group :development,:test do
   gem 'sqlite3'
end
group :production do
  gem 'MysqL'
end

开发机器没有安装MysqL,这就是为什么我只在生产组中列出了MysqL.但是当我尝试在开发机器上运行Rails时,我得到：

$> RAILS_ENV=development ./script/rails 
Could not find gem 'MysqL (>= 0,runtime)' in any of the gem sources listed in your Gemfile.

显然,我可以通过安装MysqL解决这个问题,但是我想知道正确的解决方案,而不是安装不需要的软件.