Pivotal Blabs

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?

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

• 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.

Interesting Things

• Rspec - stubbing a class method

In Rspec you can stub a class method in a module using Module::Class:Stubs('method') similar to Mocha syntax stub! does not work for Module::Class:method in rspec

• Rspec - running test in order

If someone knows of a way to run describes in order in rspec test, please let me know

Ask for Help

"Finder conditions in rails?"

    find(:all, :conditions => 'flag is null')  where flag is boolean

This would work in tests but not in development mode. They tried changing it to

    find(:all, :conditions => 'flag != 1')  where flag is boolean

and this would work in dev mode but not in test.

Try having boolean values in database as not null and never pass null to boolean. Make sure fixtures and development data have similar data sets.

"Selenium tests failing to load associations"

Check if you RAILS_ENV is set to test while running Selenium. There has been some cases of weird rails behavior running tests when RAILS_ENV is set to development

Interesting Things

• One of the teams was trying to reopen the Time class to make to_date public. Another pivot noticed that there is no built in to_date in Time class in ruby. ActiveSupport has a to_date method on Time class that is public. The most interesting one is that there is a private to_date that is added to Time class when you include Yaml.

• We have git brown bag today on how to use git with the Pivotal Process.

Other stuff

• We are looking for one more unix system administrator preferably with scalability experience to help with our infrastructure. The job description is here. Well there are obvious benefits and then there is also free breakfast :)

• What's the best way to import a million records into a postgres database via ActiveRecord (which is needed to implement some application-specific logic)? We anticipate waiting a second (or so) between inserts to avoid slowing down the production database (which is under load, almost entirely reads). If there is any ActiveRecord feature which helps batch together inserts, noone knew about it. As for generally how long this will take (estimates range from 9 to 27 hours), and what the load on the production database will be, we planned on answering that with a trial run of a small number of these records.

• We're thinking of having capistrano deploy to two demo servers, one particularly aimed at showing to prospective users of our application, and the other mostly for story acceptance. The former would be hosted at a hosting company; the latter an internally run machine. Several people reported they have done this on their projects, and the problems were minor, mostly having to do with whether the deployed location (/u/apps/whatever or some such) is different on the two machines (the solution would be to use the capistrano variables, but tracking down all the places that need to do that could be an issue).

• Erector tip of the day: in a Rails project, you can put a file (named edit.rb or edit.html.rb) in your view directory, and Rails/Erector will find the template implicitly (as it would for ERB, HAML, etc). It is not necessary to explicitly call render from your controller method.