rake db:create 的问题答案

【问题标题】：Issue with rake db:createrake db:create 的问题
【发布时间】：2015-12-11 15:13:36
【问题描述】：

我认为这是一个常见问题，但我已经尝试了我在其他几篇文章中读到的内容，但我遇到了同样的命运。

我使用的是 rbenv，因为这是我首先遇到的。

rake db:create
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_adapters/connection_specification.rb:174:in `spec'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/connection_handling.rb:50:in `establish_connection'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:8:in `establish_connection'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/mysql_database_tasks.rb:15:in `create'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:93:in `create'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:107:in `block in create_current'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:275:in `block in each_current_configuration'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:274:in `each'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:274:in `each_current_configuration'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/tasks/database_tasks.rb:106:in `create_current'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/railties/databases.rake:17:in `block (2 levels) in <top (required)>'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:240:in `call'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:240:in `block in execute'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:235:in `each'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:235:in `execute'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:179:in `block in invoke_with_call_chain'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:172:in `invoke_with_call_chain'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/task.rb:165:in `invoke'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:150:in `invoke_task'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:106:in `block (2 levels) in top_level'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:106:in `each'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:106:in `block in top_level'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:115:in `run_with_threads'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:100:in `top_level'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:78:in `block in run'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:176:in `standard_exception_handling'
    /Users/cmunger/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rake/application.rb:75:in `run'
    /Users/cmunger/.rbenv/versions/2.2.3/bin/rake:33:in `<main>'
    Couldn't create database for {"adapter"=>"mysql2", "encoding"=>"utf8", "pool"=>5, "username"=>"blogApp", "password"=>"*****", "socket"=>"/tmp/mysql.sock", "database"=>"blog_test"}
    rake aborted!
    Gem::LoadError: 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).

Gem::LoadError: can't activate mysql2 (~> 0.3.13), already activated mysql2-0.4.2. Make sure all dependencies are added to Gemfile

我的版本和捆绑安装。 mysql2在那里...

cmunger@Claytons-Mac:~/Desktop/Devlopment/blog$ rbenv versions
  system
* 2.2.3 (set by RBENV_VERSION environment variable)
cmunger@Claytons-Mac:~/Desktop/Devlopment/blog$ bundle install
Using actionmailer 4.2.4
Using actionpack 4.2.4
Using actionview 4.2.4
Using activejob 4.2.4
Using activemodel 4.2.4
Using activerecord 4.2.4
Using activesupport 4.2.4
Using arel 6.0.3
Using binding_of_caller 0.7.2
Using builder 3.2.2
Using bundler 1.10.6
Using byebug 8.2.1
Using coffee-rails 4.1.0
Using coffee-script 2.4.1
Using coffee-script-source 1.10.0
Using concurrent-ruby 1.0.0
Using debug_inspector 0.0.2
Using erubis 2.7.0
Using execjs 2.6.0
Using globalid 0.3.6
Using i18n 0.7.0
Using jbuilder 2.3.2
Using jquery-rails 4.0.5
Using json 1.8.3
Using loofah 2.0.3
Using mail 2.6.3
Using mime-types 2.99
Using mini_portile2 2.0.0
Using minitest 5.8.3
Using multi_json 1.11.2
Using mysql2 0.4.2
Using nokogiri 1.6.7
Using rack 1.6.4
Using rack-test 0.6.3
Using rails 4.2.4
Using rails-deprecated_sanitizer 1.0.3
Using rails-dom-testing 1.0.7
Using rails-html-sanitizer 1.0.2
Using railties 4.2.4
Using rake 10.4.2
Using rdoc 4.2.0
Using sass 3.4.20
Using sass-rails 5.0.4
Using sdoc 0.4.1
Using spring 1.5.0
Using sprockets 3.5.2
Using sprockets-rails 2.3.3
Using thor 0.19.1
Using thread_safe 0.3.5
Using tilt 2.0.1
Using turbolinks 2.5.3
Using tzinfo 1.2.2
Using uglifier 2.7.2
Using web-console 2.2.1
Bundle complete! 12 Gemfile dependencies, 54 gems now installed.
Use `bundle show [gemname]` to see where a bundled gem is installed.

我认为下面的错误可能是我问题的根源：

Gem::LoadError: can't activate mysql2 (~> 0.3.13), already activated mysql2-0.4.2. Make sure all dependencies are added to Gemfile

我尝试将其改回，但我得到：

gem 'mysql2', '~> 0.4.2'
ERROR:  While executing gem ... (Gem::CommandLineError)
    Unknown command mysql2,

我可以提供的任何进一步信息请询问。我在使用 rbenv 安装时关注了一个 wiki，这就是我所在的位置。

【问题讨论】：

标签： ruby-on-rails ruby rubygems rbenv

【解决方案1】：

除非您运行的是 Rails 4.2.5 或更高版本，否则您需要将以下内容放入您的 Gemfile：

gem 'mysql2', '~> 0.3.10'

来源：mysql gem compatibility listing

【讨论】：

【解决方案2】：

您需要将bundle exec 添加到您的命令中，否则您将在全局gemset 上执行它：

bin/rake db:create

作为替代方案，您可以使用 binstubs：

bundle exec rake db:create

【讨论】：

您只需将gem mysql2 添加到Gemfile 并运行bundle install
@YuryLebedev，我认为您在答案中颠倒了代码 sn-ps 的顺序
@benjamin 您认为 binstubs 是首选方式吗？我也这么认为，但想让答案更接近最初的问题
@YuryLebedev，它在我的 gemfile 中，但仍然出现上述错误。
@YuryLebedev，这不是我的意思。您的回答读起来就像您的意思是“bundle exec ...”是一个 binstub。

【解决方案3】：

对于 Rails 4.2.5 或更高版本，请使用此

gem 'mysql2', '~> 0.3.18'

然后

bundle install

【讨论】：

【解决方案4】：

仅在您的 gemfile 中使用（目前）

gem mysql2

在你的命令行中，运行

$ gem install -v '0.3.13'
$ bundle exec bundle update
$ bundle exec bundle install

【讨论】：

【解决方案5】：

对尝试了以上所有方法但仍然面临同样问题的人提供一点额外建议。

我最初尝试过

安装 rbenv
将rbenv global 和rbenv local 设置为所需的版本
在我的项目中创建一个.ruby-version 文件并设置为所需的版本 4、将建议的rbenv条目放在我的.bash_profile中
用rbenv version 测试了我的设置，得到了我的预期
并尝试了该线程上建议的其他一些方法

没有任何效果。

最后，经过几个小时的撞击和尝试不同的事情，最终解决问题的是重新启动。所以只是一个提示：如果所有这些建议都失败了，不要像我一样浪费时间：重新启动。

我在运行bundle install 时第一次遇到这个问题。上面列出的 rbenv 步骤与重新启动相结合，解决了这个问题。然后问题又出现在rails db:create 命令上，即使bundle install 仍在同一个bash 会话中工作！我再次检查了所有内容，最终解决的问题是重新启动。

【讨论】：