我在终端输入：

rails g migration rename_blog

然后在生成的 migration 文件里面写：

class RenameBlog < ActiveRecord::Migration
  def up
    rename_table :blogs, :articles
  end

  def down
    rename_table :articles, :blogs
  end
end

rake db:migrate之后，在 schema 里面看到：

ActiveRecord::Schema.define(:version => 20120829053310) do

  create_table "articles", :force => true do |t|
    t.datetime "created_at", :null => false
    t.datetime "updated_at", :null => false
    t.text     "content"
    t.string   "author"
  end

end

已经更改过来了，但是我尝试：

rails c
1.9.3p194 :004 > Article.column_names
#以下是返回的错误
NameError: uninitialized constant Article
    from (irb):4
    from /Users/Yuwen/.rvm/gems/ruby-1.9.3-p194/gems/railties-3.2.8/lib/rails/commands/console.rb:47:in `start'
    from /Users/Yuwen/.rvm/gems/ruby-1.9.3-p194/gems/railties-3.2.8/lib/rails/commands/console.rb:8:in `start'
    from /Users/Yuwen/.rvm/gems/ruby-1.9.3-p194/gems/railties-3.2.8/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

我搜索了一下，改原先的 model 类名Blog改为Article,并且把该文件blog.rb改为article.rb之后，还是这样。

另外那个up和down方法的意思不是很明确，怎么又是颠倒过来，哪个是上，哪个是下？