doctor.rb

class Doctor < ActiveRecord::Base
	attr_accessible :name, :phone, :province_id

	has_many :schedules, :dependent => :destroy
	has_one :province
end

province.rb

class Province < ActiveRecord::Base
  attr_accessible :name
  has_many :schedules
  has_many :doctors
end

schedule.rb

class Schedule < ActiveRecord::Base
	attr_accessible :doctor_id, :date, :province_id

	belongs_to :doctor
	belongs_to :province

	validates_uniqueness_of :province_id, :scope => :date
end