为什么我不能为我的Rails应用程序构建一个ER图表？

Question

我在MacOSX10.10(约塞米蒂)上，我按照非常简单的指令运行graphviz here，这样我就可以为我的Rails应用程序获得一个实体关系图。

但这是行不通的：

$ brew install graphviz
==> Downloading https://downloads.sf.net/project/machomebrew/Bottles/graphviz-2.38.0.yosemite.bottle.1.tar.gz
Already downloaded: /Library/Caches/Homebrew/graphviz-2.38.0.yosemite.bottle.1.tar.gz
==> Pouring graphviz-2.38.0.yosemite.bottle.1.tar.gz
  /usr/local/Cellar/graphviz/2.38.0: 469 files, 68M

# Now I added gem 'rails-erd' to the Gemfile

$ bundle install 
<< SNIPPED SOME EXTRANEOUS OUTPUT HERE >>
Updating files in vendor/cache
  * choice-0.1.6.gem
  * ruby-graphviz-1.0.9.gem
  * rails-erd-1.1.0.gem
Your bundle is complete!
Use `bundle show [gemname]` to see where a bundled gem is installed.

$ bundle show rails-erd
/Users/myuser/.rvm/gems/ruby-1.9.3-p484@my-app-dir/gems/rails-erd-1.1.0

$ bundle exec rake erd --trace
rake aborted!
Don't know how to build task 'erd'
/Users/myuser/.rvm/gems/ruby-1.9.3-p484@my-app-dir/gems/rake-10.0.4/lib/rake/task_manager.rb:49:in `[]'
/Users/myuser/.rvm/gems/ruby-1.9.3-p484@my-app-dir/gems/rake-10.0.4/lib/rake/application.rb:142:in `invoke_task'
/Users/myuser/.rvm/gems/ruby-1.9.3-p484@my-app-dir/gems/rake-10.0.4/lib/rake/application.rb:101:in `block (2 levels) in top_level'

为什么rake文件不知道erd任务？我做了bundle exec rake -T，但它没有出现在那里。

Answer 1

这里有一个可行的解决办法。我可以使用irb代替：

$ bundler exec irb

1.9.3-p484 :001 > require './my_app.rb'
=> true

1.9.3-p484 :002 > require 'rails_erd/diagram/graphviz'
=> true

1.9.3-p484 :003 > RailsERD::Diagram::Graphviz.create
=> "erd.pdf"