Interesting Things

• ActiveRecord's #method_missing takes precedence over private methods, which means you cannot simply mark "private" database-derived attributes.
  code:

  # File: app/models/rock_star.rb
  #
  # == Schema Information
  # Schema version: 1
  #
  # Table name: rock_stars
  #
  #  id            :integer         not null, primary key
  #  real_name     :string(255)     
  #  band_name     :string(255)     
  #  personal_life :string(255)     
  #
  
  
  class RockStar < ActiveRecord::Base
    def method_missing(method, *arguments, &block)
      puts "I see you've sent my #{method} back and my ActiveRecords and they're all scratched"
      super
    end
  
  
    private
  
  
    def personal_life=(arg)
      puts "Vanish in the air you'll never find me"
      attributes[:personal_life] = arg
    end
  end
  

  script/console:

  Loading development environment (Rails 2.0.2)
  >> sting = RockStar.new(:real_name => 'Gordon Sumner', :band_name => 'The Police')
  I see you've sent my real_name= back and my ActiveRecords and they're all scratched
  => #<RockStar id: nil, real_name: "Gordon Sumner", band_name: "The Police", personal_life: nil>
  >> sting.personal_life = "I'll be watching you"
  I see you've sent my personal_life= back and my ActiveRecords and they're all scratched
  => "I'll be watching you"
  

  Potential solutions:

  • Convention... name "private" database attributes with leading underscores

  • Exception:

    class RockStar < ActiveRecord::Base
      def personal_life=(arg)
        raise "Protest is futile, nothing seems to get through"
      end
    end
    

  • Have another? Post a comment.

• ||= ("or equal") blows up you have a public "writer", but a private "reader"; makes sense, but still worth a mention.
  code:

  class Model < ActiveRecord::Base
    def field_name=(arg)
      @field_name = arg
    end
  
  
    private
  
  
    def field_name
      @field_name
    end
  end
  

  script/console:

  Loading development environment (Rails 2.0.2)
  >> instance = Model.new
  => #<Model id: nil, field_name: nil>
  >> instance.field_name = 'lala'
  => "lala"
  >> instance.field_name ||= 'dodo'
  NoMethodError: private method `field_name' called for #<Model:0x17df6d0>
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.0.2/lib/active_record/attribute_methods.rb:205:in `method_missing'
    from (irb):4
  

• ActiveRecord writers always return the passed in argument, even if you define some other return value. This also makes sense -- necessary for chaining, etc., but what the heck...
  code:

  class Model < ActiveRecord::Base
    def field_name=(arg)
      @field_name = arg            
      return "custom return value"
    end
  end
  

  script/console:

  Loading development environment (Rails 2.0.2)
  >> instance = Model.new
  => #<Model id: nil, field_name: nil>
  >> instance.field_name = 'lala'
  => "lala"