DataMapper Association迁移

Question

我正在使用Padrino和DataMapper，我正在尝试进行迁移，以便为模型添加关联。例如，我从这开始：

class User
  include DataMapper::Resource

  property :id, Serial
  property :name, String
end

class Post
  include DataMapper::Resource

  property :id, Serial
  property :title, String
  property :body, Text
end

class Comment
  include DataMapper::Resource

  property :id, Serial
  property :name, String
end

我以下结尾：

class User
  include DataMapper::Resource

  property :id, Serial
  property :name, String

  has n, :posts
end

class Post
  include DataMapper::Resource

  property :id, Serial
  property :title, String
  property :body, Text

  belongs_to :user
  has n, :comment
end

class Comment
  include DataMapper::Resource

  property :id, Serial
  property :name, String

  belongs_to :post
end

我已经有了创建三个表的迁移，但我没有添加关联。为代码创建迁移的代码是什么？

Answer 1

DataMapper.auto_upgrade！将添加新的FK属性

Answer 2

auto_upgrade很不错，但不允许逐步退回。

migration 3, :create_products do
  up do
    modify_table :post do
      add_column :user_id, Integer
    end
    modify_table :comment do
      add_column :post_id, Integer
    end
  end

  down do
    modify_table :post do
      drop_column :user_id, Integer
    end
    modify_table :comment do
      drop_column :post_id, Integer
    end
  end
end

就是这样。