WordPress: Copy related post IDs from Microkids's Related Posts data to and ACF Relationship field (named: 'related_posts').

wp-mrp-to-acf-related-posts.php

<?php
// IN TEST MODE. UNCOMMENT update_field() BELOW TO RUN.
/* Get posts sorted by ID */
$args_posts = array(
    'post_type'      => array( 'post', 'page' ), // Or 'any'.
    'fields'         => 'ids',
    'posts_per_page' => -1,
    'orderby'        => 'ID',
    'order'          => 'ASC',
);
$query_posts = new WP_Query( $args_posts );

/* Copy MRP array of IDs into ACF field, check for success and log */
if ( $query_posts->have_posts() ) {
    echo '<table class="tabular" style="width: 50%;">';
    while ( $query_posts->have_posts() ) {
        $query_posts->the_post();
        $post_id   = get_the_ID();
        $post_type = get_post_type();

        if ( MRP_get_related_posts( $post_id ) ) {
            // Get array of MRP IDs.
            $post_rel_mrp_arr = array_keys( MRP_get_related_posts( $post_id ) );
            // Copy MPR IDs into ACF field, returns post_meta ID.
            $update_field = '--';
            // UNCOMMENT To RUN:
            // $update_field = update_field( 'related_posts', $post_rel_mrp_arr, $post_id );

            // Log post meta data into HTML table, with check for success.
            $post_rel_mrp_ids = ( is_array( $post_rel_mrp_arr ) ) ? implode( ',', $post_rel_mrp_arr ) : '--';
            $post_rel_acf_arr = get_post_meta( $post_id, 'related_posts' );
            $post_rel_acf_ids = ( is_array( $post_rel_acf_arr[0] ) ) ? implode( ',', $post_rel_acf_arr[0] ) : '--';
            // Test for matched IDs in MRP and ACF fields.
            $copy_ids_check   = ( $post_rel_mrp_ids === $post_rel_acf_ids ) ? 1 : 0;
        ?>
        <tr><td><?php echo $post_type; ?></td><td><a href="/?p=<?php echo $post_id; ?>"><?php echo $post_id; ?></a></td><td><?php echo count( $post_rel_mrp_arr ); ?></td><td><?php echo $post_rel_mrp_ids; ?></td><td><?php echo $post_rel_acf_ids; ?></td><td><?php echo $copy_ids_check; ?></td><td><?php echo $update_field; ?></td></tr>
        <?php
        } else { // No MRP IDs.
        ?>
        <tr><td><?php echo $post_type; ?></td><td><a href="/?p=<?php echo $post_id; ?>"><?php echo $post_id; ?></a></td><td>0</td><td></td><td></td><td></td><td></td></tr>
        <?php
        }
    }
    echo '</table>';
} else {
    echo 'No posts found.';
}

wp_reset_postdata();

/*

MRP IDs
print_r( array_keys( MRP_get_related_posts( $post_id ) ) );
Array
        (
    [0] => 7108
    [1] => 9251
    [2] => 10546
    [3] => 10797
)

Copied to ACF field:
print_r( get_post_meta( $post_id , 'related_posts' ) );
Array
(
    [0] => Array
        (
            [0] => 7108
            [1] => 9251
            [2] => 10546
            [3] => 10797
        )

)

Serialized:
print_r( get_post_custom( $post_id ] ) );
    [related_posts] => Array
        (
            [0] => a:4:{i:0;s:4:"1234";i:1;s:4:"5678";i:2;s:5:"12345";i:3;s:5:"67890";}
        )

*/
?>