Rubyonrails Rails 可选的 belongs_to

我正在为库存管理编写Rails前端.我希望用户能够注册产品，因此我有:

class User < ActiveRecord::Base
  has_many :products
  # <snip>
end

和

class Product < ActiveRecord::Base
  belongs_to :user
  # <snip>
end

The problem is that products are created prior to being registered by a user. That is, it's perfectly acceptable to call Product.create 和 just have it set the user_id to nil. As you can imagine, though, Rails doesn't support this out of the box:

> Product.create!
   (0.3ms)  SELECT COUNT(*) FROM "products" WHERE "products"."type" IN ('Product')
   (0.1ms)  begin transaction
   (0.1ms)  rollback transaction
ActiveRecord::RecordInvalid: Validation failed: User can't be blank
    from ~/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/validations.rb:56:in `save!'

I've thought about a bunch of kludgey workarounds, the most appealing of which is to have a NullUser subclassing User 和 use that to create products. But that still seems like a hack. What's the Rails Way with this?

谢谢

相关迁移:

class AddUseridToProducts < ActiveRecord::Migration
  def change
    add_column :products, :user_id, :integer
  end
end

和 later:

class Changeuseridtobeoptionalforproducts < ActiveRecord::Migration
  def change
    change_column :products, :user_id, :integer, null: true
  end
end