Paid Memberships Pro - Add Discount Code to MailChimp Export

pmpro-add-discount-code-mailchimp-export.php

<?php
/**
 * This recipe merges any discount codes that a user has used to the MailChimp export.
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_mailchimp_listsubscribe_fields( $fields, $user ) {
	global $wpdb;
	$new_fields = array(
		'DISCOUNT_CODE_ID' => '',
		'DISCOUNT_CODE'    => '',
	);
	$code_id_sql = "SELECT code_id FROM {$wpdb->pmpro_discount_codes_uses} WHERE user_id = %d LIMIT 1";
	$new_fields = array();
	$code_id = $wpdb->get_var( $wpdb->prepare( $code_id_sql, $user->ID ) );
	if ( $code_id ) {
		$discount_code_sql = "SELECT code FROM {$wpdb->pmpro_discount_codes} WHERE id = %d LIMIT 1";
		$discount_code = $wpdb->get_var( $wpdb->prepare( $discount_code_sql, $code_id ) );
		if ( $discount_code ) {
			$new_fields = array(
				'DISCOUNT_CODE_ID' => absint( $code_id ),
				'DISCOUNT_CODE'    => sanitize_text_field( $discount_code ),
			);
		}
	}

	if ( ! empty( $new_fields ) ) {
		$fields = array_merge( $fields, $new_fields );
	}
	return $fields;
}
add_filter( 'pmpro_mailchimp_listsubscribe_fields', 'my_pmpro_mailchimp_listsubscribe_fields', 10, 2 );