29 Jan / 2010
Variables you shouldn’t use in a rails controller
I ran into this issue and spent an hour debugging this. Writing
it here, so it might help some one else.
Lets create a simple RAILS project
rails hello cd hello ./script/generate controller hello
Add a simple index method
app/controller/hello_controller.rb
class HelloController < ApplicationController def index end end
app/views/hello/index.html.erb
<html> <title> </title> <body> <h1>Hello world</h1> <%= link_to 'index', :controller => 'hello', :action => 'index' %> </body> </html>
In your browser go to url http://localhost:3000/hello
. You wil get the simple greeting
All is fine.
Now lets add an instance variable in the controller
app/controller/hello_controller.rb
class HelloController < ApplicationController
def index
@url = "http://www.sujee.net"
end
end
Do a reload….
Awww….
undefined method `rewrite’ for “http://sujee.net”:String
So our innocent little variable caused this!!
What is going on here? Turned out we inadvertantly over-wrote an
internal variable Rails uses; that happens to be @url.
If we change this variable to say ‘@myurl’ things start to work again.
How can we find out what variables are being used? Lets update
our controller
app/controller/hello_controller.rb
class HelloController < ApplicationController
def index
puts self.instance_variables
end
end
Reload the page. And look at the console where ‘script/server’ is
running.
=> Booting WEBrick => Rails 2.3.4 application starting on http://0.0.0.0:3000 => Call with -d to detach => Ctrl-C to shutdown server [2010-01-28 23:58:10] INFO WEBrick 1.3.1 [2010-01-28 23:58:10] INFO ruby 1.8.7 (2008-08-11) [universal-darwin10.0] [2010-01-28 23:58:10] INFO WEBrick::HTTPServer#start: pid=94840 port=3000 @_session @_params @url @performed_redirect @request_origin @_request @_headers @performed_render @action_name @template @_response @before_filter_chain_aborted Processing HelloController#index (for 127.0.0.1 at 2010-01-28 23:58:14) [GET] Rendering hello/index Completed in 79ms (View: 77, DB: 0) | 200 OK [http://localhost/hello]
We over-wrote @url and caused the problem.
There you go, don’t name your variables as one of these:
- @_session
- @_params
- @url
- @performed_redirect
- @request_origin
- @_request
- @_headers
- @performed_render
- @action_name
- @template
- @_response
- @before_filter_chain_aborted
Thanks a bunch to my collegue Go Kojima for helping me
debug this issue.
Sujee is a founder, principal at Elephant Scale where he provides consulting and training on Big Data technologies
2 Comments:
By Walter Sheridan 10 Dec 2012
What ist for instance the difference between @_params and params?
When you try to merge a hash with params, it says params is nil. I just don’t get the difference…
By Pristi 02 Aug 2015
I would recommend one thin prsecos per prsecosor/core. Because there is only one underlying thread, you can only peg one core at a time. Basically think of thin as Mongrel, except it can handle many concurrent requests safely.Fibers are only in 1.9. There has been some work done to port them to 1.8 but I strongly urge just upgrading. You also gain a nice improvement in Ruby execution speed.