How to check modified value in a model's before_save callback?

Question

How can I read the value that a controller has set in a before_save callback?

Example:

I have a model with a url field. Before saving, I want to check if the url was changed. If so, do some stuff with both the new and old url.

Is that possible?

Answer 1

Try something like this:

before_save { |m| if m.url_changed? ... }

Also see the docs on ActiveModel::Dirty

Answer 2

better way

before :todo, if: :first_name_or_last_name_changed?

and your todo method

def first_name_or_last_name_changed?
   first_name_changed? || last_name_changed?
end

Answer 3

If it has changed it should be in the params hash. If it hasn't changed it shouldn't be in there. Therefore, you can put this custom handling into the controller, or in a method on the model that does this.

If you really want to access it inbefore_save check the documentation on ActiveRecord callbacks, and you will see how to access the before and after values.