# Pastebin m22K8ThX
MacBook-Pro-de-Fernando:BestTree fernando$ cat Tree.pm6 
use Red;

class X::Tree::ExistsInTheSameArea is Exception {
    has Rat $.longitude;
    has Rat $.latitude;

    method message { "A tree on ($!longitude, $!latitude) was already suggested" }
}

model Tree {
    has UInt    $!id            is id;
    has Rat     $.latitude      is column;
    has Rat     $.longitude     is column;
    has Rat     $.height        is column;
    has Str     $.description   is column;

    ::?CLASS.^add-unique-constraint: { .latitude, .longitude };

    method all-trees {
        self.^all.sort: -*.height
    }

    method find-tree(Rat $longitude, Rat $latitude) {
        self.^find: :$longitude, :$latitude
    }

    method suggest-tree(Rat $longitude, Rat $latitude, Rat $height, Str $description) {
        CATCH {
            die X::Tree::ExistsInTheSameArea.new: :$longitude, :$latitude
        }
        self.^create: :$longitude, :$latitude, :$height, :$description
    }
}
MacBook-Pro-de-Fernando:BestTree fernando$ perl6 -I../Red2/lib/ -MRed -I. -MTree -e '

my $*RED-DB = database "SQLite"; Tree.^create-table;

Tree.suggest-tree: 1.1, 2.2, 3.3, "bla";
Tree.suggest-tree: 1.1, 2.2, 3.4, "ble";

'
A tree on (1.1, 2.2) was already suggested
  in method suggest-tree at -e line 29
  in block <unit> at -e line 6

MacBook-Pro-de-Fernando:BestTree fernando$