Custom Rails Callback

onkis (Mike Ball) — Thu, 13 Mar 2008 16:28:28 GMT
// 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
DZone Snippets: Onkis's Code Snippets

Custom Rails Callback
