sql - 没有 UNION 的库存 SQL 查询？

Question

我正在设计一个库存系统，它有用户、产品、buy_leads、订单(授权购买线索)、输入和输出。

class Product < ActiveRecord::Base
  has_many :buy_leads
end

class BuyLead < ActiveRecord::Base
  belongs_to :product
  has_one :order
end

class Order < ActiveRecord::Base
  belongs_to :buy_lead
  belongs_to :user, :foreign_key => :authorized_by
  has_many :inputs
end

class Input < ActiveRecord::Base
  belongs_to :order
  has_many :outputs
end

class Output < ActiveRecord::Base
  # Associations
  belongs_to :input
  belongs_to :user
end

输入和输出有一个数量值。为了获得产品库存和特定产品库存，我在两个原始 SQL 查询中使用 UNION，通过使输出数量为负数，然后分组和将它们加在一起:

class InventoryController < ApplicationController

  def index
    @inventory = Input.find_by_sql products_inventory_sql
  end

  def show
    @inventory = Input.find_by_sql product_inventory_sql(params[:id])
  end

private

  def inputs_sql
    "SELECT b.*, p.*, i.order_id,
            i.id AS input_id,
            i.quantity AS quantity     
     FROM inputs i
          JOIN orders r ON r.id = i.order_id
          JOIN buy_leads b ON b.id = r.buy_lead_id
          JOIN products p ON p.id = b.product_id"
  end

  def outputs_sql
    "SELECT b.*, p.*, i.order_id,
            i.id AS input_id,
            (o.quantity * -1) AS quantity
     FROM outputs o
          JOIN inputs i ON i.id = o.input_id
          JOIN orders r ON r.id = i.order_id
          JOIN buy_leads b ON b.id = r.buy_lead_id
          JOIN products p ON p.id = b.product_id"
  end

  def products_inventory_sql
    "SELECT *, SUM(quantity) AS remaining_qty
     FROM (#{inputs_sql} UNION #{outputs_sql})
     GROUP BY product_id"
  end

  def product_inventory_sql(id)
    "SELECT *, SUM(quantity) AS remaining_qty
     FROM (#{inputs_sql} UNION #{outputs_sql})
     WHERE product_id = #{id}
     GROUP BY order_id, input_id"
  end

end

它有效，但我想使用 named_scope 的特性在 ActiveRecord 中链接查询并能够执行以下操作:

Product.inputs.by_product(id)
Product.inventory.by_product(id)
...

任何想法，或者我是否必须更改模式以获得更方便的模式？谢谢!

Answer 1

解决这个问题的可能性太多了，你到底想从这些报告中得到什么？

买单？产品？输入/输出？

(我将此作为答案发布，因为我无法对您的问题发表评论，如果您能启发我，我会更新答案)

更新

试试这个

#on input
named_scope :by_product, lambda {|id| {:joins => {:orders => {:buy_leads => :products}}, :conditions => ['products.id = ?', id]}}

您可以通过调用获取与该产品 ID 匹配的输入

Input.by_product(25)

如果那是您正在寻找的，我认为您现在也可以设法按产品进行输出:]