Un petit exemple de DataMapper

Player.rb

class Player 

    include DataMapper::Resource

    property :id,                 Integer, :key => true
    property :name,               String
    property :hfr_name,           String
    property :last_statistics_id, Integer

    has 1, :lastStatistics, 'Statistics',
        :parent_key => [ :id, :last_statistics_id ],
        :child_key  => [ :player_id, :id ]

    has n, :statistics, 'Statistics'

end