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The Application Controller in Rails 2.3 has been renamed to application_controller.rb, whereas previously it was application.rb. If you don’t fix it, calling any controller will return this cryptic error.

 NameError in MyController#search
uninitialized constant ApplicationController

After trying to fix this by checking out an older revision, reconfiguring Mongrel/Apache and generally turning things on & off, I discovered the fix.

rake rails:update

That was all it needed! The Rake task will rename the file accordingly, and instructs you to update your source code repository. I guess it serves me right for not using the same Rails version on my development and production servers. On development I use 2.2.2 and on production I upgraded to 2.3. A point release can be a big difference!

Hope this saves you some desperately late nights.

This entry was posted on Friday, June 5th, 2009 at 12:48 am and is filed under development, ruby on rails. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.