title: undefined method `visitor' for Rails 3 db:migrate
body: <p>I am experiencing an exception while doing a database migration in Rails 3.</p>
  
  <pre><code>undefined method `visitor' for #&lt;ActiveRecord::ConnectionAdapters::Mysql2Adapter:0x00000103dea3d8&gt;
  </code></pre>
  
  <hr>
  
  <p><strong>Edit</strong></p>
  
  <p>Please check the solution <a href="https://stackoverflow.com/questions/7001479/undefined-method-visitor-for-rails-3-dbmigrate/7010671#7010671">here</a>.</p>
  
  <hr>
  
  <p>No occurrence for the string <code>visitor</code> inside my project so I am puzzled.</p>
  
  <p>Here is the full dump:</p>
  
  <pre><code>$ rake db:migrate --trace
  ** Invoke db:migrate (first_time)
  ** Invoke environment (first_time)
  ** Execute environment
  ** Invoke db:load_config (first_time)
  ** Invoke rails_env (first_time)
  ** Execute rails_env
  ** Execute db:load_config
  ** Execute db:migrate
  rake aborted!
  undefined method `visitor' for #&lt;ActiveRecord::ConnectionAdapters::Mysql2Adapter:0x00000103dea3d8&gt;
  .rvm/gems/ruby-1.9.2-p180/gems/arel-2.1.5/lib/arel/tree_manager.rb:19:in `visitor'
  .rvm/gems/ruby-1.9.2-p180/gems/arel-2.1.5/lib/arel/tree_manager.rb:23:in `to_sql'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:562:in `get_all_versions'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:708:in `migrated'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:635:in `current_version'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:652:in `block in migrate'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:652:in `each'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:652:in `detect'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:652:in `migrate'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:545:in `up'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/migration.rb:526:in `migrate'
  .rvm/gems/ruby-1.9.2-p180/gems/activerecord-3.1.0.rc5/lib/active_record/railties/databases.rake:161:in `block (2 levels) in &lt;top (required)&gt;'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:205:in `call'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:205:in `block in execute'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:200:in `each'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:200:in `execute'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:158:in `block in invoke_with_call_chain'
  .rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:151:in `invoke_with_call_chain'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/task.rb:144:in `invoke'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:112:in `invoke_task'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:90:in `block (2 levels) in top_level'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:90:in `each'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:90:in `block in top_level'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:129:in `standard_exception_handling'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:84:in `top_level'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:62:in `block in run'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:129:in `standard_exception_handling'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/lib/rake/application.rb:59:in `run'
  .rvm/gems/ruby-1.9.2-p180/gems/rake-0.9.2/bin/rake:32:in `&lt;top (required)&gt;'
  .rvm/gems/ruby-1.9.2-p180/bin/rake:19:in `load'
  .rvm/gems/ruby-1.9.2-p180/bin/rake:19:in `&lt;main&gt;'
  Tasks: TOP =&gt; db:migrate
  </code></pre>