Dynamic validations

validations.rb

class MyModel
  include ActiveModel::Model

  attr_accessor :name, :email, :options

  def initialize(attributes = {})
    super
    @options ||= {}
  end

  # Class-level validations
  validates :name, presence: true
  validates :name, length: { minimum: :name_length, if: :validate_name_length?}
  validates :email, presence: true, format: { with: URI::MailTo::EMAIL_REGEXP }

  def validate_name_length?
    !!name_length
  end

  def name_length
    options[:name_length]
  end
end

puts (m = MyModel.new(name: 'John Doe', email: '[email protected]', options: {name_length: 10})).valid? # => false
puts (m2 = MyModel.new(name: 'John', email: '[email protected]', options: {name_length: 2})).valid? #= true
puts (m3 = MyModel.new(name: 'John', email: '[email protected]')).valid? #= true