ActiveRecord has_one引用同一個類的實例

Question

我有一個類，Page。我想打電話給page.next_page甚至page.page以獲得下一頁。 當我創建一個新的Page時，我想要關聯分配我的Book中的最後一個頁面以創建我創建的新Page的next_page。

class AddNextPageToPages < ActiveRecord::Migration 
    def change 
    add_column :pages, :page, :references 
end 
end 

此遷移失敗。

```

-- add_column(:pages, :next_page, {:class_name=>"Page"}) 
rake aborted! 
An error has occurred, this and all later migrations canceled: 

undefined method `to_sym' for {:class_name=>"Page"}:Hash/Users/username/.rvm/gems/ruby-1.9.3-p327/gems/activerecord-3.2.12/lib/active_record/connection_adapters/sqlite_adapter.rb:395:in  `valid_alter_table_options' 

```

Answer 1

您可以閱讀軌http://guides.rubyonrails.org/v3.2.13/migrations.html辦理遷移。