轨控制台--sandbox迈克尔·哈特尔的轨道教程第三版不知道这是如何工作

Question

我使用有一个问题与Ruby on Rails的：

rails console --sandbox 

所以在迈克尔·哈特尔的轨道教程第3版，我们正在使用此，我当我有时候使用它，并且一切顺利，然后出现错误，并且从字面上看，整个测试环境变得无用，因为它不会响应我的命令。例如，我将键入：

2.1.1 :025 > user.first 

，或者是工作，应该是工作，而是得到任何其他命令：

NoMethodError: undefined method `first' for #<User:0x007fede35e3188> 
    from /Users/andrewkim/.rvm/gems/[email protected]_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/[email protected]_rails_4.2.0.beta2 gems/railties-4.2.0.beta2/lib/rails/commands/console.rb:110:in `start' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2 gems/railties-4.2.0.beta2/lib/rails/commands/console.rb:9:in `start' 
    from /Users/andrewkim/.rvm/gems/[email protected]_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/[email protected]_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/[email protected]_rails_4.2.0.beta2/gems/railties-4.2.0.beta2/lib/rails/commands.rb:17:in `<top (required)>' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:248:in `require' 
    from /Users/andrewkim/.rvm/gems/[email protected]_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/[email protected]_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/[email protected]_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/[email protected]_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:242:in `load' 
    from /Users/andrewkim/.rvm/gems/[email protected]_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/[email protected]_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/[email protected]_rails_4.2.0.beta2/gems/activesupport-4.2.0.beta2/lib/active_support/dependencies.rb:242:in `load' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/commands/rails.rb:6:in `call' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/command_wrapper.rb:38:in `call' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:180:in `block in serve' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:153:in `fork' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:153:in `serve' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:128:in `block in run' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:122:in `loop' 
    from /Users/andrewkim/.rvm/gems/[email protected]_rails_4.2.0.beta2/gems/spring-1.1.3/lib/spring/application.rb:122:in `run' 
    from /Users/andrewkim/.rvm/gems/[email protected]_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 > 

突然什么，我在终端上键入将带着这样的错误，我不知道怎么去无需退出“rails console --sandbox”。有没有办法？

Answer 1

for example, I will type:

2.1.1 :025 > user.first 

or any other command that was working and should be working

该命令不应该工作，它不起作用。您遇到错误是因为在教程中有一个User实例，它表示表中的一行，例如

user = User.new(name: "Joe", email: "[email protected]") 

没有名为first()的方法。相反，用户实例具有以下方法：

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

然而，可以使用类名称（或型号名称）来搜索表格，例如，

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

至于这样的：

and I don't know how to go back

回去呢？什么也没有变。在错误发生之前，您输入到控制台的所有变量仍然存在。这里是一个轨道控制台的例子：

$ 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: "[email protected]") 
    User Load (4.0ms) SELECT "users".* FROM "users" WHERE "users"."email" = '[email protected]' LIMIT 1 
=> #<User id: 2, name: "Example User", email: "[email protected]", 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/[email protected]_app2_gems/gems/activemodel-4.0.8/lib/active_model/attribute_methods.rb:439:in `method_missing' 
    from /Users/7stud/.rvm/gems/[email protected]_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/[email protected]_app2_gems/gems/railties-4.0.8/lib/rails/commands/console.rb:90:in `start' 
    from /Users/7stud/.rvm/gems/[email protected]_app2_gems/gems/railties-4.0.8/lib/rails/commands/console.rb:9:in `start' 
    from /Users/7stud/.rvm/gems/[email protected]_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: "[email protected]", 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 > 

请参阅？一切仍然存在。另一方面，如果通过"go back"表示"go back to the blissful state you were in when you got no errors"，则解决方案是在控制台中输入正确的命令。下一次，从您试图模拟的教程中复制命令并将其粘贴到空白文本文件中，然后复制给出错误（但您知道是正确的错误！）的命令，并将其粘贴到命令教程：

User.first 
user.first 

然后比较它们。您的问题也可以通过从不创建与您的模型名称相同的变量来减轻，例如而不是写：

user = User.new(...) 

写：

my_user = User.new(...) 

然后，如果你写：

user.first 

您将得到错误：

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

这应该是更容易你去调试。