Gotchas of internal iFrame facebook apps and external web apps using Facebooker gem

A while back, I added mobtropolis to facebook as an internal app. I decided to go with using FBML because there was more support in the how-tos about how to use it, and it looked like tighter look and feel and integration.

However, unlike many facebook apps, Mobtropolis also exists as a stand-alone external web app. This decidedly made things a little bit hairier, and I had to write a custom mime-response filter to be able to tell whether a call was coming from a web client (HTML), or as an internal facebook app (FBML), in order to authenticate correctly. I also ended up having to write some custom testing methods for it as well.

Then I revamped the layout of mobtropolis.

It's major suckage to have to maintain two separate views, so I decided to go with an iFrame with the internal facebook app. It took a bit of work to convert it to use iFrames, because authentication gets a little bit more complicated. However, it's something that I only have to deal with once. Subsequent changes to the layout won't affect it as much.

In retrospect, I should have went with using an iFrame from the beginning, though, at the time, mobtropolis was fairly ugly. This is what people call "judgement", and I made the mistake and it cost me about three weeks. The thing is, you just make the best decision you can at the time, and make sure you can change directions easily.

There were a couple gotchas when using iFrames.

1. Double facebook frames on redirect to install page.
   
2. External app's layout is wider than iFrame
   
3. Facebook only sends fb params on the first call to your app
   

Hopefully, I'll save you some time, to whomever's looking for this info.

1) Double facebook frames

When you use ensure_application_is_installed_by_facebook_user or ensure_authenticated_to_facebook, it will automatically reroute the user to an install page if he didn't install your application. Problem is, it assumes that you're not in an iFrame. It ends up that you can override application_is_not_installed_by_facebook_user in your controllers.

def application_is_not_installed_by_facebook_user
  redirect_to add_internal_facebook_app_url
end

Where add_internal_facebook_app_url is an action in a controller (say, my_controller), that renders javascript to change the location of the top frame.

def add_internal_facebook_app
  render :layout => false, :inline => %Q{<script type="text/javascript">
    top.location.href = "<%= session[:facebook_session].install_url -%>"
    </script>}
end

You have to make sure you connect it as a route in order to redirect it like I did in the overridden application_is_not_installed_by_facebook_user(), in routes.rb under config/

map.add_internal_facebook_app('add_facebook_internal_app',
                              :controller => "my_controller",
                              :action => "add_internal_facebook_app")

2) External app is wider than iFrame

I think there is a way to resize the Facebook iFrame, but I didn't find out about it after I did this. By default, the Facebook iFrame "smartsizes" itself, to fill out rest of the page.

First, I created a stylesheet called fb_internal_layout.css, that had extra stylings that squeezed the interface in a 446px wide iFrame. Then I included it in the headers of my layouts as:

<link href="fb_internal_layout.css" id="fb_internal_layout" media="screen" rel="alternate stylesheet" title="Facebook Internal Layout" type="text/css" />

Make sure you include titles in the link, so that you can actually switch it out.

Then we use javascript to turn on or off this alternate stylesheet depending on whether we're in an iframe or not. You can use something like what's described in A List Apart's article on alternate stylesheets to switch out stylesheets.

To detect if I was in an iFrame, I simply checked whether (frames.top == frames.self). If it was, I turned on the alternate stylesheet.

3) Facebook only sends fb params on the first call to your app

This is actually not a problem if you use FBML. This is also not a problem if you're using iFrames, and you require a user to install your facebook app if they want to see what's on it.

However, even though this is how a lot of facebook apps operate, I don't think this is very user friendly. The user has no way to judge whether they want to install your app or not if they can't even sample it. I would rather have a user add an app because they want to, rather than getting people that add it, but then remove it shortly after. This not only gives you an inaccurate indication of how many people really want to use your app, but also annoys the hell out of them.

But making some pages of an iFrame app to be public is a bit tricky. Only the first click into your facebook app is there fb_params in the request. Every subsequent click by a user is in your iFrame, so looks as if the user is actually on the external webpage.

There are a couple solutions, but I ended up storing session state that the user made a request from an internal app before. You can't override params on subsequent requests, so using old fb_params to authenticate is difficult at best. Using the flag that a user made a request before, this session is likely to be coming from an internal facebook app. When it comes upon a private page, it should be redirected to install mobtropolis, using 1) detailed above. This is not a perfect solution, but it covers all cases correctly.

