Question

I want to make a after_update callback only execute when a certain configuration parameter is true.
At first I had something like this:

after_update :do_something
...

def do_something
  return unless MyApp::Application.config.some_config
  actualy_do_something
end

But then I thought, why not make the callback assignment conditional?
Like this:

after_update :do_something if MyApp::Application.config.some_config

However I don’t fully understand what Im doing here. When would this change? Only on server restarts? How do I test this behavior ? I can’t just set the config, the model file won’t be read again.

Please advise.

Answer 1

The standard way of achieving a conditional callback is to pass a symbol or proc to :if:

before_create :generate_authentication_token, :if => :authentication_token_missing?
after_destroy :deliver_thank_you_email, :if => lambda {|user| user.wants_email? }

def authentication_token_missing?
  authentication_token.empty?
end

This format could also reference a global configuration setting on Rails.configuration

after_update :refresh_cache, :if => :cache_available?

def cache_available?
  Rails.configuration.custom_cache.present?
end

This would allow the behavior of the application to change without having to restart the server or remove a constant and reload the file.