Mercator\Mapping::get_by_domain PHP Method

    public static function get_by_domain($domains)
    {
        global $wpdb;
        $domains = (array) $domains;
        // Check cache first
        $not_exists = 0;
        foreach ($domains as $domain) {
            $data = wp_cache_get('domain:' . $domain, 'domain_mapping');
            if (!empty($data) && $data !== 'notexists') {
                return new static($data);
            } elseif ($data === 'notexists') {
                $not_exists++;
            }
        }
        if ($not_exists === count($domains)) {
            // Every domain we checked was found in the cache, but doesn't exist
            // so skip the query
            return null;
        }
        $placeholders = array_fill(0, count($domains), '%s');
        $placeholders_in = implode(',', $placeholders);
        // Prepare the query
        $query = "SELECT * FROM {$wpdb->dmtable} WHERE domain IN ({$placeholders_in}) ORDER BY CHAR_LENGTH(domain) DESC LIMIT 1";
        $query = $wpdb->prepare($query, $domains);
        // Suppress errors in case the table doesn't exist
        $suppress = $wpdb->suppress_errors();
        $mapping = $wpdb->get_row($query);
        $wpdb->suppress_errors($suppress);
        if (empty($mapping)) {
            // Cache that it doesn't exist
            foreach ($domains as $domain) {
                wp_cache_set('domain:' . $domain, 'notexists', 'domain_mapping');
            }
            return null;
        }
        wp_cache_set('domain:' . $mapping->domain, $mapping, 'domain_mapping');
        return new static($mapping);
    }

/**
 * Register filters for URLs, if we've mapped
 */
function register_mapped_filters()
{
    $current_site = $GLOBALS['current_blog'];
    $real_domain = $current_site->domain;
    $domain = $_SERVER['HTTP_HOST'];
    if ($domain === $real_domain) {
        // Domain hasn't been mapped
        return;
    }
    // Grab both WWW and no-WWW
    if (strpos($domain, 'www.') === 0) {
        $www = $domain;
        $nowww = substr($domain, 4);
    } else {
        $nowww = $domain;
        $www = 'www.' . $domain;
    }
    $mapping = Mapping::get_by_domain(array($www, $nowww));
    if (empty($mapping) || is_wp_error($mapping)) {
        return;
    }
    $GLOBALS['mercator_current_mapping'] = $mapping;
    add_filter('site_url', __NAMESPACE__ . '\\mangle_url', -10, 4);
    add_filter('home_url', __NAMESPACE__ . '\\mangle_url', -10, 4);
    // If on network site, also filter network urls
    if (is_main_site()) {
        add_filter('network_site_url', __NAMESPACE__ . '\\mangle_url', -10, 3);
        add_filter('network_home_url', __NAMESPACE__ . '\\mangle_url', -10, 3);
    }
}