Interesting Things

• Be careful when extending classes from structs. Their superclasses are essentially anonymous classes, so reopening them can be difficult. If you attempt to reopen them by extending them from "the same" struct, it will actually be a different anonymous class.

• Ever had an STI model but wanted the views and controllers to pretend like it all extended the base class? You can have rails change the params[] namespace that it uses like so:

  form_for :user, @admin_user, :url => user_path(@admin_user)

Or you can be super-cool and use polymorphic routes:

form_for @admin_user.becomes(User)

The becomes method is part of ActiveRecord, and it actually creates a 2nd copy of the object with the same attributes and a different class (shallow copy). Due to this implementation, it has limitations so use it carefully.

• Upgrading to rails 2.3.3 breaks HopToad. This is related to filter_parameter_logging, and it's technically rails' fault. It has been fixed in 2.3.3 stable (which I assume will be released as 2.3.4). You can also fix it yourself with a one-line-patch. Personally, I'd wait to upgrade till 2.3.4 comes out.

Interesting Things

• One of our projects is using mechanical turk to match and normalize their ugly data. After building some automatic matching with little success, the group is simply using the template web interface. The task can be trivially decomposed into tiny tasks, and accuracy does not need to be 100% perfect, so it's a great fit. They only spent a few hours and have results already!

When creating associations to classes that use Single Table Inheritance (STI), rails is smarter about the hierarchy than I would have expected. A call to find on a base class yields a query that does not filter on type. But what about a call to find on a subclass? Instead of making a single filter on type, rails finds all the subclasses of that subclass and creates an "OR" expression in the "WHERE" clause.

Generated SQL respects class heirarchy

# ActiveRecord::Base < User < Admin < SuperAdmin 
something.admin    # has_one :admin

Generates the following SQL:

# SELECT * FROM users WHERE (type = 'Admin' OR type = 'SuperAdmin')

When it doesn't work

Since it relies on the class hierarchy, the query is only accurate if every subclass has been loaded. If class preloading is off, for example, very weird things can happen. The query will depend non-deterministically on which subclasses have been loaded.

Ask for Help

"How do I redefine a CSS class in javascript"

You can create a new <style> element and append it to the head. This should probably be avoided if you can help it.

If you simply want to toggle between 2 states, consider putting both sets of rules in the CSS and toggling a class on the body or other container.

*"Should I use BOSH for XMPP on the iPhone?"

Probably not. If you have a long-running low latency XMPP connection, you'll probably want to use a socket from the CFNetwork package. That's the most we know about iPhone development right now.

Interesting Things

• New tracker updates with better burndown charting!