Relationship Types

Relationship types define the kind of link between two objects (e.g. "related to", "parent of").

Built-in types (post–post)

Type	Direction	Typical use
related_to	Bidirectional	Related posts, related products
parent_of	Unidirectional	Parent–child (e.g. course → lessons)
references	Unidirectional	Citations, references
depends_on	Unidirectional	Dependencies

Built-in types (user–post)

Type	Direction	Typical use
favorite_posts	User → post	User’s favorite posts
bookmarked_by	User → post	User bookmarks (same storage, different label)
authored_by	Post → user	Multiple authors / contributors

Built-in types (post–term)

Type	Direction	Typical use
categorized_as	Post → term	Featured categories, curated collections

Object types

Each relation has a from (source) and to (target). Each side is one of:

• post — Any post type (post, page, product, etc.)
• user — WordPress user
• term — Taxonomy term

A relationship type declares which from/to combinations are allowed (e.g. post → post, post → user).

Constraints

Types can define:

• max_connections — e.g. at most one "author" per post
• direction — from_to, to_from, or bidirectional (see Direction)

Custom types

Register custom types with ncr_register_relation_type(). See Custom types.