Creating a Model - ruby-on-rails

Question

I want to create a model called 'Persona' (which belongs_to model User). The user chooses a name in a form and then clicks the create button, so I need the attribute 'name' in the Persona model. I also want the Persona model to have a lower case version of the persona's name, so I need a second attribute 'downcase_name'. For example, the user may choose the persona's name to be Fooey Barman, so the downcase_name would be fooey barman.
My questions is, how do you initialise the downcase_name attribute? Do you put it in the Persona controller? In the new or create methods? Something like:
def create
#persona = Persona.new(persona_params)
#persona.downcase_name = #persona.name.downcase
if #persona.save
flash[:success] = "Welcome, " + #persona.name
redirect_to #persona
else
render 'new'
end
end
Or do you put it in the model?
class Persona < ActiveRecord::Base
before_create :make_downcase_name
validates :name, presence: true, length: { maximum: 50 }
private
def make_downcase_name
self.downcase_name = name.downcase
end
end
Or perhaps like this?
class Persona < ActiveRecord::Base
validates :name, presence: true, length: { maximum: 50 }
validates :downcase_name, presence: true
end
EDIT:
So, am I right in thinking the way to do it is in the model, with a before_save and a validation, like this?:
class Persona < ActiveRecord::Base
before_save :make_downcase_name
validates :name, presence: true, length: { maximum: 50 }
validates :downcase_name, presence: true
private
def make_downcase_name
self.downcase_name = name.downcase
end
end

Answer 1

The use of the before_* callback seems pretty idiomatic. Alternatively, you can also have a service object created in the controller (say PersonaCreator) that would handle the logic and set the appropriate attributes on the model.
Note that before_create will be called only once, meaning that if the user changes the persona's name later, the callback will not be called. You might want to do something like before_save and check whether the name has been changed.