Ruby使用MySQL问题记录
1.使用gem安装mysql2的时候提示以下错误extconf.rb:2:in `require': no such file to load -- mkmf (LoadError) from extconf.rb:2
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.8 extconf.rb
extconf.rb:2:in `require': no such file to load -- mkmf (LoadError)
from extconf.rb:2
原因：缺少mkmf，mkmf.rb is part of the ruby1.8-dev package。
解决办法：sudo apt-get install ruby1.8-dev
2.WARNING: This version of mysql2 (0.3.2) doesn't ship with the ActiveRecord adapter bundled anymore as it's now part of Rails 3.1
WARNING: Please use the 0.2.x releases if you plan on using it in Rails <= 3.0.x
原因：rails版本小于3.1，mysql2版本大于0.3，造成版本不兼容；
解决办法：在Gemfile里面把mysql2的版本调低一点设成gem 'mysql2', '< 0.3'就可以了，或者直接gem install mysql2 -v 0.2.7安装一个确切的版本，再在gemfile中将mysql2设成该版本；或者把rails升级到3.1以上版本，该方法未验证。
3.Installing mysql2 (0.3.6) D:/develop/Ruby192/lib/ruby/site_ruby/1.9.1/rubygems/defaults/operating_system.rb:9:in `block in <t
op (required)>': The 'mysql2' native gem requires installed build tools. (Gem::InstallError)
原因：缺少devkit，无法安装mysql2；
解决办法：去'http://rubyinstaller.org/downloads 下载devkit，然后按照http://github.com/oneclick/rubyinstaller/wiki/Development-Kit 的说明安装测试，再执行即可。
4.安装mysql2时报ERROR:Failed to build gem native extension.，具体如下：
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
google后发现很多人在安装的时候把mysql自身的参数带上就可以装成功，比如带--with-mysql-lib=${mysqlLibPath}或--with-mysql-dir=${mysqlDir}或--with-mysql-config=${mysqlConfigPath}。都有试过还是一样，最后从apt中装了个mysql的开发包libmysqlclient-dev，才从gem上将mysql安装成功。