gistfile1.rb

  validates :enrollment_method,
    presence: true,
    inclusion: {
      in: ['email', 'phone_number']
    }

  validates :email,
    presence: true,
    format: { 
      with: /\A[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]+\z/, 
      message: "is not of the correct format"},
    if: lambda { |device|
      device.enrollment_method == 'email'
    }

  validates :phone_number,
    presence: true,
    format: {
      with: /^[\D]*1?([\D]*[\d][\D]*){10}[\D]*$/, # 10 digits in string, optionally starts with "1" to make 11.
      message: "is not a valid US phone number"},
    if: lambda { 
      |device| device.enrollment_method == 'phone_number' }