Question

我一直有点难以理解整个有很多概念以及它如何在Rails中运行，我认为它可以为你工作，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，所以我将数据库规范化为第三范式，以便订单和产品通过另一个链接表名为有序产品，此表包含订单的ID和产品的ID，以及订购的产品数量。我根据我所知道的has_Many创建了模型：通过代码学校教程中的Rails，然而我已经完全复制了它们的方式，但是我和它们之间必定存在某些区别。这是我目前拥有的模型文件：

订单型号：

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，因为我在控制台中收到错误，建议我将source属性添加到has_many：through行。当我尝试将产品添加到订单时，这是我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>'

Answer 1

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中的关联将分别查找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 =＆gt; ......选项。

Answer 2

因为订单has_many产品，你从Rails获得#products方法，而不是#product方法。

您可以使用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)

订单上#product方法的问题是有一个集合，那么你的代码如何知道你的意思？

Answer 3

我使用了错误的数组运算符，应该是＆lt;＆lt;运算符而不是=运算符，因为我在数组中添加了一个元素。

Rails：麻烦有许多关系

3 个答案: