In Rails, how do I limit which attributes can be updated, without preventing them from being created?

Question

I have a situation where an attribute can be created through a JSON API. But once it is created, I want to prevent it from ever being updated.

This constraint causes my

Answer 1

You can use attr_readonly, this will allow the value to be set on creation, but ignored on update.

Example:

class User < ActiveRecord::Base
  attr_accessible :name
  attr_readonly :name
end


> User.create(name: "lorem")
> u = User.first
=> #
> u.name = "ipsum"
=> "ipsum"
> u.save
=> true
> User.first.name
=> "lorem"