gistfile1.rb

class Table
   include DataMapper::Resource
   
   property :id, Serial
   property :name, String 
   
   # Relationship to the join table. 
   has n, :tableBookings
   
   # Defines that Table has bookings in :tableBookings on the :booking named relationship. (a)
   has n, :bookings, :through => :tableBookings, :via => :booking    
end

class Booking
  include DataMapper::Resource
  property :id, Serial

  has n, :tableBookings

  # Defines that Booking has tables in :tableBookings on the :booking relationship. (b)
  has n, :tables, :through => :tableBookings, :via => :table
  
  belongs_to :employee
  belongs_to :customer 
  
end  

class TableBooking
  include DataMapper::Resource
  property :serial, Serial
  property :table_id, Integer, :min => 1 # (a)
  property :booking_id, Integer, :min => 1 # (b)
  
  belongs_to :table # (a)
  belongs_to :booking # (b) 
              
end