This, however, doesn't account for the instance where a user that already installed. In that particular case, I just went ahead an got a facebook session on every first request to the facebook app.

Hope that helped, and I hope never to have to mess with this sort of stuff again, and that you don't either. More interesting posts in the future. Tip!

Foxy Fixtures and polymorphic tables

Well, I'm behind on everything, which means a bunch of interesting blog posts are queued up. But this one seemed short enough to warrant a small post.

I've always hated fixtures for the same reason that other people hate them, but nonetheless, I've bit the bullet to use them. Along comes Rails 2.0's foxy fixtures, and it becomes a little easier.

What it doesn't detail, however, is how to use your newly foxy fixtures for polymorphic models. If I have a vote model that I can use to vote on any type of table, with the old fixtures, I'd have:

my_vote:
  id: 1
  account_id: 1
  votable_id: 3
  votable_type: "Scene"

Normally, you just get rid of the foreign keys since it now checks the belongs_to associations of each model, and you can just use the label names. Same goes with the primary key id. It'll be autogenerated based on a hash of the fixture label.

my_vote:
  account: my_account
  votable: eat_hotdog
  votable_type: "Scene"

Note that you're using the association names, and NOT the foreign key name, so you don't use "_id" anymore (that bit me in the ass for a little bit).

However, you'll find that with polymorphic models, you won't be able to do that. Searching around the good 'ole web lead me to find that Foxy Fixtures originally came from a plugin called Rathole, and at the very end of the README, it states:

Also, sometimes (like when porting older join table fixtures) you'll need to be able to get ahold of Rathole's identifier for a given label. ERB to the rescue:

Go John Barnette! That way, you can simply do this in your fixtures as a fall-back:

my_vote:
  account: my_account
  votable_id: <%= Fixtures.identify(:eat_hotdog) %>
  votable_type: "Scene"

Tip!

irb console tricks

irb Mix Tape — err.the_blog

Not a big entry, but I think worth posting because it pays to learn your tools. I've got no insights of my own to add. Someone else's tip!

Render_to_string only counts if failed

render_to_string followed by render issues - Ruby Forum

I was puzzled by this yesterday, and good thing I went to do something else instead of tearing my hair out. Came back fresh today and found this. Apparently, render_to_string normally doesn't count as a render--given that it succeeds. If it throws an exception for some reason, then it'll get count as a double render if you rendered elsewhere. Small tip!

How to find multiple file types using linux's "find"

I've always found *nix's "find" and "grep" rather hard to use. Not only are there different flavors of regular expressions to use, but mainly different syntax. For find, the directory you're searching for comes first. For grep, it comes last. To find the negation of something, you'd use "-not" and for grep it's "-v". pain.

Anyway, been trying to learn my tools better, and I found out how to grep and replace expressions across multiple files through emacs. Since rails uses all sorts of file extensions, naturally, I wanted to grep for find different files types. I had thought the -name options took regexs (it doesn't), so I had tried it in regex (no go)...only to find that it's something like this:

find . -name "*.rb" -o -name "*.rhtml"

the -o is the equivalent of a boolean "or". small tip...

Making sure extra tasks get run when installing plugins with Piston

When I graduated college, I was a EE major that could code. However, in hindsight, I don't think I was as good because I had no idea how to put together moderate sized systems or above. One of the things that I like about Rails is that they have a system for plugins. I was too uncouth to consider it before. Once you extract a plugin out, you essentially have to treat it as a separate library or package. This forces you to encapsulate, because it's a bit of a pain changing plugins. I know you can extract code out to DLLs or Gems, but I never did it because it seemed like I didn't need it--plus it was extra steps.

I eventually would want a programming language that lets me extract out libraries inside the language, and make its public interface RESTful, and auto-extern its path in SVN and whatever the equivalent is in distributed version control like git/darcs.

Recently, I've started using Piston. It's a ruby plugin manager that's essentially a wrapper around svn:externals. It's been pretty easy to use. In addition, my plugins won't get stale. However, when you install a plugin with piston, you only import the files. It doesn't actually execute the install.rb file, like /script/plugin install would. I'll try to see if I can submit a patch to piston later, but for now, simply run "install.rb" in the root of the plugin, and it should do the install for you. small tip!

