---
url: /cookbook/modify-relation-data.md
description: >-
  Customize relation input data per REST request using the x-wpce-element-id and
  x-wpce-property-id headers.
---

# Modify Relation Data

Data of a [relation](/documentation/input-types/relation) JSON request can be modified using WordPress' built-in filters, namely `rest_{post_type}_query` and `rest_{taxonomy}_query`. To distinguish WPCE requests from other REST API requests, the editor sends along the `x-wpce-element-id` and `x-wpce-property-id` headers.

So for example to modify a relation input with the ID `posts` in an element with the ID `recent-posts` to only show posts by the current user, the following code could be used:

```php
add_filter('rest_post_query', function ($args, WP_REST_Request $request) {
	if (
		$request->get_header('x-wpce-element-id') === 'recent-posts' &&
		$request->get_header('x-wpce-property-id') === 'posts'
	) {
		$args['author'] = get_current_user_id();
	}

	return $args;
}, 10, 2);
```