How would I build a better relationship? Whenever I create a license for a person, I have to pass in a vehicle relation too.

relations.rb

class Vehicle
    include DataMapper::Resource

    property :id,               Serial
    property :registration,     String,  required: true
    property :make,             String,  required: true
    property :type,             Enum[:saloon, :mpv], default: :saloon # anything above 4(passengers) == :mpv
    property :date_of_reg,      Date,    required: true
    property :number_of_seats,  Integer, required: true
    property :driver_1,         Integer, required: true
    property :driver_2,         Integer
    property :owner_id,         Integer
    property :owner_type,       Enum[:person, :organisation], default: :person

    property :created_at, DateTime
    property :updated_at, DateTime

    has n, :licenses
    has n, :mileages

    def driver
      Person.get(self.driver_1)
    end

    def drivers
      Person.all(id: [self.driver_1, self.driver_2])
    end

    def owner
      type = self.owner_type
      raise  OwnerTypeError, 'The owner_id or owner_type are not available' unless type

      case type
      when :organisation
        driver = Organisation.get(self.owner_id)
      when :person
        driver = Person.get(self.owner_id)
      end

      driver
    end
  end #Vehicle
  
  ###---Error Class --
  class OwnerTypeError < StandardError
  end #OwnerTypeError
  
  
  class License
    include DataMapper::Resource

    property :id, Serial
    property :number, String , required: true
    property :provider, String, required: true
    property :starts_on, Date, required: true
    property :expires_on, Date, required: true
    property :type, Enum[:driving, :insurance, :mot, :road_tax], default: :driving
    property :active, Boolean, default: false

    belongs_to :person, required: false
    belongs_to :vehicle, required: false
    # belongs_to :company
  end
  
  p = Person.get(1)
  v = p.linceses.create!(number: 'KILO123RG', provider: 'DVLA', starts_on: Date.today, expires_on: Date.today + 135, active: true)
  
  v.errors # => DataMapper::SaveFailure, vehicle_id cannot be blank