Setting time in your fixtures

In your rails fixtures, you should be able to set the time dynamically. If you set your database to default to UTC, make sure you use:

post:
  id: 1
  body: "This is my witty post"
  created_on: <%= 3.days.ago.utc.xmlschema %>

Unless you want to wreck havoc in your test cases. tip!

Getting inline-block working across browsers

In mobtropolis, there's a gallery of pictures that I have to show. While, normally, it's not too hard showing them as inline elements, if you just have pictures, it gets a bit tougher if you have a bunch of stuff that you have to inline correctly. Sites like facebook solve the problem by using a fixed layout, so you know the width of the area you can work in, and can thus use a table.

When you have a stretchable layout, however, that doesn't work. And what you need to do is use CSS, "display: inline-block" The problem is, it doesn't have consistent support across browsers. Only Opera and Safari use "display: inline-block" and "display: inline-table" correctly. IE6 and Firefox both use "display: inline" only and don't recognize inline-table and inline-block.

So thank goodness for design blogs out there: Align List Items Horizontally with CSS . His solution is a bit of a work around, but it prevents me from writing any javascript when I didn't need to.

.ib-fix li { display:-moz-inline-box; -moz-box-orient:vertical;
             display:inline-block; vertical-align:top; word-wrap:break-word; }
* html .ib-fix li { display:inline; }
* + html .ib-fix li { display:inline; }
.ib-fix li > * { display:table; table-layout:fixed; overflow:hidden; }

I should add that you need to also add this to get it to work in IE6, and get rid of the weird padding on the left:

ul.ib-fix
{ 
  list-style: none inside none;
  padding: 0px;
}

Yay. small tip! As a bonus, I also found out about ie7.js, a javascript library that fixes incompatibilities in ie7 and ie6.

Getting rid of emacs 23 splash screen

Pretty Emacs Reloaded

The latest emacs 23 is pretty neat, but it noticeably has that splash screen in the beginning. It's generally good practice for an app not to present new users with just a blank screen. There's should be something there to say, 'hey, these are the next steps'.

That said, I've found it annoying, probably because I'm use to it not being there. So I've found that you can turn it off through this comment.

(setq inhibit-splash-screen t)

Just put that in your .emacs file in your home directory, and you're all set. tip~

Generating rdoc for gems that refuse to generate docs

I recently upgraded to capistrano 2.1, and it's woefully lacking in documentation. Jamis Buck had already picked a documentation coordinator about a month ago, but nothing seemed to be happening since.

So it was time to go dumpster diving in cappy code. I at least wanted to see what the standard variables were. To my surprise, there were some docs in code, but I couldn't generate it with

gem rdoc capistrano

For those of us that had never made a gem, all you have to do to force it to is to edit the associated specification for the gem (/usr/lib/ruby/gems/1.8/specifications/), and add

s.has_rdoc = true

Maybe if I dig enough stuff out of it, I'll pose some prelim documentation for cappy 2.1 and donate it to the documentation effort.

As an aside and musing, ideally, the code itself would be documentation. However, just because you're reading code, doesn't mean that you can get the overall picture of how to use it. Even if you filtered out the details, and saw just the class and method declarations, that still wouldn't be enough since you can't see how things fit together. I don't know what a good solution would be. The simplest API is often complex enough to be nearly useless without good documentation.

Small tip!

The user owns this and that

In most any community-based website, your users are creating objects. And sometimes, you'd only like to display them when they're owned by the user. Usually, it's easy enough to do the check based on the association in the template views.

  <% if @story.account == session[:member] %>
    <%= render :partial => "story"
  <% end %>

However, for the sake of perhaps over-reaching, but something more readable, we try:

class Story < ActiveRecord::Base
  belongs_to :account

  def owned_by?(user)
    self.account == user
  end
end

  <% if @story.owned_by?(session[:member]) %>
    <%= render :partial => "story"
  <% end %>

But this gets to suck, because you have duplicate code in different classes that are just slightly different due to association names. One way to solve it is to put it in a module, and include it in different classes. After all, that's what mixins are for.

module Ownership
  def owned_by?(user)
    self.account == user
  end
end

class Story < ActiveRecord::Base
  include Ownership
  belongs_to :account
  # blah blah blah
end

class Post < ActiveRecord::Base
  include Ownership
  belongs_to :account
end

Or alternatively, you can put it in the account, but in reverse. But now, you have to search through the associations of the owned ActiveRecord object.

