public function get_sortable_columns() {
		return [
			'order'            => 'order_id',
			'purchaser'        => 'purchaser_full_name',
			'email'            => 'purchaser_email',
			'date'             => 'purchase_time',
			'gateway'          => 'gateway',
			'gateway_order_id' => 'gateway_id',
			'status'           => 'status',
			'total'            => 'total_value'
		];
	}