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我一直很难理解整个概念以及它在 Rails 中的工作原理，我认为它为您完成了工作，因为我习惯于手动构建关联。我目前有一个计费系统，我正在尝试创建一个订单部分，显然我的订单必须有很多产品，所以我已将数据库规范化为第 3 范式，以便订单和产品通过另一个链接名为ordered products 的表，该表包含订单ID 和产品ID，以及订购的产品数量。我已经根据我对 has_Many 的了解创建了模型：通过 Code School 教程在 Rails 中进行，但是我已经完全复制了他们的模型，但是我的模型和他们的模型之间肯定存在某种差异。

订购型号：

class Order < ActiveRecord::Base
  attr_accessible :ClientID, :OrderTotal
  has_many :orderedproducts
  has_many :products, through: :orderedproducts, :source => :product

end

订购产品型号：

class Orderedproduct < ActiveRecord::Base
  attr_accessible :OrderID, :ProductID, :QuantityOrdered
  belongs_to :order
  belongs_to :product
end

产品型号：

class Product < ActiveRecord::Base
    #This line makes these elements accessible outside of the class.
    attr_accessible :ProductName, :ProductPrice, :ProductQuantity, :ProductSupplier

    has_many :orderedproducts
    has_many :orders, through: :orderedproducts, :source => :order

    #These attributes ensure that the data entered for each element is valid and present.
    validates_presence_of :ProductName
    validates_presence_of :ProductPrice
    validates_numericality_of :ProductPrice
    validates_presence_of :ProductQuantity
    validates_numericality_of :ProductQuantity
    validates_presence_of :ProductSupplier

end

我添加了 source 属性，因为我在控制台中遇到错误，建议我应该将 source 属性添加到 has_many :through 行。这是我尝试将产品添加到订单时在控制台中收到的错误：

irb(main):017:0> order.products = Product.find(4)
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 4 LIMIT 1
ActiveRecord::HasManyThroughSourceAssociationNotFoundError: Could not find the source association(s) :ProductID in model Orderedproduct. Try 'has_many :products, :through => :orderedproducts, :source => <name>'. Is it one of :order or :product?
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/reflection.rb:509:in `check_validity!'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/associations/association.rb:26:in `initialize'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/associations/collection_association.rb:24:in `initialize'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/associations/has_many_through_association.rb:10:in `initialize'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/associations.rb:160:in `new'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/associations.rb:160:in `association'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/associations/builder/association.rb:51:in `block in define_writers'
        from (irb):17
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/railties-3.2.13/lib/rails/commands/console.rb:47:in `start'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/railties-3.2.13/lib/rails/commands/console.rb:8:in `start'
        from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/railties-3.2.13/lib/rails/commands.rb:41:in `<top (required)>'
        from script/rails:6:in `require'
        from script/rails:6:in `<main>'
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3 回答 3

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在这种情况下，它是 product= 方法；订单没有“产品”，它有很多“产品”。

你可以：

order.products << some_product

不幸的是，CamelCase 也是一个问题。Order 和 Product 的关联将分别查找 order_id 或 product_id，但不会找到它们。解决方案是将列名更改为 snake_case，或添加 :foreign_key => ... 选项。

于 2013-05-11T14:13:26.373 回答
0

我使用了错误的数组运算符，应该是 << 运算符而不是 = 运算符，因为我正在向数组中添加一个元素。

于 2013-05-11T13:44:06.103 回答
0

因为 Order has_many Products，你从 Rails 获得了一个#products 方法，而不是#product 方法。

您可以做的是使用您的 Order 实例创建相关的 OrderedProducts，并将 Product 添加到该实例。

order = Order.new
ordered_product = order.ordered_products.build
ordered_product.product = Product.find(4)

Order 上的#product 方法的问题在于它应该是一个集合，那么您的代码如何知道您的意思是哪一个？

于 2013-05-11T13:39:01.410 回答