Wednesday, August 26, 2009

Pair programming really works!

I've known this in the past and I had another "Aha!" moment the other day: pair programming (or debugging in this case) is great!

I've had a problem for the past week or so in one of my applications. I'm in the middle of a big upgrade (from Rails 1.3.6 to Rails 2.3.2 and lots of other associated changes), when I hit a hard stop; my screen wasn't getting updated correctly after an Ajax call.

I struggled with this for quite some time and then today called Allan Miller, a good friend of mine over to help me debug it. He sat down, I described he problem and demonstrated it. He said "Well, let's take a look and make sure that you're actually getting an XHR request." so we fired up FireBug and entered a couple of trials: the POST request was properly executed and my application did see it as an XHR request. Everything's working as exepcted so far, but no errors and no screen refresh.

Since he had been focusing on the Ajax call, I decided to show him the code on the page, and used FireBug's feature to "click an element to inspect" and pointed out the code [line breaks inserted for readability; this is all one line of code]:
<a class="ltr-locate" onclick="new Ajax.Updater('asset-content', '/asset/get_assets?ltr=F',
{asynchronous:false, evalScripts:true, parameters:'authenticity_token=
' + encodeURIComponent('xxx')}); return false;" href="/asset/get_assets" align="right">F</a>

"See" I said. "There's the AjaxUpdater call to update the... ... that's it!" The first field in the AjaxUpdater call signifies the named area on the page that will be updated as a result of the call. In this case 'asset-content'. "I'll bet that they changed the name in the intervening releases" I said.

Sure enough, that was the case: the name name is 'as_asset-content' and updating the link_to_remote call solved the problem. What a relief!

I've got 3 take-aways from this:
  1. Two heads are at least 10 times better than 1, if you compare 50 total minutes of work (25 minutes times 2 heads) with at least 10 hours of work with my one head. There's just something magical about having to REALLY explain your code to an outside observer that makes you think thru things much more carefully. It's making the thinking process external, rather than internal where your hidden assumptions come into play without your even knowing it.
  2. The AjaxUpdater call gives NO ERROR if the named area doesn't exist; it just quietly closes up shop, assuming that you knew what you were doing.
  3. I was reminded how great FireBug is for this kind of thing. Quick and easy to see that the Ajax call was firing with the right information so that we could move on to the next question.
Extrapolating that out, I would imagine that -- had there beeen two folks in the seat from the beginning -- this whole thing wouldn't have taken so long... and the code would probably be better for it.

Reminds me of the old "Double your pleasure..." chewing gum ad, only in this case it's really true.

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