title: ruby datamapper will not load
body: <p>I was trying to learn about the Sinatra ruby framework by following this tutorial:</p>
  
  <p><a href="http://net.tutsplus.com/tutorials/ruby/singing-with-sinatra-the-recall-app-2/" rel="noreferrer">http://net.tutsplus.com/tutorials/ruby/singing-with-sinatra-the-recall-app-2/</a></p>
  
  <p>however, after running the gem install and writing a simple sinatra server in test.rb like so:</p>
  
  <pre><code>require 'sinatra'
  require 'datamapper'
  
  get '/' do 
    "Hello, World!"
  end
  </code></pre>
  
  <p>but when I run the command <code>ruby test.rb</code>, I get the following error:</p>
  
  <pre><code>/usr/local/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': no such file to load -- datamapper (LoadError)
      from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
      from datamapper_test.rb:2:in `&lt;main&gt;'
  glenn@ubuntu:~/Dropbox/Repositories/sandbox/sinatra$ ruby datamapper_test.rb 
  /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': no such file to load -- datamapper (LoadError)
      from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
      from test.rb:3:in `&lt;main&gt;'
  </code></pre>
  
  <p>it seems as though it cannot find the datamapper gem. how can I fix this?</p>
  
  <p><strong>EDIT</strong>: using ruby 1.9.2 </p>
  
  <p><strong>EDIT (again)</strong>: (parital) output from <code>gem list</code>:</p>
  
  <pre><code>data_mapper (1.2.0)
  data_objects (0.10.8)
  datamapper (1.2.0)
  devise (1.4.5)
  directory_watcher (1.4.0)
  dm-aggregates (1.2.0)
  dm-constraints (1.2.0)
  dm-core (1.2.0)
  dm-do-adapter (1.2.0)
  dm-migrations (1.2.0)
  dm-serializer (1.2.1)
  dm-sqlite-adapter (1.2.0)
  d    m-timestamps (1.2.0)
  dm-transactions (1.2.0)
  dm-types (1.2.1)
  dm-validations (1.2.0)
  do_sqlite3 (0.10.8)
  sinatra (1.3.2, 1.2.6)
  sqlite3 (1.3.5, 1.3.4)
  sqlite3-ruby (1.3.3)
  </code></pre>