# Pastebin 0Y60FiGe
$ perl6 -MRed -e '
model Person { ... }
model Track {
   has UInt $!id is serial;
   has UInt $!person-id is referencing{ Person.name };
   has Person $.person is relationship{ .person-id };
   has Instant $.time is column;
}
model Person {
   has Str $.name is id;
   has Track @.tracks is relationship{ .person-id }

   method total {
      @!tracks.sort(*.time).map(*.time).batch(2).map({ .[1] - .[0] }).sum
   }
}


my $*RED-DB = database "SQLite";

Person.^create-table;
Track.^create-table;
#my $*RED-DEBUG = True;
my \fernando = Person.^create: :name<Fernando>;
fernando.tracks.create: :time(now - 2000);
fernando.tracks.create: :time(now - 1000);
fernando.tracks.create: :time(now - 500);
fernando.tracks.create: :time(now);


say fernando.total

'
1500.021592308574