我已经运行了 gem install mysql2，将 lib 文件添加到 bin 文件夹中，mysql2 在 gem 文件中。怎么了？

# MySQL.  Versions 4.1 and 5.0 are recommended.
# 
# Install the MYSQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   http://dev.mysql.com/doc/refman/5.0/en/old-client.html
development:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: dealers
  pool: 5
  username: fredric
  password: test
  host: localhost

Mysql2::Error (Access denied for user 'fredric'@'localhost' (using password: YES)):
  mysql2-0.3.11-x86 (mingw32) lib/mysql2/client.rb:44:in `connect'
  mysql2-0.3.11-x86 (mingw32) lib/mysql2/client.rb:44:in `initialize'
  activerecord (3.2.1) lib/active_record/connection_adapters/mysql2_adapter.rb:16:in `new'
  activerecord (3.2.1) lib/active_record/connection_adapters/mysql2_adapter.rb:16:in `mysql2_connection'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:277:in `new_connection'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:287:in `checkout_new_connection'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:235:in `block (2 levels) in checkout'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:230:in `loop'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:230:in `block in checkout'
  C:/Ruby193/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:229:in `checkout'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:95:in `connection'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:374:in `retrieve_connection'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_specification.rb:168:in `retrieve_connection'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_specification.rb:142:in `connection'
  activerecord (3.2.1) lib/active_record/query_cache.rb:67:in `rescue in call'
  activerecord (3.2.1) lib/active_record/query_cache.rb:61:in `call'
  activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:443:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
  activesupport (3.2.1) lib/active_support/callbacks.rb:405:in `_run__874471498__call__280582312__callbacks'
  activesupport (3.2.1) lib/active_support/callbacks.rb:405:in `__run_callback'
  activesupport (3.2.1) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
  activesupport (3.2.1) lib/active_support/callbacks.rb:81:in `run_callbacks'
  actionpack (3.2.1) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/reloader.rb:65:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
  railties (3.2.1) lib/rails/rack/logger.rb:26:in `call_app'
  railties (3.2.1) lib/rails/rack/logger.rb:16:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/request_id.rb:22:in `call'
  rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
  rack (1.4.1) lib/rack/runtime.rb:17:in `call'
  activesupport (3.2.1) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
  rack (1.4.1) lib/rack/lock.rb:15:in `call'
  actionpack (3.2.1) lib/action_dispatch/middleware/static.rb:53:in `call'
  railties (3.2.1) lib/rails/engine.rb:479:in `call'
  railties (3.2.1) lib/rails/application.rb:220:in `call'
  rack (1.4.1) lib/rack/content_length.rb:14:in `call'
  railties (3.2.1) lib/rails/rack/log_tailer.rb:14:in `call'
  rack (1.4.1) lib/rack/handler/webrick.rb:59:in `service'
  C:/Ruby193/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
  C:/Ruby193/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
  C:/Ruby193/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'


  Rendered C:/Ruby193/lib/ruby/gems/1.9.1/gems/actionpack-3.2.1/lib/action_dispatch/middleware/templates/rescues/_trace.erb (3.0ms)
  Rendered C:/Ruby193/lib/ruby/gems/1.9.1/gems/actionpack-3.2.1/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (39.0ms)
  Rendered C:/Ruby193/lib/ruby/gems/1.9.1/gems/actionpack-3.2.1/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within rescues/layout (108.0ms)
[2012-02-05 20:30:54] WARN  Could not determine content-length of response body. Set content-length of the response or set Response#chunked = true

最佳答案

由于您的 PRIVILEGES 设置，这看起来像是访问控制问题。请记住，localhost 是一种特殊情况，在授予权限时未被 % 涵盖，因为它将通过本地 UNIX 套接字而不是端口 3306 TCP 套接字进行连接。

您应该使用 mysql 命令行工具检查您是否可以从运行该应用程序的同一台计算机进行连接:

mysql --user=frederic --password=test dealers

此时您应该得到与 Mysql2 驱动程序相同的错误。

通常这是通过更新您的授权来解决的:

GRANT ALL PRIVILEGES ON dealers.* to `frederic`@`localhost` IDENTIFIED BY 'test'

关于mysql - 无法在 Ruby on Rails 中连接到 MySQL，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/9152282/