functions.php

/**
 * Add a Gravity forms form to product upon database save.
 *
 * Requires Gravity Forms and WooCommerce - Gravity Forms Product Add-Ons.
 *
 * Search for '_gravity_form_data' in wp_postmeta and set $raw_form_data to the serialized string. 
 *
 * @return void
 **/
function mb_woo_product_insert_form($product_ID) {
     $raw_form_data = ''; // Add serialized form data from MySQL here
     $form_data = unserialize($raw_form_data);
     $meta_key = '_gravity_form_data';

     $existing_meta = get_post_meta($product_ID, $meta_key, $single = true);
     if ( strlen($existing_meta) > 0 ) return;
     update_post_meta($product_ID, $meta_key, $form_data);
}

add_filter('save_post', 'mb_woo_product_insert_form');