public function update_product_sales( $product_id, $quantity = null, $operation = 'set' ) {
		global $wpdb;
		add_post_meta( $product_id, 'total_sales', 0, true );

		// Update stock in DB directly.
		switch ( $operation ) {
			case 'increase':
				// phpcs:ignore WordPress.VIP.DirectDatabaseQuery.DirectQuery
				$wpdb->query(
					$wpdb->prepare(
						"UPDATE {$wpdb->postmeta} SET meta_value = meta_value + %f WHERE post_id = %d AND meta_key='total_sales'",
						$quantity,
						$product_id
					)
				);
				break;
			case 'decrease':
				// phpcs:ignore WordPress.VIP.DirectDatabaseQuery.DirectQuery
				$wpdb->query(
					$wpdb->prepare(
						"UPDATE {$wpdb->postmeta} SET meta_value = meta_value - %f WHERE post_id = %d AND meta_key='total_sales'",
						$quantity,
						$product_id
					)
				);
				break;
			default:
				// phpcs:ignore WordPress.VIP.DirectDatabaseQuery.DirectQuery
				$wpdb->query(
					$wpdb->prepare(
						"UPDATE {$wpdb->postmeta} SET meta_value = %f WHERE post_id = %d AND meta_key='total_sales'",
						$quantity,
						$product_id
					)
				);
				break;
		}

		wp_cache_delete( $product_id, 'post_meta' );

		$this->update_lookup_table( $product_id, 'wc_product_meta_lookup' );

		/**
		 * Fire an action for this direct update so it can be detected by other code.
		 *
		 * @since 3.6
		 * @param int $product_id Product ID that was updated directly.
		 */
		do_action( 'woocommerce_updated_product_sales', $product_id );
	}