軌控制檯--sandbox邁克爾·哈特爾的軌道教程第三版不知道這是如何工作

Question

我使用有一個問題與Ruby on Rails的：

rails console --sandbox 

所以在邁克爾·哈特爾的軌道教程第3版，我們正在使用此，我當我有時候使用它，並且一切順利，然後出現錯誤，並且從字面上看，整個測試環境變得無用，因爲它不會響應我的命令。例如，我將鍵入：

2.1.1 :025 > user.first 

，或者是工作，應該是工作，而是得到任何其他命令：

NoMethodError: undefined method `first' for #<User:0x007fede35e3188> 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activemodel-4.2.0.beta2/lib/active_model/attribute_methods.rb:435:in `method_missing'  from (irb):25 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2 gems/railties-4.2.0.beta2/lib/rails/commands/console.rb:110:in `start' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2 gems/railties-4.2.0.beta2/lib/rails/commands/console.rb:9:in `start' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/railties-4.2.0.beta2/lib/rails/commands/commands_tasks.rb:68:in `console' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/railties-4.2.0.beta2/lib/rails/commands/commands_tasks.rb:39:in `run_command!' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/railties-4.2.0.beta2/lib/rails/commands.rb:17:in `<top (required)>' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:248:in `require' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:248:in `block in require' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:233:in `load_dependency' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:248:in `require' 
    from /Users/andrewkim/workspace2/sample_app/bin/rails:8:in `<top (required)>' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:242:in `load' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:242:in `block in load' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:233:in `load_dependency' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:242:in `load' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/commands/rails.rb:6:in `call' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/command_wrapper.rb:38:in `call' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:180:in `block in serve' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:153:in `fork' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:153:in `serve' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:128:in `block in run' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:122:in `loop' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:122:in `run' 
    from /Users/andrewkim/.rvm/gems/ruby-2.1.1@railstutorial_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application/boot.rb:18:in `<top (required)>' 
    from /Users/andrewkim/.rvm/rubies/ruby-2.1.1/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require' 
    from /Users/andrewkim/.rvm/rubies/ruby-2.1.1/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require' 
    from -e:1:in `<main>'2.1.1 :026 > 

突然什麼，我在終端上鍵入將帶着這樣的錯誤，我不知道怎麼去無需退出「rails console --sandbox」。有沒有辦法？

Answer 1

for example, I will type:

2.1.1 :025 > user.first 

or any other command that was working and should be working

該命令不應該工作，它不起作用。您遇到錯誤是因爲在教程中有一個User實例，它表示表中的一行，例如

user = User.new(name: "Joe", email: "joe@yahoo.com") 

沒有名爲first()的方法。相反，用戶實例具有以下方法：

id() 
name() 
email() 
created_at() 
updated_at() 

然而，可以使用類名稱（或型號名稱）來搜索表格，例如，

user1 = User.first. #User is the name of the class/model 

至於這樣的：

and I don't know how to go back

回去呢？什麼也沒有變。在錯誤發生之前，您輸入到控制檯的所有變量仍然存在。這裏是一個軌道控制檯的例子：

$ rails console --sandbox 
Loading development environment in sandbox (Rails 4.0.8) 
Any modifications you make will be rolled back on exit 
2.0.0-p481 :001 > x = 10 
=> 10 

2.0.0-p481 :002 > user = User.find_by(email: "example@railstutorial.org") 
    User Load (4.0ms) SELECT "users".* FROM "users" WHERE "users"."email" = 'example@railstutorial.org' LIMIT 1 
=> #<User id: 2, name: "Example User", email: "example@railstutorial.org", created_at: "2014-10-02 01:39:04", updated_at: "2014-10-02 01:39:04", password_digest: "$2a$10$VNzivk5opu1AC5DOM467dO2JaTg3c3JC9OAXR0AqvEi0..."> 

2.0.0-p481 :003 > user.first 
NoMethodError: undefined method `first' for #<User:0x00000100f360c8> 
    from /Users/7stud/.rvm/gems/ruby-2.0.0-p481@sample_app2_gems/gems/activemodel-4.0.8/lib/active_model/attribute_methods.rb:439:in `method_missing' 
    from /Users/7stud/.rvm/gems/ruby-2.0.0-p481@sample_app2_gems/gems/activerecord-4.0.8/lib/active_record/attribute_methods.rb:168:in `method_missing' 
    from (irb):3 
    from /Users/7stud/.rvm/gems/ruby-2.0.0-p481@sample_app2_gems/gems/railties-4.0.8/lib/rails/commands/console.rb:90:in `start' 
    from /Users/7stud/.rvm/gems/ruby-2.0.0-p481@sample_app2_gems/gems/railties-4.0.8/lib/rails/commands/console.rb:9:in `start' 
    from /Users/7stud/.rvm/gems/ruby-2.0.0-p481@sample_app2_gems/gems/railties-4.0.8/lib/rails/commands.rb:62:in `<top (required)>' 
    from bin/rails:4:in `require' 
    from bin/rails:4:in `<main>' 

2.0.0-p481 :004 > user 
=> #<User id: 2, name: "Example User", email: "example@railstutorial.org", created_at: "2014-10-02 01:39:04", updated_at: "2014-10-02 01:39:04", password_digest: "$2a$10$VNzivk5opu1AC5DOM467dO2JaTg3c3JC9OAXR0AqvEi0..."> 

2.0.0-p481 :005 > x 
=> 10 

2.0.0-p481 :006 > 

請參閱？一切仍然存在。另一方面，如果通過"go back"表示"go back to the blissful state you were in when you got no errors"，則解決方案是在控制檯中輸入正確的命令。下一次，從您試圖模擬的教程中複製命令並將其粘貼到空白文本文件中，然後複製給出錯誤（但您知道是正確的錯誤！）的命令，並將其粘貼到命令教程：

User.first 
user.first 

然後比較它們。您的問題也可以通過從不創建與您的模型名稱相同的變量來減輕，例如而不是寫：

user = User.new(...) 

寫：

my_user = User.new(...) 

然後，如果你寫：

user.first 

您將得到錯誤：

NameError: undefined local variable or method `user' for main:Object 

這應該是更容易你去調試。