rails4 has_one 关联范围与 where 查询

Question

我正在开发一个产品模型，它与自身具有 has_one 关联，包括原材料记录。模型通过 REST API 返回数据。我正在使用 Active Model Serializer 而不是 JBuilder。

产品型号有一个“代码”字段，其中包含字符串中的产品代码：

'001-000-01-01' (This is a product.)
'001-000-00-01' (This is a material.)

两个代码之间的唯一区别是右起第三个数字。 “1”是产品。 “0”是物质。我想在检索产品记录时包含“raw_material”记录。因此，我尝试设置 has_one 与具有“where”子句的范围的关联（稍后我可以编写查询以从产品代码中获取材料）。现在我只需在 lambda 中传递“产品”对象并在 where 中使用它。

首先我在 def raw_material 中写，这行得通。但是，我不知道如何将对象传递给 def 并在 where 子句中使用它。因此，我在 has_one 中提出了范围模式，但是即使它生成与 def 模式完全相同的 SELECT，它也会返回错误。我得到的是“NoMethodError”。

class Product < ActiveRecord::Base
  has_many :supplies, ->{order('row_order ASC') }, primary_key: :code, foreign_key: :product_code
  #This Works!
  #has_one :raw_material, class_name: 'Product', primary_key: :code, foreign_key: :code
  #This Works!
  #has_one :raw_material
  #Does not work. Why?
  has_one :raw_material, ->(product) { where('code = ?', product.code).take }, class_name: 'Product'
  accepts_nested_attributes_for :supplies, allow_destroy: true

  #def raw_material
  #  Product.where('code = ?', '001-000-01-01').take
  #end
end

“def”模式有效：

Started GET "/products/1.json" for ::1 at 2016-10-05 21:48:15 +0900
Processing by ProductsController#show as JSON
  Parameters: {"id"=>"1"}
  Product Load (0.3ms)  SELECT  "products".* FROM "products" WHERE "products"."id" = ? LIMIT 1  [["id", 1]]
[active_model_serializers]   Supply Load (0.1ms)  SELECT "supplies".* FROM "supplies" WHERE "supplies"."product_code" = ?  ORDER BY row_order ASC  [["product_code", "031-052-00-01"]]
[active_model_serializers]   Product Load (0.1ms)  SELECT  "products".* FROM "products" WHERE (code = '001-000-01-01') LIMIT 1
[active_model_serializers] Rendered ProductSerializer with ActiveModelSerializers::Adapter::Attributes (6.71ms)
Completed 200 OK in 24ms (Views: 9.2ms | ActiveRecord: 1.4ms)

但是，范围模式不起作用：

Started GET "/products/1.json" for ::1 at 2016-10-06 08:19:13 +0900
Processing by ProductsController#show as JSON
  Parameters: {"id"=>"1"}
  Product Load (0.1ms)  SELECT  "products".* FROM "products" WHERE "products"."id" = ? LIMIT 1  [["id", 1]]
[active_model_serializers]   Supply Load (0.1ms)  SELECT "supplies".* FROM "supplies" WHERE "supplies"."product_code" = ?  ORDER BY row_order ASC  [["product_code", "031-052-00-01"]]
[active_model_serializers]   Product Load (0.1ms)  SELECT  "products".* FROM "products" WHERE (code = '031-052-00-01') LIMIT 1
[active_model_serializers] Rendered ProductSerializer with ActiveModelSerializers::Adapter::Attributes (10.6ms)
Completed 500 Internal Server Error in 27ms (ActiveRecord: 1.2ms)

NoMethodError (undefined method `except' for #<Product:0x007fe97b090418>):
  app/controllers/products_controller.rb:17:in `block (2 levels) in show'
  app/controllers/products_controller.rb:14:in `show'


  Rendered vendor/bundle/ruby/2.2.0/gems/actionpack-4.2.5/lib/action_dispatch/middleware/templates/rescues/_source.erb (8.8ms)

产品控制器简单地定义显示如下：

# GET /products/1
# GET /products/1.json
def show
  respond_to do |format|
    format.html
    format.json do
      render json: @product, include: ['raw_material']
    end
  end
end 

product_serializer.rb 是：

class ProductSerializer < ActiveModel::Serializer
  attributes(*Product.attribute_names.map(&:to_sym))
  has_one :raw_material
end

非常感谢任何帮助。

谢谢

更新：

我自己解决了这个问题。请在下面查看我的答案。感谢所有编写解决方案的人。

Answer 1

 # Does not work. Why?
 has_one :raw_material ->(product) { where('code = ?', product.code).take }...

因为您试图在此处定义范围...而不是关联。如果你想要一个范围，请使用一个范围，例如：

scope :raw_material ->(product) { where('code = ?', product.code).first }

如果您想要关联，请使用关联，例如

has_one :raw_material, class_name: 'Product', primary_key: :code, foreign_key: :code

不要试图将两者混为一谈。

Answer 2

您可以按如下方式自定义 has_one :raw_material。

class ProductSerializer < ActiveModel::Serializer
  attributes(*Product.attribute_names.map(&:to_sym))

  has_one :raw_material do
    Product.where(code: object.code)
  end

end

Answer 3

我可以自己解决这个问题。因为我不必写成一行，所以 def(method) 模式是最好的选择。如何覆盖“has_many”可以帮助我解决问题。

Overriding a has_many association getter

"self" 可用于 has_one 获取 def 中的对象。

has_one :raw_material

def raw_material
  Product.where('code like ?', (self.code)[0,9] + '_' + (self.code)[10,3]).take
end

这很有效，可以在模型中生成您喜欢的任何数据集。