Rails的约定优于配置和Ruby的动态性，使得model类变得十分简洁，但是也带来了一个问题：如果你想知道一个model有哪些属性时，必须去查看数据库或者migration，这给开发带来了极大的不便。Annotate models插件很好地解决了这个问题，它在model类的起始处以注释的形式写明了所有的属性，下面来看个例子：
1. 创建工程：
$rails test_annotate_models
$cd rails test_annotate_models
2. 安装插件：
$script/plugin install http://repo.pragprog.com/svn/Public/plugins/annotate_models
3. 生成测试模型：
$script/generate model post title:string body:text
$rake db:migrate
4. 生成annotation：
$rake annotate_models
5. 效果：
# == Schema Information
# Schema version: 1
#
# Table name: posts
#
# id :integer not null, primary key
# title :string(255)
# body :text
# created_at :datetime
# updated_at :datetime
#
class Post ActiveRecord::Base
end
6. 增加模型：
$script/generate model comment body:text post:references
$script/generate migration add_comment_count_to_post
#db/migrate/003_add_comment_count_to_post.rb
class AddCommentCountToPost ActiveRecord::Migration
def self.up
add_column :posts, :comment_count, :integer
end
def self.down
remove_column :posts, :comment_count
end
end
$rake db:migrate
7. 再试试annotation：
$rake annotate_models
8. 效果：
# == Schema Information
# Schema version: 3
#
# Table name: posts
#
# id :integer not null, primary key
# title :string(255)
# body :text
# created_at :datetime
# updated_at :datetime
# comment_count :integer
#
class Post ActiveRecord::Base
end
# == Schema Information
# Schema version: 3
#
# Table name: comments
#
# id :integer not null, primary key
# body :text
# post_id :integer
# created_at :datetime
# updated_at :datetime
#
class Comment ActiveRecord::Base
end
