DataMapper关联迁移

Question

我正在使用DataMapper的Padrino，并且我正在尝试进行迁移，以便将关联添加到模型中。例如，我从以下内容开始：

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

我以以下几点作为结束：

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

我已经有了创建这三个表的迁移，但没有添加关联。为关联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很好，但不允许增量后退。

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

就这样。