新手又来提问了：关于rails4.0.0使用grape做api（ruby2.0.0）

[androidBrant]

新建的api文件 app/api/api.rb

http://gist.github.com/c6eb81aeebe4fa347b3b

在routes.rb中添加
mount JokesApi::API => "/"

修改application.rb

http://gist.github.com/6329221

添加gem gem ‘grape’

rails s 启动服务器报错，信息如下：

=> Booting WEBrick
=> Rails 4.0.0.rc1 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/Users/sjwu/Desktop/joke_app/config/routes.rb:5:in `block in <top (required)>': uninitialized constant JokesApi (NameError)
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/route_set.rb:315:in `instance_exec'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/route_set.rb:315:in `eval_block'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/actionpack-4.0.0.rc1/lib/action_dispatch/routing/route_set.rb:293:in `draw'
from /Users/sjwu/Desktop/joke_app/config/routes.rb:2:in `<top (required)>'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:40:in `block in load_paths'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:40:in `each'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:40:in `load_paths'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:16:in `reload!'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:26:in `block in updater'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/activesupport-4.0.0.rc1/lib/active_support/file_update_checker.rb:75:in `call'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/activesupport-4.0.0.rc1/lib/active_support/file_update_checker.rb:75:in `execute'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:27:in `updater'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/routes_reloader.rb:6:in `execute_if_updated'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application/finisher.rb:69:in `block in <module:Finisher>'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/initializable.rb:30:in `instance_exec'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/initializable.rb:30:in `run'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/initializable.rb:55:in `block in run_initializers'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:150:in `block in tsort_each'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:183:in `block (2 levels) in each_strongly_connected_component'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:219:in `each_strongly_connected_component_from'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:182:in `block in each_strongly_connected_component'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:180:in `each'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:180:in `each_strongly_connected_component'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/tsort.rb:148:in `tsort_each'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/initializable.rb:54:in `run_initializers'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/application.rb:214:in `initialize!'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /Users/sjwu/Desktop/joke_app/config/environment.rb:5:in `<top (required)>'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/backports-3.3.3/lib/backports/tools.rb:328:in `require'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/backports-3.3.3/lib/backports/tools.rb:328:in `require_with_backports'
from /Users/sjwu/Desktop/joke_app/config.ru:3:in `block in <main>'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/builder.rb:55:in `instance_eval'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/builder.rb:55:in `initialize'
from /Users/sjwu/Desktop/joke_app/config.ru:in `new'
from /Users/sjwu/Desktop/joke_app/config.ru:in `<main>'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/builder.rb:49:in `eval'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/builder.rb:49:in `new_from_string'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/builder.rb:40:in `parse_file'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/server.rb:277:in `build_app_and_options_from_config'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/server.rb:199:in `app'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/commands/server.rb:48:in `app'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/rack-1.5.2/lib/rack/server.rb:314:in `wrapped_app'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/commands/server.rb:75:in `start'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:80:in `block in <top (required)>'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:75:in `tap'
from /Users/sjwu/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:75:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'



高手帮忙看下，是啥原因，新学rails不久，搞不明白，为什么JokeApi文件没有自己加载？

谢谢。。。

[androidBrant]

第一个app： http://192.157.213.221 想作api来作移动端。搞几天了这错误搞不定。。

[coolzilj]

@androidBrant 修改`application.rb`文件了么？

[lichao]

怎么还是 RC1

[coolzilj]

@androidBrant 会不会是文件路径的原因，试下改成 app/api/jokes_api/api.rb

[reducm]

routes文件先require一下Api文件

[androidBrant]

@coolzilj 修改了
@coolzilj 路径会有影响吗？config.paths.add "app/api", glob: "**/*.rb"
config.autoload_paths += Dir["#{Rails.root}/app/api/*"] 这两句是不是对指定的api路径自动require？
@reducm config.paths.add "app/api", glob: "**/*.rb"
config.autoload_paths += Dir["#{Rails.root}/app/api/*"]这两句就是对指定的api路径自动require。。。

[androidBrant]

@lichao 哪个rc1？有碰到过类似的问题吗？还是有可能的解决办法？

[lichao]

@androidBrant 我意思是 Rails 4 早已正式 Release 了，你怎么还用 Release Candidate 1

[coolzilj]

@androidBrant 是自动require没错，但你没遵守rails里的文件命名惯例

[coolzilj]

@androidBrant

任何声明在 autoload paths 的 module 只有在 module 名字和父目录名相同时才会载入。
举个例子：

```ruby

# lib/my_stuff/bar.rb

module Foo
class Bar
end
end
```
注意文件名，这样子是不会正确自动载入的，但如果你改成 lib/foo/bar.rb 它就可以了。

关于autoload背后魔法的详细解释，可以参考这里

http://stackoverflow.com/questions/3356742/best-way-to-load-module-class-from-lib-folder-in-rails-3?answertab=active#tab-top

[androidBrant]

@coolzilj 哦，规则还是强制性的啊，我看看，Thank you

[hlxwell]

Rails 4 里 app 下的目录都会被加载，但是在 dev 环境下是默认 lazy loaded, 所以你需要手动 require 一下，或者在 routes.rb 顶上加上.

`Rails.application.eager_load! if Rails.env.development?`

就搞定了。