A presentation delivered to the Ruby on Rails Oceania Melbourne group's October meet up. Covers how to cleaning organise controller code with object proxying to play well with fragment caching in the views

1. Lazy Loading
..and object proxying shenanigans

2. John Barton
www.whoisjohnbarton.com
@johnbarton

3. we’re often* hiring
* a month or two ago, right now, a couple of months from now

4. The Problem:

5. To handle ever increasing
page load through the
judicious application of view
fragment caching...

6. ... without resorting to
downright ugly code

7. For Example:

8. class PostController < ApplicationController
def index
@posts = Post.all
end
end

9. <% @posts.each do |post| %>
<%= post.title %>
<% end %>

10. Make it fast:

11. <% cache 'slow_posts' do %>
<% @posts.each do |post| %>
<%= post.title %>
<% end %>
<% end %>

12. What now?

13. class PostController < ApplicationController
def index
@posts = Post.all
end
end
@posts = Post.all is still
evaluated ... and it’s expensive

14. What about?
<% cache 'slow_posts' do %>
<% Post.all.each do |post| %>
<%= post.title %>
<% end %>
<% end %>

15. Separation of concerns?

16. What about?
class PostController < ApplicationController
def index
unless fragment_exist? 'slow_posts'
@posts = Post.all
end
end
end

17. Separation of concerns?

18. What About?
class PostController < ApplicationController
def index
@posts = lazy_load { Post.all }
end
end

19. Still not perfect ... but
fuck it ... I’ve got a job
to get on with

20. How?

21. def lazy_load(&block)
LazyLoader.new(&block)
end

22. class LazyLoader
instance_methods.each { |m| undef_method m unless m =~ /^__/ }
def initialize(&block)
@_initializer = block
end
protected
# pass everything to _target
def method_missing(method, *args, &block)
_target.send method, *args, &block
end
private
# on first call will instantiate itself with _initializer
block
def _target
@_target ||= @_initializer.call
end
end

23. Gotchas:

24. ... or when I realised I
wanted to be a
Smalltalk programmer

25. class PostController < ApplicationController
def show
@post = Post.find(params[:id])
end
end
<% if @post %>
<%= @post.title %>
<% end %>

26. class PostController < ApplicationController
def show
@post = lazy_load { Post.find(params[:id]) }
end
end
<% cache 'slow_post' do %>
<% if @post %>
<%= @post.title %>
<% end %>
<% end %>

27. NoMethodError:
undefined method `title'
for nil:NilClass

28. wtf?

29. Ruby’s boolean operators don’t ask
the objects for their truthyness
Word on the street is Smalltalk has that covered*
* I don’t know Smalltalk so hopefully I’m not full of shit right here

30. a = lazy_load { nil }
# this is fine
nil.nil? # => true
a.nil? # => true
# this is broken but.....
# i can fix it by opening up NilClass
a == nil # => true
nil == a # => false
# but what do i do about these?
!!nil # => false
!!a # => true
if a
puts "blah!"
end # => "blah!"

31. Two Solutions:

32. <% cache 'slow_post' do %>
<% unless @post.nil? %>
<%= @post.title %>
<% end %>
<% end %>
OR
Learn Smalltalk

33. http://github.com/joho/lazy-loader
we’re pretty frickin rad, come work for us