Weixuhong.com

 
class Model < ActiveRecord::Base
  before_update :disallow_bob
 
  def disallow_bob
  return false if model.name == "bob"
  end
end
 
class ModelObserver < ActiveRecord::Observer
  def before_update(model)
    return false if model.name == "mary"
  end
end
 
m = Model.create(:name => "whatever")
 
m.update_attributes(:name => "bob")
=> false -- name will still be "whatever" in database
 
m.update_attributes(:name => "mary")
=> true -- name will be "mary" in database