Ruby giving "NoMethodError: undefined method `[]' for nil:NilClass" with Sinatra

Question

I am total newbie to Ruby and Sinatra and I am trying to learn them.

So this is my ruby code (File: ruby_test2.rb)

#!/usr/bin/ruby
require 'rubygems'

class LearnRuby

  def initalize
    @listen = Hash.new { |hash, key| hash[key] = []; }
  end

  def fill_listen(uid, mid)
    @listen[uid]<<=mid
    "In fill_listen #{@listen}\n"
  end

end

And this is my Sinatra code (file: sinatra_test2.rb)

require 'sinatra'
require './ruby_test2'

if __FILE__ == $0
  lr = LearnRuby.new
end

post '/listen' do
  lr.fill_listen params[:uid] , params[:mid]
end

An this is how I am running it.

ruby sinatra_test2.rb <-- Starts the server

curl --data "uid=u1&mid=m312" http://localhost:4567/listen <-- Curl command for post request

When I execute the above I get this error (on server and client(curl) side)

localhost - - [22/Mar/2014:22:54:19 IST] "POST /listen HTTP/1.1" 500 3770
- -> /listen
NoMethodError - undefined method `[]' for nil:NilClass:
    <path>/ruby_test2.rb:11:in `fill_listen'
    sinatra_test2.rb:9:in `block in <main>'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1593:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1593:in `block in compile!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:957:in `[]'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:957:in `block (3 levels) in route!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:976:in `route_eval'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:957:in `block (2 levels) in route!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:997:in `block in process_route'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:995:in `catch'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:995:in `process_route'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:955:in `block in route!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:954:in `each'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:954:in `route!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1067:in `block in dispatch!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1049:in `block in invoke'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1049:in `catch'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1049:in `invoke'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1064:in `dispatch!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:889:in `block in call!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1049:in `block in invoke'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1049:in `catch'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1049:in `invoke'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:889:in `call!'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:877:in `call'
    /var/lib/gems/1.9.1/gems/rack-protection-1.5.2/lib/rack/protection/xss_header.rb:18:in `call'
    /var/lib/gems/1.9.1/gems/rack-protection-1.5.2/lib/rack/protection/path_traversal.rb:16:in `call'
    /var/lib/gems/1.9.1/gems/rack-protection-1.5.2/lib/rack/protection/json_csrf.rb:18:in `call'
    /var/lib/gems/1.9.1/gems/rack-protection-1.5.2/lib/rack/protection/base.rb:50:in `call'
    /var/lib/gems/1.9.1/gems/rack-protection-1.5.2/lib/rack/protection/base.rb:50:in `call'
    /var/lib/gems/1.9.1/gems/rack-protection-1.5.2/lib/rack/protection/frame_options.rb:31:in `call'
    /var/lib/gems/1.9.1/gems/rack-1.5.2/lib/rack/logger.rb:15:in `call'
    /var/lib/gems/1.9.1/gems/rack-1.5.2/lib/rack/commonlogger.rb:33:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:217:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:210:in `call'
    /var/lib/gems/1.9.1/gems/rack-1.5.2/lib/rack/head.rb:11:in `call'
    /var/lib/gems/1.9.1/gems/rack-1.5.2/lib/rack/methodoverride.rb:21:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/show_exceptions.rb:21:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:180:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:2004:in `call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1469:in `block in call'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1778:in `synchronize'
    /var/lib/gems/1.9.1/gems/sinatra-1.4.4/lib/sinatra/base.rb:1469:in `call'
    /var/lib/gems/1.9.1/gems/rack-1.5.2/lib/rack/handler/webrick.rb:60:in `service'
    /usr/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
    /usr/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
    /usr/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'
localhost - - [22/Mar/2014:22:54:51 IST] "POST /listen HTTP/1.1" 500 3770

I may be missing out on something small but I need help as I am just starting to learn these technologies.

Thanks in advance.

Answer 1

Here is the working example for you, the @listen was nil, because you misspelled initalize -> initialize

require 'sinatra'

class LearnRuby
  def initialize
    @listen = {}
  end

  def fill_listen(uid, mid)
    @listen[uid] = mid
    "In fill_listen #{ @listen }\n"
  end
end

post '/listen' do
  lr = LearnRuby.new
  lr.fill_listen(params[:uid], params[:mid])
end

Answer 2

replace @listen[uid]<<=mid with @listen[uid] = mid

Also, in case you only require initialize to create an empty hash then you can replace @listen = Hash.new { |hash, key| hash[key] = []; } with @listen = {}