我正在尝试从rails 2.3升级到rails 3，并完成了rake rails:upgrade:check的事项清单，但是，当我尝试启动rails控制台时，我遇到以下错误，当我尝试并访问任何表：
irb(main):010:0> Game.all
ActiveRecord::ConnectionNotEstablished: ActiveRecord::ConnectionNotEstablished
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/connection_adapters/abstract/connection_pool.rb:317:in `retrieve_connection'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/connection_adapters/abstract/connection_specification.rb:97:in `retrieve_connection'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/connection_adapters/abstract/connection_specification.rb:89:in `connection'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/base.rb:602:in `quoted_table_name'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/relation/query_methods.rb:275:in `build_select'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/relation/query_methods.rb:189:in `build_arel'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/relation/query_methods.rb:149:in `arel'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/relation.rb:64:in `to_a'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/relation/finder_methods.rb:143:in `all'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activerecord-3.0.20/lib/active_record/base.rb:444:in `all'
from (irb):10
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.0.20/lib/rails/commands/console.rb:44:in `start'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.0.20/lib/rails/commands/console.rb:8:in `start'
from /Users/ttt/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.0.20/lib/rails/commands.rb:23:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
我正在使用mysql，升级到mysql2 gem，我的gem文件看起来像：
gem "rails", "3.0.20"
gem 'mysql2', '~> 0.2.17'
我还将database.yml更新为
development_default: &development_default
adapter: mysql2
encoding: utf8
reconnect: false
pool: 5
socket: /tmp/mysql.sock
development:
<<: *development_default
database: some_database
username: some_user
password: some_password
host: some.domain.com
port: 4000
我可以切换回我的rails 2分支并运行代码，所以它肯定与我的升级代码有关。问题是什么或下一步在哪里？