Ruby on Rails mysql2 adapter problem

I have installed ruby and rails and my application gives me an error when I am trying to run

rake db:migrate

this is the result of the command rake db:migrate --trace

** Execute db:migrate
rake aborted!
!!! Missing the mysql2 gem. Add it to your Gemfile: gem 'mysql2'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/mysql_adapter.rb:22:in `rescue in mysql_connection'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/mysql_adapter.rb:19:in `mysql_connection'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:229:in `new_connection'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:237:in `checkout_new_connection'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:191:in `开发者_JAVA技巧block (2 levels) in checkout'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:187:in `loop'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:187:in `block in checkout'
/usr/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:186:in `checkout'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:94:in `connection'
/usr/lib/ruby/gems/1.9.1/gems/ar-octopus-0.3.4/lib/octopus/proxy.rb:83:in `select_connection'
/usr/lib/ruby/gems/1.9.1/gems/ar-octopus-0.3.4/lib/octopus/proxy.rb:177:in `send_queries_to_selected_slave'
/usr/lib/ruby/gems/1.9.1/gems/ar-octopus-0.3.4/lib/octopus/proxy.rb:140:in `method_missing'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:454:in `get_all_versions'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:583:in `migrated'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:492:in `current_version'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:509:in `block in migrate'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:509:in `each'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:509:in `detect'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:509:in `migrate'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:433:in `up'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/migration.rb:415:in `migrate'
/usr/lib/ruby/gems/1.9.1/gems/activerecord-3.0.6/lib/active_record/railties/databases.rake:142:in `block (2 levels) in <top (required)>'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:636:in `call'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:636:in `block in execute'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:631:in `each'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:597:in `block in invoke_with_call_chain'
/usr/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2029:in `block (2 levels) in top_level'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2029:in `block in top_level'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2001:in `block in run'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/usr/lib/ruby/gems/1.9.1/gems/rake-0.8.7/bin/rake:31:in `<top (required)>'
/usr/bin/rake:19:in `load'
/usr/bin/rake:19:in `<main>'
confiz@confiz-desktop:~/mango_apps/rails_app_sms$ .
bash: .: filename argument required
.: usage: . filename [arguments]

I have already mentioned gem in my gemfile and already executed bundle install.

My database.yml file already has the correct adapter i.e. adapter: mysql2

Please help me resolve this problem.

I find the same problem if I use mysql2 v 0.2.19b4 in my Gemfile. If I use the latest mysql2 this conflicts with rails 3.0.17 which is dictated by Hobo (which generated my Gemfile). The warning I get from that is:

This version of mysql2 (0.3.11) doesn't ship with the ActiveRecord adapter bundled anymore as it's now part of Rails 3.1. Please use the 0.2.x releases if you plan on using it in Rails <= 3.0.x

Going back to mysql2 v 0.2.x The original load error comes because the rails mysql_adapter calls require 'mysql' not require 'mysql2'.

The solution is to use gem 'mysql' not gem 'mysql2' in the Gemfile

In my case bundler users gem mysql v 2.8.1 and everything works fine.