如何生成迁移以使引用具有多态性

Question

我有一个Products表,想要添加一列:

t.references :imageable, :polymorphic => true

我试图通过以下方式为此生成迁移:

$ rails generate migration AddImageableToProducts imageable:references:polymorphic

但我显然做错了.任何人都可以提出任何建议吗？谢谢

当我在生成迁移后尝试手动将其放入时,我这样做:

class AddImageableToProducts < ActiveRecord::Migration
  def self.up
    add_column :products, :imageable, :references, :polymorphic => true
  end

  def self.down
    remove_column :products, :imageable
  end
end

它仍然没有奏效

Answer 1

你想要做的还没有在稳定版本的rails中实现,所以Brandon的答案现在是正确的.但是这个功能将在rails 4中实现,并且已经在边缘版本中可用,如下所示(根据此CHANGELOG):

$ rails generate migration AddImageableToProducts imageable:references{polymorphic}

Answer 2

据我所知,没有用于多态关联的内置生成器.生成空白迁移,然后根据需要手动修改.

更新:您需要指定要更改的表.根据这个SO回答:

class AddImageableToProducts < ActiveRecord::Migration
  def up
    change_table :products do |t|
      t.references :imageable, polymorphic: true
    end
  end

  def down
    change_table :products do |t|
      t.remove_references :imageable, polymorphic: true
    end
  end
end

Answer 3

您还可以执行以下操作:

class AddImageableToProducts < ActiveRecord::Migration
  def change
    add_reference :products, :imageable, polymorphic: true, index: true
  end
end

Answer 4

你可以试试 rails generate migration AddImageableToProducts imageable:references{polymorphic}