class Account < ActiveRecord::Base
  def owns?(ar_object)
    ar_object.class.reflect_on_all_associations(:belongs_to).detect { |assoc|
      ar_object.send(assoc.name) == self
    } ? true : false
  end
end

I find the tertiary operator to be kinda ugly there, but it doesn't make sense to return the reflection object. Regardless, this lets you do:

  <% if session[:member].owns?(@story) %>
    <%= render :partial => "story"
  <% end %>

However, this doesn't work for self-associated AR objects, or objects that have two or more belongs_to to the same account. It relies on a unique belongs_to association for every object belonging to account. I'm not sure yet, which way's the better way to go, and in the end it probably doesn't matter as much, but I do like being able to say user.owns?(anything) for any object without really thinking about what the associations are. half-tip.

State change observer for ActiveRecord

When I started writing some code recently, I noticed that my controllers were getting fat. There was much to do, but there was a bunch of stuff in there that didn't have anything to do with actually carrying out the action--things like sending notifications. ActiveRecord already has observers to take action on certain callbacks. However, what I needed was to take actions on certain state transitions. Not seeing any immediate solutions in the Rails API, I decided to test myself and try writing one. I was bored too. So while I'm not sure if it was worth the time writing it, it certainly was kinda interesting. Here's what I came up with:

Just as a contrived example, let's say we are modeling the transmission of a car. It has three modes: "park", "reverse", "drive". We want to send a notification when a user tries to change it from "reverse" to "drive", but not when he tries to change it from "park" to "drive". If it didn't matter, and we just wanted to send notifications when the state changed to drive, we'd just use the observers that came with ActiveRecord. But since we do care where the state transition came from, here's what I came up with:

class CreateCarTransmission < ActiveRecord::Migration
  def self.up
    create_table :car_transmission do |t|
      t.column :engine_id, :integer, :null => false
      t.column :mode, :string, :null => false, :default => "park"
    end
  end

  def self.down
    drop_table :car_transmission
  end
end

class CarTransmission < ActiveRecord::Base
  include StateTransition::Observable
  state_observable CarTransmissionNotifier, :state_name => :mode
end

So then for my notifier I have:

class CarTransmissionNotifier < StateTransition::Observer
  def mode_from_drive_to_reverse(transmission)
    # send out mail and flash lights about how this is bad.
  end
end

And that's it. Whenever in the controller, I change the state from "reverse" to "drive", lights will flash and emails will be sent out condemning the action, and my controllers stay small and lean.

class CarController < ApplicationController
  def dismantle
    @car = Car.find(params[:id])
    @car.update_attribute :mode, "reverse"
    @car.update_attribute :mode, "drive"
  end
end

So where's the magic? It took a bit of digging around. There were two major things I had to do. I had to insert observers during initialization and I had to override setting of attributes to include an update to notify observers.

ActiveRecord doesn't exactly allow you to override the constructor. I don't think I tried too hard to mess around with it. Looking on the web, I happened upon has_many :through again, where he has some good tips that helped me through Rail's rough edges. While I didn't exactly follow his advice, I did find out about the call back, :after_initialize. It must be something new, because I don't see it in the 2nd edition of the Rails book, and the current official API doesn't list it. Other Rails API manuals seem to be more comprehensive, like RailsBrain and Rails Manual.

Then overridding attributes has always been a bit of a mystery. I found a listing of the attribute update semantics, which was helpful to figure out what I was looking for, but it was false, in that you can't use the first one (article.attributes[:attr_name]=value) to set an attribute. Looking in the Rails code for 1.2.3, it shows that attributes is a read_only hash. But it's right that you should override the second one (article.attr_name=value), since update_attribute() and update_attributes() depends on it.

Again, it ends up that the function I was looking for wasn't found in the official API as a method, other than a short mention in the description of ActiveRecord under Overriding Attributes, which makes it harder to find. Ends up that we can use write_attribute().

