Custom Rails Callback
// This shows you how to extend active record to allow a custom callback.
#ever needed to add your own callback into the active record callback chain? #here's how... module ActiveRecord #to keep things clean we'll define our own module module SweetCustomCallbacks #this is the ruby method that is called when you call include on a module #the method passed, base in our case, is the class your including yourself in def self.included(base) #this clas_eval method takes a block that will be added to base, which is ActiveRecord::Base #basically this is like writing code directly into the class ActiveRecord::Base base.class_eval do #alias_method_chain is very cool #it allows us override a method without removing the original and without the original knowing its been changed #here's how it works: # 1st argument is the name of the method you're overriding # 2nd argument is feature you want to add # so if create_or_update is called it will actually call create_or_update_with_sweet_custom_callbacks # the original is still avaliable at create_or_update_without_custom_callbacks alias_method_chain :create_or_update, :sweet_custom_callbacks #the method create_or_update is an internals method to ActiveRecord that is called whenever you call .save or .update #this is the class method that allows the cool syntax: # class Article < ActiveRecord::Base # before_before_save :add_authors_name #private #def add_authors_name #..... def self.before_before_save(*callbacks, &block) callbacks << block if block_given? #add the block to the array of callback functions if a block was passed write_inheritable_array(:before_before_save,callbacks) end end end #the instance method, although not recomended is avaliable for overriding #also if you wanted to have a callback that always did something say add the users's id to the object #you could always code that in here and remove the class above def before_before_save() end #ok this is the method that is now called instead of create_or_update #it calls a method callback on def create_or_update_with_sweet_custom_callbacks return false if callback(:before_before_save) == false #this method does all the real work and calls the callback function in callbacks.rb that gets the methods and runs them create_or_update_without_sweet_custom_callbacks end end class Base include SweetCustomCallbacks #include our module in ActiveRecord::Base end end
