Ruby

This one stumped me for a while today. I had an application to deploy which worked fine in development. Deploying to production led to this error:

/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.0.5/lib/active_support/dependencies.rb:249:in `load_missing_constant': Expected /myapp/releases/20090617160914/app/models/widget.rb to define Widget (LoadError)

Googling that error turned up lots of pages for Rails 1.2.x and issues with underscores in names. None of it applied. Widget was definitely being defined in widget.rb. Following the stack trace it appeared that the error was thrown in the Ultrasphinx plugin. After trying a lot of other things, I decided to comment out the Ultrasphinx code in the model and retry. The error changed to this, which was helpful:

Errno::EACCES: Permission denied - /myapp/releases/20090617160914/public/widget/myfile

This model was also using the file_column plugin, and the underlying error was just a permissions problem in the file attachment target directory. I fixed the permissions and put the Ultrasphinx code back in the model, and all was happy. If only that permissions error had shown up first!

After much frustration, I found a way to get the Ruby mysql Gem installed and talking to my MySQL server on MAMP. Credit goes largely to "Hootbah" who followed a similar path to get MAMP talking to Perl's MySQL library. Here's the steps I followed for MAMP 1.7.2:
Success!

I recently needed to run through one data file, pull a number, and look that number up in several other data files. So in Ruby, I first opened the initial file, pulled the number, and then opened the other files, iterating through every line until I found a match, then call break to move on. This worked, but it was sort of slow.

It occurred to me that I could use grep to see if the number was in the other files. So I had to figure out how to call it from Ruby. Here's what I came up with:

The speed improvement depends on how many searches you're doing and the size of the files you're searching, but in a quick test the grep calls were 5x faster.

Shoulda is a handy plugin for Rails (now a Gem), which makes writing tests easier. It's worth checking out. Shoulda has been very helpful with a big Rails project I've been working on all summer, and I submitted a couple small contributions and bug fixes. I was surprised to see my name mentioned in the newest release, but I appreciate it, and it was fun helping out!

Here's a gotcha that I came across today: don't define a constant as something in one Rails rake task file, and then define the same constant as something different in another file, because the last constant will supercede them all:


I guess this happens because Rake is loading all of the task files before running the requested task. There's probably a way to namespace the constant, but I need to do more research on that. In the meantime I'll use different constant names!

I was initially disappointed when it was announced that Ruby on Rails was moving its version control system from Subversion to Git. There's enough to keep up with in Rails that I didn't relish having to keep up with this as well. It wasn't so much that Rails was moving, but related code began to move too, so we're currently in this limbo where many plugins have both git and soon-to-be-deprecated SVN repositories, and it's just another detail to keep track of. Hopefully there will be tools to sort all this out soon.

I like my SVN GUI tools, but it turns out that git works pretty well on Windows under Cygwin, if you can live with the command line. It's certainly sufficient for cloning plugin repositories.

I could take or leave git by itself, but I love GitHub. They make it so easy to fork an existing project, make your own changes to it, and share it back with the world. Your changes can easily be pulled back into the original projects, too. I've been able to make a couple of small contributions to shoulda and acts_as_xapian.

So git is fun after all, and I'm looking forward to using it more; especially when the GUI tools show up.

Today I came across a PNG file that had been uploaded from a browser with a .JPG extension and image/jpeg MIME type. It's too bad that MIME types are apparently unreliable when it comes to file uploads. I went looking for a way to determine the file type by actually reading the file. This is probably a solved problem, but I was unsuccessful Googling for the answer. I came up with the following Ruby method which decides the image file type using up to the first 10 bytes:


This works well on a small set of test files (400+ from a browser temp files directory). Let me know if there's a case where this code doesn't work, or if there's a better solution in general.

I've made a code contribution to Ruby on Rails. It was minor, but I'm glad I could help. See ticket 10435 and changeset 8386.

Supposed to get some rain today...keeping my fingers crossed.

Update 2007-12-17: Looks like my patch made it into Rails 2.0.2. And we did get that rain, but more would be good.

Update 2008-03-17: I managed to get another small patch committed. Go open source!

I'm fairly new to the Ruby language and the Ruby on Rails framework, but it worked nicely for quickly building my website BirdSite.

I was using validates_inclusion_of fairly regularly to make sure the data in my models was valid. But then, watching the development log, I noticed extra SQL queries being made when I accessed my main model. It seems that validates_inclusion_of was forcing the model to make queries to the related models even when I didn't need data from them.

Some Googling led to a blog post that did the validation a different way. It worked well, until I added the code to a new model today and it broke. The code was translating the model field name into a string from which to call the model itself. But the code assumed that the model would be a single word. I added a change to strip the spaces out, and it worked again.

I contacted the company that hosts the blog and they confirmed that it was a problem, and they didn't know of a nicer Ruby way to correct it short of dropping the spaces with search/replace. They updated their code.

I'm glad I could help out. It really works better than the standard validates_inclusion_of.

I wanted to add a search feature to my Ruby on Rails application BirdSite. There is a plugin called "acts_as_ferret" which allows Rails applications to use the Ferret search engine (based on Lucene).

Using this tutorial, I was able to get search up an running. It worked great on my development system. But there was a warning that you needed to run the indexer using a DRb server instead of directly from the Rails app. This is because the index cannot handle multiple processes writing to it simultaneously. (I also ran into this problem using PHP with another engine called Xapian).

I was hoping my new site was low traffic enough to avoid problems. Since I'm hosting it on a shared server, I can't run a DRb server there anyway. But I got my first indexing exceptions less than 24 hours after I loaded my stuff onto the live server.

So I decided to try periodic indexing by a cron job. This would allow me to update the index once an hour, from a single process. The downside is that the search index is only updated hourly, but I decided I could live with that.

The first step is telling your Rails app to not index the content when updating. My model already had a before_save method, so I added this code:


Then I had to create a rake task which would build the index:


This task is simplified: I'm telling it to rebuild the entire index each hour. I'm guessing when my dataset gets big enough, this will be really slow. In that case I'll need to track all the model instances that got updated in the past hour and just index those.

Finally, I needed a cron job to run the rake task, making sure to set the environment to "production":


So far this is working well, and I haven't received any indexing exceptions since.