class Airplane
  attribute :id
  attribute :capacity, Integer
  attribute :model_number, Integer
  attribute :registration_number, Integer
  attribute :weight, Integer
  attribute :plane_type

  belongs_to :hanger
  belongs_to :owner
  has_many :maintenances
end

class Maintenance
  attribute :id
  attribute :work_code, String
  attribute :ended_at, DateTime
  attribute :started_at, DateTime
  belongs_to :airplane
  belongs_to :employee

  def hours
    ended_at - started_at
  end
end

class Hanger
  attribute :id
  attribute :capacity, Integer
  attribute :location, String
  attribute :number, Integer
  belongs_to :employee
end

class Owner
  attribute :id
  attribute :name
  attribute :address
  attribute :telephone_number
end

class Person < Owner
  attribute :social_insurance_number
end

class Pilot < Person
  attribute :license_number
  has_many :restrictions

  def airplanes
  end
end

class Employee < Person
  attribute :salary, Float
  attribute :shift, Integer
  has_many :plane_types
end

class Corporation < Owner
end

class Restriction
  attribute :id
  attribute :description, String
end