Relationship Sync for ACF

Link any two Advanced Custom Fields relationship fields from a settings page and keep them in sync bidirectionally. Editing either side updates the other automatically — no code required.

Unlike same-field-name approaches (and ACF's own built-in bidirectional option, which works on a single field), this plugin lets you map two different fields across different post types from an admin UI, and also supports symmetric (mutual) relationships.

Features

• Settings page (Settings → Relationship Sync) to link any two ACF relationship fields.
• Automatic two-way sync on save — add/remove a relationship on one side, the other updates itself.
• Cross-field / cross-post-type mappings; fields don't need the same name.
• Symmetric mappings — pick the same field on both sides for a mutual relationship (A→B implies B→A).
• Per-mapping backfill to align pre-existing data in one click.
• Enable/disable mappings without deleting them.
• Writes the ACF field-key reference so synced values render correctly in the editor.

Requirements

• WordPress 5.8+, PHP 7.4+
• Advanced Custom Fields (free or Pro)
• Works on top-level relationship fields (not fields nested inside Repeater / Flexible Content — their meta keys are dynamic).

Installation

1. Copy this repository's plugin files into wp-content/plugins/relationship-sync-for-acf/ (the main file, relationship-sync-for-acf.php, plus includes/), or build a zip of those files and upload via Plugins → Add New → Upload Plugin.
2. Activate it.
3. Go to Settings → Relationship Sync, add a mapping, and run Backfill once if you have existing data to align.

How it works

On acf/save_post, the engine runs every enabled mapping the saved post is part of. For each mapping it:

1. Reads the post types each field applies to (from the field's ACF field group location rules).
2. Reconciles the opposite field across those posts — adding the link where the source now points, removing it where it no longer does.

A recursion guard plus direct update_post_meta writes (which don't re-trigger acf/save_post) keep it from looping. Self-mapped fields use a symmetric reconcile.

Repository layout

relationship-sync-for-acf.php   # main plugin file (v2.1.0)
includes/
  class-rsfa-sync.php           # sync engine
  class-rsfa-admin.php          # settings page
uninstall.php                   # option cleanup on delete
languages/                      # translation template (.pot)
readme.txt                      # wordpress.org readme
history/                        # prior versions, preserved for reference
  1.1.0/  1.2.0/  2.0.0/

The history/ folder archives the plugin's evolution from the original site-specific build (NEC Relationship Sync) to the generic, configurable release.

wordpress.org submission readiness

• Text domains are passed as string literals in every translation call (i18n-scanner compatible).
• Translation template included at languages/relationship-sync-for-acf.pot; load_plugin_textdomain() is wired up on boot.
• uninstall.php removes the rsfa_mappings / rsfa_migrated options (and legacy keys) on delete; synced relationship values are left intact as real post data.

Remaining nice-to-haves: add screenshots to the readme, and run the official Plugin Check (PCP) plugin before submitting.

License

GPL-2.0-or-later. See LICENSE.