has_many :through

By way of the obligatory sorry-I-haven't-blogged-much-lately apologette, I should say that life has been busy this summer. The second biggest deal for me was, get this, moving to New York City. Yes, I know I just moved to a new place in San Francisco, and no, I haven't given up on my favorite city. It's a temporary move and I should be back in SF by the end of the year. What happened is that Pivotal Labs has opened an office in Manhattan, and I've come out to work on client projects and help get the office going. The takeaway on that is that Pivotal Labs is available for projects in New York, and we're also looking to hire top-notch Rails developers to work with us here.

The word I have to pick to describe New York is vital. That's true of the city in general, but from what I've heard it's also true of the Ruby development community. I am looking forward to getting to hang with folks here and see what I can learn from the other coast. There's a lot of Ruby developer events around here. I'm going to start with the nyc.rb hackfest tomorrow.

While I'm out here on the East Coast, I'm going to hit up some conferences. In November I'll be attending RubyConf 2008 in Orlando. Then later that month I'll be at the Voices That Matter: Professional Ruby Conference, giving a talk entitled "Ruby: Fragile or Agile?"

In the mean time, where's the best pizza in New York?

I recently packed up everything I own and moved. I'd lived in my old place for about nine years and I have the packrat gene on both sides of the family tree, so I had a lot of crap to sort through to figure out what to move and what to trash, as well as which box what should go in. Now that I'm here in the new place, I've had to sort through the remaining stuff to figure out where it all goes. So you might appreciate that sorting has been on my mind a lot lately. (See? It's a topical tie-in. I don't do those often, so I hope it wasn't too awkward.)

I've also been working on an application that does a lot of sorting to prioritize tasks in a workflow. These items often need to be sorted based on multiple criteria, such as how long an application has been waiting for approval, how many times a customer has been called recently, etc. We also have to sort names that have anywhere from two to four components (Hispanic names can have both paternal and maternal names instead of just a surname).

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I'm not sure where I first heard that you could do a recursive lamdba in Ruby, but it's been simmering on the back burner of my brain for a while. I've just never had a reason to use one, until now...

I wanted to process the Rails request params, which is a hash of strings and hashes of strings and hashes of strings and hashes... you get the idea. The need was to strip all the accent marks from user input throughout the application. Here's what I came up with:

class ApplicationController < ActionController::Base
  before_filter :strip_accents

  protected
  def strip_accents
    thunk = lambda do |key,value|
      case value
        when String then value.remove_accents!
        when Hash   then value.each(&thunk)
      end
    end
    params.each(&thunk)
  end
end

That's all completely clear, right? The filter enumerates the top-level hash using the &/to_proc operator to coerce the lambda to a block for the #each method. #each passes the key and value to the lambda, which either removes the accents from a string, or recursively enumerates the contents of a nested hash.

I think it's totally cool that you can do this in Ruby. Everyone thinks that Ruby is just an object-oriented language, but I like to think of it as the love-child of Smalltalk and LISP (with Miss Perl as the nanny).

A couple of months ago I ran into a weird issue in my current Rails project that made no sense at all. All we did was add a lock_version field to a model to enable optimistic locking and suddenly things started breaking in a big way. After a bit of digging we found it was because ActiveRecord wasn't properly quoting a table name when updating a record with optimistic locking. I submitted a patch for that issue (so it's fixed in Rails 2.1), but lately I've seen a few similar bugs having to do with table name quoting in various circumstances. The amusing thing to me is that all of these bugs have one thing in common: they were uncovered by creating a model named Reference.

At first I thought this was a pretty big coincidence, but after just a moment's thought it seemed pretty obvious. ActiveRecord pluralizes model names to form conventional table names, and references is a reserved keyword in MYSQL. I guess Reference is a word that makes a good model name, especially if you're building a big data graph and can't think of a more specific relationship name, and it's about the only noun that pluralizes into a reserved keyword that anyone would ever use. In our case, we could have done a rename refactoring to change the model class name to CharacterReference. Instead we used an override and changed the table name to t_references, since that seemed like the least effort for a temporary workaround until the fix got released with Rails 2.1.

All these various issues with table name quoting are indeed bugs in ActiveRecord and should be reported and fixed. (There's also a major reworking of the internals of ActiveRecord in progress that should deal with virtually all of these issues in one fell swoop.) But in the mean time, you might want to avoid using model names that generate SQL reserved words, or just override the table name to something else.

I'm finally recovered from RailsConf. Wish I could say the same thing for my car, which seems to have gone into a major funk from being ignored so much. Anyway, it's been cool reading all the aftermath posts and seeing people's thoughts and analysis of the conf. MagLev seems to be getting a lot of the attention, and I'm eager to see how things develop with it.

If you missed me at the conf, or saw me but just can't get enough of me, here's some links to a couple interviews people did with me there.

Gregg Pollack did some very nice video spots with many of the conf speakers. His RailsConf in 36 Minutes video is great. If you don't want to watch the whole thing (but why wouldn't you?), he posted the interview with me separately too.

Fabio Akita did some great podcast interviews at RailsConf. You can grab mine directly too.

As I said in my chat with Fabio, the next thing I'm going to do is release the Teldra code on GitHub. Stay tuned, it shouldn't be too long now.

Happy Friday!