Rails using mysql2 instead of sqlite3 - ruby-on-rails

Question

I have the following configuration:
linux ubuntu 11.04
rails 3.0.9
ruby 1.9.2p290
mysql2 (0.2.7)
I have created first my project using "rails new"
then I have modified the Gemfile to use mysql2 version 0.2.7 (I have read that later versions are working with rails 3.1 only)
Then I changed the file database.yml to use mysql2 instead of sqlite3
But now I'm getting error ActiveRecord::ConnectionNotEstablished when I try to connect to a Controller. Here are the full logs:
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/connection_pool.rb:317:in `retrieve_connection'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/connection_specification.rb:97:in `retrieve_connection'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/connection_specification.rb:89:in `connection'
activerecord (3.0.9) lib/active_record/query_cache.rb:12:in `cache'
activerecord (3.0.9) lib/active_record/query_cache.rb:31:in `call'
activerecord (3.0.9) lib/active_record/connection_adapters/abstract/connection_pool.rb:354:in `call'
actionpack (3.0.9) lib/action_dispatch/middleware/callbacks.rb:46:in `call'
activesupport (3.0.9) lib/active_support/callbacks.rb:416:in `_run_call_callbacks'
actionpack (3.0.9) lib/action_dispatch/middleware/callbacks.rb:44:in `call'
rack (1.2.3) lib/rack/sendfile.rb:107:in `call'
actionpack (3.0.9) lib/action_dispatch/middleware/remote_ip.rb:48:in `call'
actionpack (3.0.9) lib/action_dispatch/middleware/show_exceptions.rb:47:in `call'
railties (3.0.9) lib/rails/rack/logger.rb:13:in `call'
rack (1.2.3) lib/rack/runtime.rb:17:in `call'
activesupport (3.0.9) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.2.3) lib/rack/lock.rb:11:in `call'
rack (1.2.3) lib/rack/lock.rb:11:in `synchronize'
rack (1.2.3) lib/rack/lock.rb:11:in `call'
actionpack (3.0.9) lib/action_dispatch/middleware/static.rb:30:in `call'
railties (3.0.9) lib/rails/application.rb:168:in `call'
railties (3.0.9) lib/rails/application.rb:77:in `send'
railties (3.0.9) lib/rails/application.rb:77:in `method_missing'
railties (3.0.9) lib/rails/rack/log_tailer.rb:14:in `call'
rack (1.2.3) lib/rack/content_length.rb:13:in `call'
rack (1.2.3) lib/rack/handler/webrick.rb:52:in `service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:104:in `service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:65:in `run'
/usr/lib/ruby/1.8/webrick/server.rb:173:in `start_thread'
/usr/lib/ruby/1.8/webrick/server.rb:162:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:162:in `start_thread'
/usr/lib/ruby/1.8/webrick/server.rb:95:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:92:in `each'
/usr/lib/ruby/1.8/webrick/server.rb:92:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:23:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:82:in `start'
rack (1.2.3) lib/rack/handler/webrick.rb:13:in `run'
rack (1.2.3) lib/rack/server.rb:217:in `start'
railties (3.0.9) lib/rails/commands/server.rb:65:in `start'
railties (3.0.9) lib/rails/commands.rb:30
railties (3.0.9) lib/rails/commands.rb:27:in `tap'
railties (3.0.9) lib/rails/commands.rb:27
script/rails:6:in `require'
script/rails:6
PS: I tried almost all solutions provided in this website, but I still have the same issue.

Answer 1

I ended by recreating a new project with the command
rails new -d mysql
And now the pages are retrieved without any problem!
I tried to compare the automatic database.yml file and the manual one, the only diffrence I have noticed was on the user used for mysql database. in the new one the username: root is used.
I came back to the old project and I changed to username/password with root ones I now it is working!!!

Answer 2

I would guess that your database.yml file is incorrect. It should look something like this:
development:
adapter: mysql2
host: localhost
username: root
password: xxxx
database: xxxx
If that doesn't work, try changing localhost to 127.0.0.1