Alert: This function’s access is marked private. This means it is not intended for use by plugin or theme developers, only in other core functions. It is listed here for completeness.

_wp_preview_post_thumbnail_filter( null|array|string $value, int $post_id, string $meta_key )

Filters post thumbnail lookup to set the post thumbnail.

Parameters Parameters


(null|array|string) (Required) The value to return

  • a single metadata value, or an array of values.


(int) (Required) Post ID.


(string) (Required) Meta key.

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Return Return

(null|array) The default return value or the post thumbnail meta array.

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Source Source

File: wp-includes/revision.php

function _wp_preview_post_thumbnail_filter( $value, $post_id, $meta_key ) {
	$post = get_post();
	if ( ! $post ) {
		return $value;

	if ( empty( $_REQUEST['_thumbnail_id'] ) ||
		empty( $_REQUEST['preview_id'] ) ||
		$post->ID != $post_id ||
		'_thumbnail_id' !== $meta_key ||
		'revision' === $post->post_type ||
		$post_id != $_REQUEST['preview_id'] ) {

		return $value;

	$thumbnail_id = (int) $_REQUEST['_thumbnail_id'];
	if ( $thumbnail_id <= 0 ) {
		return '';

	return (string) $thumbnail_id;

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Changelog Changelog

Version Description
4.6.0 Introduced.

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