Ruby on rails RubyonRails：为什么.all成功了，而

以下是rails控制台的两个输出：

1.成功 2.失败

---

find:all语法在Rails 4中被删除。您可以使用Category.all来获得相同的结果。

您使用的是哪个Rails版本？该样式在4.0中被弃用，在4.1中被删除，因为您在4.2中不再使用了。如果你需要，你可以。使用，但是如果您正在编写新代码，您应该使用新的样式，因为gem不能与5一起使用

irb(main):038:0> Category.all
  Category Load (0.0ms)  SELECT "categories".* FROM "categories"
=> #<ActiveRecord::Relation [#<Category id: 1, name: "tutorials", created_at: "2016-05-14 18:44:38", updated_at: "2016-05-14 18:44:38">, #<Category id: 2, name: "news", created_at: "2016-05-14 18:44:38", updated_at: "2016-05-14 18:44:38">, #<Category id: 3, name: "design", created_at: "2016-05-14 18:44:38", updated_at: "2016-05-14 18:44:38">]>

irb(main):039:0> Category.find(:all)
  Category Load (0.0ms)  SELECT  "categories".* FROM "categories" WHERE "categories"."id" = $1 LIMIT 1  [["id", nil]]
ActiveRecord::RecordNotFound: Couldn't find Category with 'id'=all
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.2.3/lib/active_record/relation/finder_methods.rb:324:in `raise_record_not_found_exception!'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.2.3/lib/active_record/relation/finder_methods.rb:444:in `find_one'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.2.3/lib/active_record/relation/finder_methods.rb:423:in `find_with_ids'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.2.3/lib/active_record/relation/finder_methods.rb:71:in `find'
        from h:in `find'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.2.3/lib/active_record/core.rb:130:in `find'
        from (irb):39
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.2.3/lib/rails/commands/console.rb:110:in `start'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.2.3/lib/rails/commands/console.rb:9:in `start'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:68:in `console'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
        from h:/rails/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/railties-4.2.3/lib/rails/commands.rb:17:in `<top (required)>'
        from bin/rails:4:in `require'
        from bin/rails:4:in `<main>'
irb(main):040:0>