Question

我正在学习Rails，其中包含Agile Web Development with Rails第4版。

考虑下面的迁移代码：

class CombineItemsInCart < ActiveRecord::Migration
  def up
    Cart.all.each do |cart|
      sums = cart.line_items.group(:product_id).sum(:quantity)

      sums.each do |product_id, quantity|
        if quantity > 1
          cart.line_items.where(product_id: product_id).delete_all
          cart.line_items.create(product_id: product_id, quantity: quantity)
        end
      end
    end
  end

  def down
    LineItem.where("quantity>1").each do |line_item|
      line_item.quantity.times do
        LineItem.create(cart_id: line_item.cart_id, product_id: line_item.product_id, quantity: 1)
      end
      line_item.destroy
    end
  end
end

发生以下错误：

==  CombineItemsInCart: migrating =============================================
rake aborted!
An error has occurred, this and all later migrations canceled:

Can't mass-assign protected attributes: quantity/home/richard/projects/pickaxe/mini-projects/depot-app/db/migrate/20130607003533_combine_items_in_cart.rb:9:in `block (2 levels) in up'
/home/richard/projects/pickaxe/mini-projects/depot-app/db/migrate/20130607003533_combine_items_in_cart.rb:6:in `each'
/home/richard/projects/pickaxe/mini-projects/depot-app/db/migrate/20130607003533_combine_items_in_cart.rb:6:in `block in up'
/home/richard/projects/pickaxe/mini-projects/depot-app/db/migrate/20130607003533_combine_items_in_cart.rb:3:in `each'
/home/richard/projects/pickaxe/mini-projects/depot-app/db/migrate/20130607003533_combine_items_in_cart.rb:3:in `up'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

现在我在某处读过这本书是在默认情况下需要attr_accessible之前编写的，但它还没有真正触及如何正确使用它。我尝试将：line_item或：line_items添加到Cart模型中的attr_accessible行，但没有运气。

有人可以教我这里发生的事情吗？

Answer 1

无法批量分配受保护的属性：数量

尝试attr_accessible：数量

您需要列出该列表中的所有属性。

Answer 2

您需要使属性可访问。在模型中：

class Object ActiveRecord::Base
  attrib_accessible :attrib1, :attrib2, :attrib3
end

显然你会用模型的属性替换attrib1等。

Answer 3

您尝试从迁移中访问大量属性。如果要从代码中访问数据库表属性，则需要允许对该属性进行批量分配，以告知模型您可以通过代码为字段分配数据。对于此pusrpose，只需将所需字段添加为attr_accessible，并针对您的问题特定解决方案：

类LineItem＆lt;的ActiveRecord ::基

attr_accessible：quantity，：product_id，：cart_id

端

Rails db：migrate无法批量分配受保护的属性

3 个答案: