Form Model object like this: http://www.paperplanes.de/2012/12/6/form-objects-with-activemodel.html but with Virtus.

form_model.rb

# Example:
#
# class EditForm < FormModel
#   model :a
#
#   attribute :title, String
#
#   validates :title, presence: true
# end
#
# a = A.first
#
# f = EditForm.new(a)
# f.valid?
# # => false
#
# f.title = "A Title"
# f.valid?
# => true
#
# f = EditForm.new(a, title: "Some Title")
# f.valid?
# # => true
#
class FormModel
  include Virtus
  Boolean = Virtus::Attribute::Boolean # fixes Virtus boolean mapping

  extend ActiveModel::Naming
  include ActiveModel::Conversion
  include ActiveModel::Validations

  def self.model(model = nil)
    return @model unless model
    @model = model
  end

  def self.model_name
    ActiveModel::Name.new(model.to_s.classify.constantize)
  end

  def initialize(model, attributes = {})
    super(attributes)
    @model = model
  end

  def model
    @model
  end

  def to_key
    model.to_key
  end
end