checkin: ensure that users are checked out first

			return ( undef, "Train ${train_id} not found" );

		}

		else {

			my $user = $self->get_user_status;

			if ( $user->{checked_in} ) {

              # If a user is already checked in, we assume that they forgot to

              # check out and do it for them.

              # XXX this is an ugly workaround for the UNIQUE constraint on

              # (user id, action timestamp): Ensure that checkout and re-checkin

              # work even if the previous checkin was less than a second ago.

				sleep(1);

				$self->checkout( $station, 1 );

             # XXX same workaround: We can't checkin immediately after checkout.

				sleep(1);

			}

			my $success = $self->app->checkin_query->execute(

				$self->get_user_id,

				$self->get_station_id(