WooCommerce check if current product is being used in a Mix and Match parent product

wc_check_against_mix_match

global $wpdb;
$dmc_mnm_child_id = $product->get_id();
$querystr = "
    SELECT * 
    FROM $wpdb->postmeta
    WHERE $wpdb->postmeta.meta_key = '_mnm_data'
    AND $wpdb->postmeta.meta_value LIKE '%{$dmc_mnm_child_id}%'
";
 
$pageposts = $wpdb->get_results( $querystr, OBJECT );

// yes, it is
if( $pageposts != NULL ) {
// get mix n match parent product id
$dmc_mnm_parent_id = $pageposts[0]->post_id;
// get mix n match parent product permalink from the id
$dmc_mnm_parent_id = get_permalink( $dmc_mnm_parent_id );
// $dmc_mnm_parent_title = get_title( $dmc_mnm_parent_id );
// echo $dmc_mnm_parent_title;

// check referrering URL is from the mix n match parent product
if ( wp_get_referer() )
{
    $dmc_referrer = wp_get_referer();
    if ( strpos( $dmc_referrer, 'product' ) !== false) 
    // it is, so use the browser back button to maintain state
    { ?>
	<a href="<?php echo esc_url( $dmc_mnm_parent_id ); ?>" class="single_buy_in_case_button button alt" onclick="history.go(-1);"><?php echo _e( 'Back to Your Mixed Case' ); ?></a>
	<?php
    } else {
    // if not, use the default link back to the mix n match parent product ?>
	<a href="<?php echo esc_url( $dmc_mnm_parent_id ); ?>" class="single_buy_in_case_button button alt"><?php echo _e( 'Buy in a Mixed Case' ); ?></a>
   <?php
   }; // end check referrering URL 
}