Archive for February 2011
Controller instance variables in Rails partials
A model value in a Rails partial can be a controller @instance variable or a local variable passed in by the calling template. What should it be?
Some model values must vary within a single page, so can’t be instance variables. Even when instance variables can be used, they still smell bad to the careful coder, because they have broad scope — they’re visible to every template that makes up the page. However, the controlled scope of a local comes with a cost: the template that sets it must know about it, which means more coupling between the partial and the calling template. If the partial’s locals change, so must the calling template, and perhaps its caller and its caller. For a widely-used partial, this is a lot of work. With instance variables, the caller knows nothing, and the partial can change without ripples.
So, when can you take advantage of the convenience and reduced coupling of passing model values to a partial via instance variables?
Test patterns: red-green-refactor vs. frequent committing
Agile and lean principles lead to committing frequently, each commit potentially deployable to production. I’ve always been one to save my work often, and I commit often, not just whenever I finish an entire task, but whenever I’ve written enough code to justify running my tests, I do so, and they pass. This always seems like the right thing to do: it’s usually easy to break down big tasks into small, committable, deployable bits, and I can almost always point to the value in each commit, whether an implemented test, a refactoring or just a spelling fix. But I recently found myself in a situation where I realized that committing a (correct) test and its implementation that I’d just written would introduce a bug.
latin1, utf8, Rails 2.3.9 and mysql2
GWW‘s database.yml (which originated under Rails 1.something) has never specified an encoding. We seem to have gotten away with it because mysql defaults to latin1, our database is latin1 (probably because mysql defaults to it) and the mysql gem was happy with that default. It was clear that non-ASCII characters were being handled correctly, because when using GWW one often sees Flickr usernames that contain them.
Discussions of encodings often include a statement like “start using UTF-8 now, because more and more software will assume it in the future”. They were right, and the future is now. Working towards upgrading to Rails 3, I recently updated GWW to Rails 2.3.10 and replaced the mysql gem with the mysql2 gem (which Rails 2.3.9 and later require). I’m pretty sure this is when GWW began dropping the ball on non-ASCII characters, displaying them all as question marks. I didn’t actually roll back the upgrade to prove it, and I don’t know whether it’s Rails 2.3.9/10 or mysql2. I was more interested in fixing the problem quickly — which, fortunately, it could be.
Test patterns: One test per path
I’ve seen many test suites which were much less thought through and much less well factored than the code they tested. But that’s not right: Tests drive the code, so tests are at least as important as code. You should care about the quality of your tests just as much as you do the quality of your code, and refactor your tests just as vigorously as you do your code. Here, then, are some thoughts on one aspect of good test design: the One test per path pattern.
Filtering spam with GMail and SPF, episode II: “Attack of the Spam”
A year ago I described how I sent my email through GMail to filter spam, and how I remailed my email instead of forwarding it to satisfy SPF. But there was an onion in the ointment. Because I was remailing my email, GMail learned that mail from my mail server often contained spam, which GMail recognized as spam from other sources. (“Often” here means as often as spamassassin, which I was still running on my mail server, let spam slip through.) GMail frequently guessed that real mail was spam, and although I could correct it sender by sender, I had to watch my GMail spam folder constantly for mail from real human beings whom GMail hadn’t seen before. That was almost as much work as deleting the actual spam myself in the first place. What’s more, although I’m not aware that this ever happened, for all I know GMail’s low opinion of my mail server might make it think that mail that originated on my server was spam.
Fortunately, there was an easy solution: stop passing the buck.
self.welcome_back
After posting once and then going dark more than a year ago, I’m now on sabbatical and am again of a mind to write down things related to what I’m working on. Right now that’s Guess Where Watcher, a Ruby on Rails application used for scoring the Guess Where San Francisco Flickr game. Let’s see where this goes in a month or two.
Dave Schweisguth in a Bottle 