我一直无法让mysql2适配器使用最新版本的rails。我刚刚创建了一个新项目。在我的gemfile中添加了以下内容：
gem 'mysql2', '< 0.3.7'
然后当然跑了：
bundle install
我还修改了我的database.yml文件：
development:
adapter: mysql2
encoding: utf8
database: blog_development
username: root
password: *********
socket: /tmp/mysql.sock
test:
adapter: mysql2
encoding: utf8
database: blog_test
username: root
password: ********
socket: /tmp/mysql.sock
production:
adapter: mysql2
encoding: utf8
database: blog_production
username: root
password: *********
socket: /tmp/mysql.sock
因此，当我尝试运行rake db：create时，以下是输出。
$ rake db:create --trace
** Invoke db:create (first_time)
** Invoke db:load_config (first_time)
** Invoke rails_env (first_time)
** Execute rails_env
** Execute db:load_config
** Execute db:create
rake aborted!
Please install the mysql2 adapter: `gem install activerecord-mysql2-adapter` (can't activate mysql2 (~> 0.3.10), already activated mysql2-0.3.6. Make sure all dependencies are added to Gemfile.)
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/bundler-1.1.3/lib/bundler/rubygems_integration.rb:157:in `block in replace_gem'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/connection_adapters/mysql2_adapter.rb:3:in `<top (required)>'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activesupport-3.2.2/lib/active_support/dependencies.rb:251:in `require'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activesupport-3.2.2/lib/active_support/dependencies.rb:251:in `block in require'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activesupport-3.2.2/lib/active_support/dependencies.rb:236:in `load_dependency'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activesupport-3.2.2/lib/active_support/dependencies.rb:251:in `require'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/connection_adapters/abstract/connection_specification.rb:48:in `resolve_hash_connection'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/connection_adapters/abstract/connection_specification.rb:27:in `spec'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/connection_adapters/abstract/connection_specification.rb:127:in `establish_connection'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/railties/databases.rake:67:in `create_database'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/railties/databases.rake:40:in `block (3 levels) in <top (required)>'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/railties/databases.rake:40:in `each'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.2/lib/active_record/railties/databases.rake:40:in `block (2 levels) in <top (required)>'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:205:in `call'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:205:in `block in execute'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:200:in `each'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:200:in `execute'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:158:in `block in invoke_with_call_chain'
/Users/teddyknox/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:151:in `invoke_with_call_chain'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/task.rb:144:in `invoke'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:116:in `invoke_task'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:94:in `block (2 levels) in top_level'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:94:in `each'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:94:in `block in top_level'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:133:in `standard_exception_handling'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:88:in `top_level'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:66:in `block in run'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:133:in `standard_exception_handling'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/lib/rake/application.rb:63:in `run'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/gems/rake-0.9.2.2/bin/rake:33:in `<top (required)>'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/bin/rake:19:in `load'
/Users/teddyknox/.rvm/gems/ruby-1.9.3-p125/bin/rake:19:in `<main>'
Tasks: TOP => db:create
告诉我要安装：
gem install activerecord-mysql2-adapter
但这个宝石不存在。我很困惑。我尝试了很多不同版本的mysql2，但似乎都没有。有什么想法吗？
答案 0 :(得分：11)
在gemfile中使用以下内容似乎有效：
gem "mysql2", "~> 0.3.11"
答案 1 :(得分：3)
看起来你的宝石需要mysql2 ~> 0.3.10（意思是＆gt; = 0.3.10＆amp;＆amp;＆lt; 0.4），而你需要它＆lt; 0.3.7。尝试删除版本上的约束并再次bundle install？