Should I deny editing entries using a filter in my controller or callback in my model?

Question

To maintain data integrity, I need to prevent some models from changing after certain events. For example, you cannot sell a product after it is sold.

I always implemented this in the controller, for example (pseudo-code):

def ProductsController < ApplicationController
  before_filter require_product_not_sold, :only => [ :write_off ]

private
  def require_product_not_sold
    if @product.sold?
      redirect_to @product, :error => "You can't write off a product that has been sold"
    end
  end
end

It just seemed to me that I, too, could do this in a model. Something like that:

def Product < ActiveRecord::Base
  before_update :require_product_not_sold

private
  def require_product_not_sold
    if self.written_off_changed?
      # Add an error, fail validation etc. Prevent the model from saving
    end
  end
end

Also think that there may be several different events that require the product to not be sold.

I like the approach to the controller - you can set meaningful flash messages, and not add verification errors. But it looks like this code should be in the model (for example, if I wanted to use the model outside of my Rails application).

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:)

Answer 1

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