Prevent change of one field in Rails model

Question

I have two related models - let\'s say Activity and Step. Activity has_many :steps and Step belongs_to :activity which me

Answer 1

I think you can do this too with the Hobo permissions system: http://hobocentral.net/manual/permissions

For example:

def update_permitted?
  acting_user.administrator && !activity_id_changed?
end