protected function save_items() {
		$items_changed = false;

		foreach ( $this->items_to_delete as $item ) {
			$item->delete();
			$items_changed = true;
		}
		$this->items_to_delete = array();

		// Add/save items.
		foreach ( $this->items as $item_group => $items ) {
			if ( is_array( $items ) ) {
				$items = array_filter( $items );
				foreach ( $items as $item_key => $item ) {
					$item->set_order_id( $this->get_id() );

					$item_id = $item->save();

					// If ID changed (new item saved to DB)...
					if ( $item_id !== $item_key ) {
						$this->items[ $item_group ][ $item_id ] = $item;

						unset( $this->items[ $item_group ][ $item_key ] );

						$items_changed = true;
					}
				}
			}
		}

		if ( $items_changed ) {
			delete_transient( 'wc_order_' . $this->get_id() . '_needs_processing' );
		}
	}