So that's pretty much it. Using some standard meta-programming like how plugins do it, you wrap it up, and it's pretty simple:

require 'observer'

module StateTransition
  module Observable
    class StateNameNotFoundError < RuntimeError
      def message
        "option :state_name needs to be set to the name of an attribute"
      end
    end

    def self.included(mod)
      mod.extend(ClassMethods)
    end

    module ClassMethods

      def state_observable(observer_class, options)
        raise StateNameNotFoundError.new if options[:state_name].nil?
        state_name = options[:state_name].to_s
        
        include Object::Observable

        define_method(:after_initialize) do 
          add_observer(observer_class.new)
        end

        define_method("#{state_name}=") do |new_state|
          old_state = read_attribute(state_name)
          if old_state != new_state
            write_attribute(state_name, new_state) # TODO yield the update method
            changed
            notify_observers(self, state_name, old_state, new_state)
          end
        end
      end

    end
    
  end

  class Observer
    def update(observable, state_name, old_state, new_state)
      send("#{state_name}_from_#{old_state}_to_#{new_state}", observable)
    rescue NoMethodError => e
      # ignore any methods not found here
    end  
  end

end

I had a difficult time figuring out how to define methods for an instance of a class. The only thing I came up with was to use define_method, or to include a module with instance methods in them. instance_eval() didn't work. The meta programming for ruby gets rather confusing when you're doing it inside a method--it seems hard to keep track of which context you're in.

So if you can make a use of this, great. If you think it's worth moving it into a plugin, let me know that too. If you know of a better way, by all means, let me know. tip!

Syntactic sugar for dealing with empty containers

In any web application, we're often just reading a collection of rows from the database and displaying it in the browser. Often times, we'll have code that looks like this:

<% unless @friends.empty? -%>
  <% @friends.each do |friend| -%>
    <li><%= h friend.username %></li>
  <% end -%>
<% else -%>
  No friends yet
<% end -%>

I don't know why, but this kinda gets to me, and doesn't look all that neat. I probably attribute it to having to upgrade and maintain a piece of C server code that was nested 8 or 9 layers deep all in one huge main(). It might be counter-productive, but I tried to see if I could do better.

<% if @friends.each do |friend| -%>
  <li><%= h friend.username %></li>
<% end.empty? -%>
  No friends yet
<% end -%>

Well, this is kinda nice in a way that it's only one hierarchy deep. When I look at it, one section is for what to display when there are elements in the list, and one is for when there isn't. I suppose your mileage may vary. However, I didn't like the "if" in front. It obscures the intent of displaying the list. So, in the pursuit of more counter-productivity and perhaps in the spirit of pseudo-altering the language, I tried this out:

<% @friends.each do |friend| -%>
  <li><%= h friend.username %></li>
<% end.empty do -%>
  No friends yet
<% end -%>

Well, that worked. I kinda like it. Since the message was so simple, I had wanted empty() to take a message, and just display it, but because it's a "%" and not a "%=", the message won't get displayed, so I had to do it in a block. In a way, it's almost like being able to write my own "else" statement. If I had used curly braces instead of "do/end", it might look pretty close. Here's the code for empty:

class Array
  def empty(message = "")
    if self.empty?
      return block_given? ? (yield message) : message
    end
  end
end

Like it? Hate it? Tip!

Unable to freeze rails due to problem in rake task

I think the current version of stable Rails is 1.2.3. For those of you using this version, rather than Edge Rails, there's a little gotcha in the rake tasks.

Since I'm on a shared host, it's good practice to freeze your version of rails into the vendor's directory. You do this by using a rake task, per "rake rails:freeze:gems" But before you do that, if you're using SVN, you'll want to use "svn delete" to remove the vendors/rails directory. None of the rake tasks use SVN delete. They all use "rm -rf", which in my experience makes SVN freak out if the .svn directory is gone.

However, even with that done, freezing a new version of gems was failing.

It was looking for rails version 1.4.0, and not being able to install it. And even worse, when you try to run rake again, it said it couldn't find it!

Well, the latter was simple. A failed freeze leaves a blank vendor/rails directory, and if you look in 'config/boot.rb', it says:

if File.directory?("#{RAILS_ROOT}/vendor/rails")
require "#{RAILS_ROOT}/vendor/rails/railties/lib/initializer"
else
require 'rubygems'
...blah blah blah..
So make sure you remove vendor/rails.

The latter took a little bit of work digging around the rake tasks, and though it wasn't hard, I wasted about an hour. It ends up that the culprit is that the default rake task uses Gem.cache.search('rails'), which returns all gems with the name 'rails' in it.

I have a couple gems installed with the word 'rails' in it.

rails (1.2.3, 1.2.0, 1.1.6)
rails_analyzer_tools (1.4.0)
railsbench (0.9.2)

So it took the latest one, which was 1.4.0, and tried to install rails 1.4.0, which doesn't exist!

To hot fix it, the railities/lib/tasks/framework.rake file, under the freeze namespace and gems task, change "Gem.cache.search" to "Gem.cache.find_name"

That way, it only finds 'rails', and not all the other games with 'rails' in the name of the gem. This problem is solved in edge Rails, so no need to submit a patch. Tip!

Is preloading child tables always a good idea?

Optimization isn't something you should do too early on, but I think a little house cleaning every so often to make sure your pages aren't ridiculously slow is healthy. With any optimization task, you'd want to benchmark the results and see if there's an actual gain. The very basic tool for benchmarking is the ordinary script/performance/benchmark. The easiest to find analysis tools is the rails_analyzer gem. The last time I used rails analyzer, it wasn't that easy to use. The command line arguments seemed arcane. But its bench tool, which can benchmark controllers as opposed to just object models, is fairly easy to use.

Using the bookmarking example from before, let's say you have something like:

class SceneController < ApplicationController
  def list
    @books = Book.find_books
  end
end

class Book < ActiveRecord::Base
  def self.find_books
    find(:all, :include => [:bookmarks], 
               :conditions => ["books.created_on > ?", 6.month.ago])
  end

  def bookmarked_by?(user)
    self.bookmarks.select { |bm| bm.owner_id == user.id }.empty? ? false : true
  end
end

In the listing of books, one would display whether it's actually bookmarked by a user or not. Normally, without the :include, the listing would make repeated queries to the DB every time it displayed a book list element, since it will use bookmarked_by?(user_id) to determine if a user bookmarked the book. So instead of just 1 query, it would make n + 1 queries.

Preloading child tables isn't necessarily wise all the time. It really depends on what you intend to do with the data after you fetch it. As the Agile rails book warns, preloading all that data will take time. If you look at your log files, you'll see that it's a significant amount.

If you're only going to load a limited number of these book list elements on a single page at a time, it actually might make sense to forgo preloading of child tables, and just use a find() instead of a select.

class SceneController < ApplicationController
  def list
    @books = Book.find_books
  end
end

class Book < ActiveRecord::Base
  def self.find_books
    find(:all, :conditions => ["created_on > ?", 6.month.ago], 
         :limit => 20, :order => "created_on desc")
  end

  def bookmarked_by?(user)
    Bookmark.find(:first, 
                  :conditions => ["book_id = ? and owner_id = ?", id, user.id]) ? true : false
  end
end

And if you're going to display counts of arrays, but all means, use counter caching. It's easy to do (as long as you follow instructions!), for most situations.

Intuitively, if you want to display over a certain n number of book list elements, it makes more sense to use :include and select it. However, I wanted to point out that when you make decisions like this, you'll always want to measure the load times, because you earn what you measure.

Also, use the right number of runs. Too short number of a number of times you run a function, the more variation you'll have in your benchmarks. Let's say that you get two numbers for two different methods.

$ bench -u http://localhost:3000/method1 -r 50 -c 5
50....45....40....35....30....25....20....15....10....5....
Total time: 240.383527755737
Average time: 4.80767055511475

$ bench -u http://localhost:3000/method2 -r 50 -c 5
50....45....40....35....30....25....20....15....10....5....
Total time: 156.147093772888
Average time: 3.12294187545776

So it's obvious that method2 is better right? Well, not necessarily. While benchmarks only show averages, you'll need to pay attention to standard deviations. The bigger the standard deviation, the more runs you'll need to figure out the average load time, and the number of decimal points you can trust. That way, you can figure out whether the difference in load times is statistically significant or not.

That way, you can ascertain whether the optimization you made were worth the trouble or not. tip!

Use barriers to your advantage

I use to read iwillteachyoutoberich, as he had some useful tidbits, and I, like many twenty-somethings, usually worry about personal finances...But anyway, the one piece that I really like that I gleamed from him was his take on barriers.

I think the source of 95%+ of barriers to success is…ourselves. It’s not our lack of resources (money, education, etc). It’s not our competition. It’s usually just what’s in our own heads. Barriers are more than just excuses–they’re the things that make us not get anything done. And not only do we allow them to exist around us, we encourage them. There are active barriers and passive barriers, but the result is still the same: We don’t achieve what we want to.

He had another post where he turned it around and said that you can make barriers work to your advantage as well, not just in avoiding kooks, but in increasing your productivity.

Since I do web dev, the browser's up all the time, and it's really easy just to hit ctrl-t www.facebook.com. And then before you know it, a whole half hour's been wasted. It's even worse with proggit or hacker news. A couple days ago, there was a tip on 4 lines to increase your productivity (can't find it now) on reddit, and it was just lines in a /etc/hosts file. It reminded me of barriers, so I decided to try it out.

I set up my /etc/hosts file:

127.0.0.1       www.facebook.com
127.0.0.1       news.ycombinator.com
127.0.0.1       news.octoparts.com
127.0.0.1       programming.reddit.com

# if I'm really having problems concentrating:
127.0.0.1       www.gmail.com
127.0.0.1       mail.yahoo.com

And lo and behold, it actually worked. Just the extra step of having to type in a command and a password is enough to deter me from not working. I do still hit ctrl-t once in a while, but then I'm reminded that it's fruitless, and I might as well get back to work. My friend Ian closes everything but a max windowed emacs as his productivity trick.

Anyone got any others they fool themselves with to get crackin'?

Using anonymous functions inside functions

I was reading an article on Javascript and its use of first class functions. I'd quote it if I could find it again, but basically, it extolled the virtues of being able to create anonymous functions, blocks, and closures easily in Javascript. One of the things that it claimed was that creating local functions only used within a method makes the code much more readable. I was skeptical, but as I was refactoring this function, I thought I'd give it a shot even though I was coding in Ruby. Ruby also allows for the creation of first class functions.

It's just a helper function that generates a bookmark button--however, what gets generated depends on whether a user is logged in and whether a user had already bookmarked the page.

  def bookmark_button(page, user, indicator_id)
    if page.bookmarked_by? session[:user]
      "Bookmarked!"
    elsif page.done_by? session[:user]
      link_to_remote image_tag('heart_add.png', :height => 16, :width => 16) + " Bookmark again!", 
                               :url => { :controller => :bookmark_list, :action => :add, :page_id => page.id  }, 
                               :loading => "Element.toggle('#{indicator_id}')", 
                               :complete => "Element.toggle('#{indicator_id}')"
    else
      link_to_remote image_tag('heart_add.png', :height => 16, :width => 16) + " Bookmark!", 
                               :url => { :controller => :bookmark_list, :action => :add, :page_id => page.id  }, 
                               :loading => "Element.toggle('#{indicator_id}')", 
                               :complete => "Element.toggle('#{indicator_id}')"
    end
  end

Well, I thought it was pretty straightforward to read, though half of it was duplicated code. It wasn't very DRY. So instead of fudging around with another way to structure the control flow, I tried my hand at using blocks. I ended up with this:

  def bookmark_button(page, user, indicator_id)
    bookmark_link = Proc.new { |label| 
      link_to_remote "#{image_tag('heart_add.png', :height => 16, :width => 16)} #{label}", 
                     :url => { :controller => :bookmark_list, 
                               :action => :add, 
                               :page_id => page.id  }, 
                     :loading => "Element.toggle('#{indicator_id}')", 
                     :complete => "Element.toggle('#{indicator_id}')"
    }

    if page.bookmarked_by? session[:user]
      "Doing this"
    elsif page.done_by? session[:user]
      bookmark_link.call("Bookmark again!")
    else
      bookmark_link.call("Bookmark!")
    end
  end

As you can see, I put the link_to_remote() code into a block, since the only difference between the two is the label. In addition, it is possible for the block to use variables that are in this method, but outside the block, even if the execution is outside the scope of this function, if the block is ever passed outside of bookmark_button. I know in javascript, this causes memory leaks in IE. I haven't heard that it's a problem in Ruby yet.

But in this case, I'm just creating a function inside a method to make things more readable and cleaner. I think for the most part, it worked pretty well. As long as it's not overdone (notice I didn't create a proc for the labels), it should make for more readable code, and you don't pollute the class namespace with methods that are only used in this one method. I should get use to this. tip!

Parallel array processing with zip()

When I'm working in Ruby, it's a blast, but a lot of the concepts are borrowed from functional style programming, and I'm not sure what things are called. Often times, I end up writing the same boiler plate code over and over again, refactoring it into a function that I add to the standard library on my own, while knowing there's probably a built-in function to do that. It was like that with inject(). Today, I discovered zip().

I run into this particular problem when I want to line up arrays with one another, and perform an operation on the same corresponding element of each array--much like a parallel map function. For example, vector addition and multiplication is like this. When you add arrays, you take the the nth element from each vector and add them together.

Usually, I write something like this:

a,b = [1,2,3], [2,3,4]
class Array
  def parallel_map(b)
    result = []
    each_with_index do |e, i|
      result << yield e, b[i]
    end
  end
end

a.parallel_map(b) { |ea, eb| ea + eb }

Which is pretty ugly, as I shamefully admit. However, due to the post I last mentioned about Erlang, as well as this post on Ruby talk, I (finally) made the connection that there's such a function in ruby, and it's (also) called zip().

The solution then would look something like this:

a.zip(b).map { |i, j| i + j }

MUCH better. That means something like dot_product is a lot more elegant now.

def dot_prod(a, b)
  a.zip(b).map { |i, j| i + j }.inject { |t, e| t += e }
end

To be honest, I've read the reference API on Ruby's enumerable, array, and hash libraries before. However, at the time that I read zip(), I was thinking, "I'm not sure when I'll ever need to do that.", and just put it out of my mind. :P
tip!

Self-referential many-to-many join with extra data and non-standard foreign keys

Here's another gotcha that I ran into that's kind of an edge case in Rails. So I'm documenting it, so that the rest of you can go about your business of building great apps, instead of scratching your heads. So what was I doing? I wanted a self-referential join table with rich associations for an "acts_as_friendable" plugin I was writing.

I made table in database as follows:

  create_table "friendships", :force => true do |t|
    t.column "owner_id",  :integer, :null => false
    t.column "friend_id", :integer, :null => false
  end

In the model, put:

  class Friendship < ActiveRecord::Base
    belongs_to :owner, :class_name => "User", :foreign_key => :owner_id
    belongs_to :friend, :class_name => "User", :foreign_key => :friend_id
  end

Then in the table that you want to act as friendable, you put:

  class User < ActiveRecord::Base
   
    acts_as_friendable
 
  end

And that's it. you can now access friends() and friendships() of a person.

However, it doesn't work when you try to push the association through, like:

user = User.find(1)
friend = User.find(2)
user.friends << friend

It will fail complain about how "user_id" doesn't exist in any of the tables. I was scratching my head for a good 2 hours before I figured that it wasn't actually me this time. I think the << method doesn't correctly use the foreign keys correctly when they're non-standard like this. According to #6466 ([PATCH] fix for has_many :through push and delete with legacy/non-standard foreign_keys), this doesn't work, until a patch is written for it. I'm not as familiar with the Rails code base as I should be. This is probably a good chance to get started looking at it...unless someone else fixes it first...

As a workaround, I simply used the Friendship ActiveRecord object directly to create the association. I'll have to override the method in the plugin so that it allows correct use of << for my specific case. Tip!

Email attachments not downloading on Textdrive servers

This was one of those things that had me reeling in pain a month ago. I couldn't figure out what exactly was wrong...and I've run into this problem twice! The symptom was ActionMailer, which in turn is using Rails TMail extensions, didn't seem to be downloading attachment correctly on the server. It worked correctly on my development machine, but when I run it on the production server, it just didn't want to work. All attachments would be two bytes. I had suspected a host of other things, but I'll spare you the stupidity. It's a long chain from mail attachment to webpage, and it took a lot of work to narrow it down to Rail's TMail extensions.

It ends up that this is only an issue if base64.so is on the user's system. According to this two year old post on Textdrive, ActionMailer's TMail will choose between two implementations of base64, a C one or a Ruby one, based on the existence of the library base64.so

The problem is, the ruby version assumes that a string will return, and the C version assumes an array will return. And because of that, calling first() on a string only gives the first byte or two, as opposed to calling first on an array, which gives the first element (a string)

I hotfixed it, because I couldn't get a plugin to work and override the classes. I didn't spend too much time with it, so if anyone else wants to show me how to do the plugin for this simple fix, I'd be happy to learn.

In base64.rb in the rails directory (I froze my rails in my vendors directory) I changed the code to:

module TMail

  module Base64
    def rb_decode( str, strict = false )
      str.unpack('m').join
    end    
  end

end

And subsequently, in unquoter.rb

module Unquoter

  class << self
    def unquote_base64_and_convert_to(text, to, from)
      convert_to(Base64.decode(text), to, from)
    end    
  end

end

That should fix your problems for now. I was using rails 1.2.0 and it still hasn't been fixed. I know someone else submitted a patch for it already (Rails bug #7861). Tip!