appointment.rb

class Appointment < ActiveRecord::Base
  attr_accessible :booking_resource_id, :boooking_id, :customer_id
  
belongs_to :customer
belongs_to :booking

end

booking.rb

class Booking < ActiveRecord::Base

has_many :booking_resources
has_one :appointment
has_one :customer, :through => :appointment

attr_accessible :approved, :approvedBy, :note, :end, :start, :title, :customer_id, :booking_resource_id

validates :start, :end, :overlap => {:scope => "booking_resource_id"}

  def start_cannot_be_future
      if self.start > self.end
        errors.add(:start, "Date can't be in the future")
      end
  end

end

booking_resource.rb

class BookingResource < ActiveRecord::Base
  attr_accessible :name, :color

  belongs_to :booking

  validates :name, :uniqueness => true
end

customer.rb

class Customer < ActiveRecord::Base
  attr_accessible :address, :city, :company, :fname, :lname, :state, :zip
  has_many :bookings, :through => :appointments
end

gistfile1.txt

1.9.3-p194 :009 > BookingAppointment
 => BookingAppointment(id: integer, customer_id: string, booking_id: string, booking_resource_id: string, created_at: datetime, updated_at: datetime) 

1.9.3-p194 :003 > @booking = Booking.find(2)
  Booking Load (0.3ms)  SELECT "bookings".* FROM "bookings" WHERE "bookings"."id" = ? LIMIT 1  [["id", 2]]
 => #<Booking id: 2, start: "2012-12-10 00:00:00", end: "2012-12-18 00:00:00", approved: false, approvedBy: "", customer_id: 1, booking_resource_id: 2, created_at: "2012-12
-10 01:22:40", updated_at: "2012-12-16 07:07:31", title: "asdf", ipads: nil, note: nil> 

1.9.3-p194 :004 > @app = BookingAppointment.find(1)
  BookingAppointment Load (0.2ms)  SELECT "booking_appointments".* FROM "booking_appointments" WHERE "booking_appointments"."id" = ? LIMIT 1  [["id", 1]]
 => #<BookingAppointment id: 1, customer_id: "1", booking_id: "2", booking_resource_id: "2", created_at: "2012-12-24 01:27:23", updated_at: "2012-12-24 01:58:30"> 

1.9.3-p194 :005 > @app.booking
  Booking Load (0.2ms)  SELECT "bookings".* FROM "bookings" WHERE "bookings"."id" = 2 LIMIT 1
 => #<Booking id: 2, start: "2012-12-10 00:00:00", end: "2012-12-18 00:00:00", approved: false, approvedBy: "", customer_id: 1, booking_resource_id: 2, created_at: "2012-12
-10 01:22:40", updated_at: "2012-12-16 07:07:31", title: "asdf", ipads: nil, note: nil> 

1.9.3-p194 :006 > @app.customer
  Customer Load (0.2ms)  SELECT "customers".* FROM "customers" WHERE "customers"."id" = 1 LIMIT 1
 => #<Customer id: 1, company: "Big Inc", fname: "Joe", lname: "Shmoe", address: "123 cool st", city: "Orlando", state: "fl", zip: "32746", created_at: "2012-12-09 21:01:02
", updated_at: "2012-12-09 21:01:02"> 

1.9.3-p194 :007 > @app.booking_resource
  BookingResource Load (0.3ms)  SELECT "booking_resources".* FROM "booking_resources" WHERE "booking_resources"."id" = 2 LIMIT 1
 => #<BookingResource id: 2, name: "M2", created_at: "2012-12-16 07:05:24", updated_at: "2012-12-16 07:05:24", color: "green">