Question

我正在设计库存系统，它有用户，产品， buy_leads ，订单（授权的buy_leads），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

输入和输出具有数量值。要获取产品库存和特定产品库存，我在两个原始SQL查询中使用UNION，输出数量为负，然后分组和把它们总结在一起：

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的功能来链接ActiveRecord中的查询，并能够执行以下操作：

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

任何想法，还是我必须更改架构以获得更方便的架构？谢谢！

Answer 1

如果没有数据我无法测试，但我认为应该是这样的：

SELECT
        b.*, p.*, i.order_id, i.id AS input_id, i.quantity AS quantity, -o.quantity AS quantity,
        (i.quantity - COALESCE(o.quantity,0)) AS remaining_qty
FROM
        products p
        JOIN buy_leads b ON b.product_id = p.id
        JOIN orders r ON r.buy_lead_id = b.id
        JOIN inputs i ON i.order_id = r.id
        LEFT JOIN outputs o ON o.input_id = i.id

Answer 2

当有多个“输出”记录时，Victor的解决方案失败，因为连接将通过输入和输出复制产品。

相反，您应该使用派生表而不是实际表来JOIN。没有数据，这很难测试和演示，但你应该尝试这样的事情：

    "SELECT b.*, p.*, i.order_id,
        i.id AS input_id,
        i.quantity AS quantity,
ISNULL(z.negquantities,0) negquantities,
i.quantity + ISNULL(z.negquantities,0) sumquantities

 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
  JOIN 
    (SELECT SUM(-1 * o.quantity) NegQuantities, o.input_id FROM outputs o GROUP BY o.input_id) z
    ON z.input_id = i.id

您会看到您正在加入输出表的总和，按输入ID分组，而不是输出表本身。这消除了联接中的意外行重复。当然，您可以在派生表的“ON”列表或“Where”子句中添加更多元素（我称之为“z”）这应该可以帮助你完成大部分工作。或者，发布数据库图表，以便我们更好地理解您的表格关系。

没有UNION的库存SQL查询？

3 个答案: