Pivotal Blabs

At Pivotal, we host tech talks for our and guest developers. You can now subscribe to these video and audio tech talks on iTunes!

Just search for "Pivotal Labs" in iTunes, or click on the 'Video' or 'Audio' buttons on our Talks page. The current playlist includes:

• Scrum - Christian Sepulveda gives an overview of the Scrum development process as it applies to software.
• HAML - Felix Mario and Aaron Peckham talk about HAML.
• Vertebra - Ezra Zygmuntowicz talks about Vertebra, the distributed cloud application programming platform Engine Yard is building.
• Fire Eagle - Seth and Blaine talk about Fire Eagle, a location-awareness provider for online applications. Fire Eagle is a Yahoo! venture and gives applications and websites user-configurable information about the user's location.
• New Relic - Lewis Cirne demos New Relic's real-time Rails performance monitoring and analysis tool.
• Devver - Benk Brinkerhoff and Dan Mayer talk about Devver
• Rubini.us - Evan Phoenix answers questions about Rubinius, a Ruby virtual machine and compiler written as much as possible in Ruby.

One interesting thing this morning:

The RailsEnvy blog had a segment talking about a team of engineers building a series of social network plugins using the Pivotal Lab's technology: Dessert.

Those of us used to Desert (one 's') were wondering what Dessert might be, leading to this quip from Adam:

"Dessert is Desert with a lot of syntactic sugar."

Ask For Help

Once again, a project is asking for everyone's favorite IE 6 .PNG alpha transparency fixes -- more rounded corners! Examples include the CSS Behavior code, using .PNGs or .GIFs with on/off transparency, regulating IE 6 to the square Web 1.0 world, and even using on/off transparency and just knocking a pixel or two off of corners for a "good enough" rounded look.

What are your favorite IE 6 rounded-corner and/or alpha-transparency fixes?

Helps

What is capistrano multistage?

• A plugin that allows you to store environment-specific variables in different files, and specify a default environment
• It's been on tracker for a while and seems to be stable
• Other options are just specifying your environment-specific variables within separate tasks - keeping everything in one file

Ask for Help

One of our clients is looking for high-quality third-party chat services/libraries.

Interesting Things

10.5.5 and screen sharing

The Mac screen sharing application includes a host of interesting power features. Unfortunately, upgrading to Mac 10.5.5 causes these features to go away. Workarounds at this point are to store off the application and re-install it. Or to pay $300 for the official solution. Whichever.

Additional routing-related helper methods

It can be useful to create helper methods designed to extend the routing helpers offered by routes.rb.. power "_path" and "_url" methods. While the easy solution is to define these methods in your view helper layer (the most common client of these methods), a more complete solution is to use a pattern like this:

in routes.rb:

          ActionController::Routing::Routes.draw do |map|
               ... normal routes ...
          end

          ActionController::Routing::Helpers.module_eval do
             def additional_method_name
              ...
             end
          end

Any methods added to ActionController::Routing::Helpers will be available in all of the same places that named routes are defined - controllers, views, and ActionController::UrlWriter includers.

Testing Flash in Selenium

Most Flash applications render an inline image in addition to the Flash itself. This image updates as the Flash updates, and appears to be used for caching purposes.

When you're test-driving, you can make assertions about when this inline image updates to test Flash behavior. The image is binary, so it's hard to make assertions about exactly what has changed.. but it's a start.

Interesting Things

When you specify a gem from a custom source, and it has dependencies on a separate source, you need to list both sources in geminstaller.yml.

This comes up when you are installing a gem from github and that gem depends on other gems from rubyforge. You can specify multiple sources by adding more --source attributes.

Ask for Help

When using a namespaced controller, it's hard to get url_for to work with it. Why is that?

• The controller option for url_for attempts to apply the namespace of whatever controller context it's inside. So if you have an Admin::MyController class, here's what you would need to do for url_fors to this controller:

  • from within an Admin controller class: :controller => "my"

  • from outside an Admin controller class: :controller => "admin/my"

  • for a partial that is used all over the app: :controller => "/admin/my" seems safest

• Most of us now avoid using url_for-style hashes for our links and URL references. Named routes are a lot more dependable.

• It is possible to generate a namespaced URL from a model reference, if you are careful.

  • This approach assumes that your controller class names correspond to your model class names.

  • If your model is @model, and your controller is Admin::ModelsController, you can use a helper like the following:

     form_for [:admin, @model] do |f| ... end
    

  • This approach can limit your design, if you rely too heavily on this convention.

Interesting Things

How to read your class's name

While working with the UltraSphinx plugin, Davis and Brandon learned that Class.name didn't always give them the right results. Some of their classes had a class method override what Class.name returned.

Class.class_name came closer, but returns the base class for STI (single table inheritance) classes.

Class.to_s was their most reliable option.

Testing your app on both MySQL and PostGRES

David S. is working on a plugin that allows you to test your environment on multiple databases. Since we're starting to have more projects using PostGRES, we're uncovering situations where some of our common code makes too many assumptions about running on MySQL.

Slutty namespaces

A couple of projects ran into mysterious issues where some of their namespaced controller classes would not load when run from rake.

The culprit was that their namespace module names were the same name as their app models. The lesson - never have a module with the same name as one of your other unrelated classes. (No, I'm not talking about inner classes, which can be fine).

A prime example of this is an Admin::* namespace coexisting with an Admin model. This will cause strange problems depending on what order the classes are loaded. One recommendation is to pluralize your namespaces. In this case, your namespace would be Admins::*.

Another suggestion would be to use an extended noun form for your namespace (Administration::*). Whatever convention you use, stick to it and avoid name collisions.

Ask for Help

David and Jonathan are having trouble with testing namespaced controllers using RSpec. They have two controllers, Admin::MyController and SuperUser::MyController, and the RSpec tests appear to be finding the wrong controller.

Their short-term solution is to put a manual require in the spec that was getting confused.

UPDATE - The issue turns out to be a naming conflict. The app has a model named SuperUser, and the existence of this model can cause class loading to be confused for SuperUser::* controllers. In Socialitis, our standard is to use plural names for controller namespace names, to prevent this sort of confusion.

Interesting Things

Steve has learned that, in general, it's a good idea to avoid using offsets when manipulating large quantities of data in MySQL. Luckily, some of MySQL's quirks help with this:

• MySQL sorts indexes. The primary key is the main index that it sorts.
• Any select without an explicit order clause will pick an index, then return data in sorted order by that index. Again, usually you'll see the primary key first.

• You can take advantage of this behavior to paginate through a large dataset where the order doesn't really matter. The following statements perform better than your typical LIMIT/OFFSET clause:

  SELECT * FROM big_table WHERE id > 1 LIMIT 1000
  SELECT * FROM big_table WHERE id > 1000 LIMIT 1000
  SELECT * FROM big_table WHERE id > 2000 LIMIT 1000
  

• acts_as_solr uses this technique for reindexing.

• Also, inserting a record in the middle of an id 'hole' is not a very good idea in MySQL, because the database then puts a great deal of work into reordering all of the later records.

Here's a link to a related blog post: http://weblog.jamisbuck.org/2007/4/6/faking-cursors-in-activerecord

Interesting Things

• When using standard rails partials you always have a local variable named _counter. In previous versions of rails, the partial_counter variable was set to 0 when you passed an object, and set to 1 for the first item in a collection. Now it appears to start at 0 whether you pass an object or a collection.

• Brian Takita has begun work on chaining doubles in RR

• Our site has a number of buttons which are: (a) really links which look like buttons instead of links, (b) ajaxy actions, which typically cause an edit box to appear, or (c) form submissions. This item is especially about (a) and perhaps (b). Right now we have what is a glorified styled a tag, as described here. We've been having trouble getting that to work right (in particular, the height seems off by one pixel in mysterious circumstances). Probably the easiest solution is the rails button_to helper, which makes a form with one button in it (and method=get). This loses some desirable behaviors of the a tag (such as being able to control click or menu-click to open in a new tab), but certainly solves the rendering hassles.