class User < ActiveRecord::Base

  has_many :device_ownerships
  has_many :devices, :through => :device_ownerships

class Device < ActiveRecord::Base
  has_one :device_ownership
  has_one :user, :through => :device_ownership
end


class DeviceOwnership < ActiveRecord::Base
  belongs_to :user
  belongs_to :device
end

def create
  user = User.create
  device = Device.create
  device_ownership = DeviceOwnership.create(:serial_numer => params[:device_serial_number], :device_id => device.id, :user_id => user.id)
end