyConfig type.

Documentation vs. implementation

Documentation:

• Polymorphic Hierarchies
• Hierarchy Config Options

The documentation includes the following example:

hierarchy: {
  parentFieldName: 'parent',
  relationTo: ['pages', 'posts'], // Posts can nest under pages OR other posts
}

Current implementation:

• HierarchyConfig type definition (GitHub)
• HierarchyConfig on the repository's default branch

The type definition does not include relationTo and describes hierarchies as self-referential, meaning documents can only nest under documents from the same collection.

Expected behavior

It should be possible to configure polymorphic hierarchies as documented, allowing documents from one collection to have parents from different collections.

Actual behavior

The relationTo property is missing from HierarchyConfig, so the documented configuration is not accepted by TypeScript.

Environment

• Payload version: 4.0.0-beta.6

Question

Is support for polymorphic hierarchies still planned for v4, or is this functionality expected to be available already?

If it is not implemented yet, it would be helpful to clarify its status in the beta documentation.

Thanks!