Rails ActiveRecord: Locking down attributes when record enters a particular state

Question

Wondering if there’s a plugin or best way of setting up an ActiveRecord class so that, for example, when a record enter the "published" state, certain attributes are frozen so that they could not be tampered with.

Answer 1

If the particular state is merely persisted?, then attr_readonly is the best option.

attr_readonly(*attributes) public

Attributes listed as readonly will be used to create a new record but update operations will ignore these fields.

To test (courtesy of THAiSi):

class MyModel < ActiveRecord::Base
  attr_readonly :important_type_thingie
end

#RSpec
describe MyModel do
 its('class.readonly_attributes') { should include "important_type_thingie" }

 it "should not update the thingie" do
   m = create :my_model, :important_type_thingie => 'foo'
   m.update_attributes :important_type_thingie => 'bar'
   m.reload.important_type_thingie.should eql 'foo'
 end
end

Answer 2

Editing attributes which shouldn't be edited is a validation error:

class Post < ActiveRecord::Base
  validate :lock_down_attributes_when_published

  private

  def lock_down_attributes_when_published
    return unless published?

    message = "must not change when published"
    errors.add(:title, message) if title_changed?
    errors.add(:published_at, message) if published_at_changed?
  end
end

This uses the ActiveRecord::Dirty extensions introduced in 2.2 or so.