Lazy Loading and Object Proxying Shenangians

Lazy Loading..and object proxying shenanigans

John Bartonwww.whoisjohnbarton.com

@johnbarton

we’re often* hiring

* a month or two ago, right now, a couple of months from now

The Problem:

To handle ever increasing page load through the

judicious application of view fragment caching...

... without resorting to downright ugly code

For Example:

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

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

Make it fast:

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

What now?

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

@posts = Post.all is still evaluated ... and it’s expensive

What about?

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

Separation of concerns?

What about?

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

Separation of concerns?

What About?

class PostController < ApplicationController def index @posts = lazy_load { Post.all } endend

Still not perfect ... but fuck it ... I’ve got a job

to get on with

How?

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

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 endend

Gotchas:

... or when I realised I wanted to be a

Smalltalk programmer

<% if @post %> <%= @post.title %><% end %>

class PostController < ApplicationController def show @post = Post.find(params[:id]) endend

<% cache 'slow_post' do %> <% if @post %> <%= @post.title %> <% end %><% end %>

class PostController < ApplicationController def show @post = lazy_load { Post.find(params[:id]) } endend

NoMethodError:undefined method `title'

for nil:NilClass

wtf?

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

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

Two Solutions:

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

OR

Learn Smalltalk

http://github.com/joho/lazy-loader

we’re pretty frickin rad, come work for us