Code-Snippets-Functions/Execute a function on a child site/WordPress/delete-all-but-the-oldest-revision.txt

add_filter(
        'wp_save_post_revision_revisions_before_deletion',
        function( $revisions, $post_id ) {
                $original_revision = get_transient( 'original_revision_for_post_' . $post_id );
                if ( $original_revision ) {
                        // Always remove the oldest revision from the array of revisions to potentially delete.
                        unset( $revisions[ $original_revision ] );
                } else {
                        // Set the oldest revision in a transient, so we can verify that it is always ignored.
                        $original_revision = array_key_first( $revisions );
                        set_transient( 'original_revision_for_post_' . $post_id, $original_revision );
                }
                return $revisions;
        },
        10,
        2
);