为什么当生产中仅需要 mysql2 时会出现此错误?

Question

我的 gemfile 有这样一行：

gem 'mysql2', group: :production

但是当我从命令行运行命令时出现此错误：rails r "puts Rails.env"

/Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activerecord-4.2.6/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec': Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord)
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activerecord-4.2.6/lib/active_record/connection_adapters/connection_specification.rb:174:in `spec'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activerecord-4.2.6/lib/active_record/connection_handling.rb:50:in `establish_connection'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activerecord-4.2.6/lib/active_record/railtie.rb:120:in `block (2 levels) in <class:Railtie>'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:28:in `block in on_load'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:27:in `each'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:27:in `on_load'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/activerecord-4.2.6/lib/active_record/railtie.rb:116:in `block in <class:Railtie>'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `instance_exec'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `run'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/railties-4.2.6/lib/rails/initializable.rb:55:in `block in run_initializers'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:226:in `block in tsort_each'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:348:in `block (2 levels) in each_strongly_connected_component'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:429:in `each_strongly_connected_component_from'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:347:in `block in each_strongly_connected_component'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `each'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `call'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `each_strongly_connected_component'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:224:in `tsort_each'
from /Users/cgunnels/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:203:in `tsort_each'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/railties-4.2.6/lib/rails/initializable.rb:54:in `run_initializers'
from /Users/cgunnels/.rvm/gems/ruby-2.2.2@global/gems/railties-4.2.6/lib/rails/application.rb:352:in `initialize!'
...
rest of stack trace

附带说明：我一直无法弄清楚为什么mysql2不会安装。我已经尝试了每个堆栈溢出搜索的几个修复程序，但没有骰子。

更新： 我没有提到，但我想在开发环境中。

Answer 1

当你运行rails r而不告诉哪个环境时，Rails将使用development环境作为回退。

您有三种选择：

1. 生产环境中的启动导轨

   bundle exec rails runner -e production "puts Rails.env"
   

   或

通过

2. 从Gemfile的gem 'mysql2'行中删除, group: :production，在所有环境中安装mysql2gem。

   或

3. 更新config/database.yml以在开发环境中使用sqlite3而不是mysql2。

Answer 2

您可能会收到错误，因为当您不在生产环境中时，没有数据库驱动程序。