加入不工作正常

Question

我得到了下面的SQL，我試圖將其轉換成活動記錄查詢方法

我有以下表

Customers (id, name) 
CustomerPriceRelations (customer_id, sales_price_id) # jointable 
SalesPrices (id, margin) 
ProductSalesPrices (product_id, sales_price_id) # jointable 

，我試圖執行下面的查詢

SELECT sp.id, sp.margin_percentage 
        FROM sales_prices sp 
        LEFT OUTER JOIN carrier_product_Sales_Prices ps 
         ON sp.id = ps.sales_price_id 
        LEFT OUTER JOIN Customer_Price_Relations cr 
         ON ps.sales_price_id = cr.sales_price_id 
        LEFT OUTER JOIN Customers c 
         ON cr.customer_id = c.id 
        WHERE c.id = 2 AND ps.carrier_product_id = 3 

我試過使用連接方法，但結果從來沒有加入由於某種原因，任何幫助嗎？

SalesPrice.joins(:carrier_products, :customers).where(customer_id: 2, carrier_product_id: 3) 

Answer 1

連接（）的Rails標準行爲是INNER JOIN，而不是LEFT OUTER JOIN。 INNER JOIN意思是，除非有匹配，否則連接的兩邊都不會出現。如果要使用LEFT OUTER JOIN，則需要明確定義它：

SalesPrice.joins("LEFT OUTER JOIN carrier_product_Sales_Prices ps ON sales_prices.id = ps.sales_price_id"). 
      joins("LEFT OUTER JOIN Customer_Price_Relations cr ON ps.sales_price_id = cr.sales_price_id"). 
      joins("LEFT OUTER JOIN Customers c ON cr.customer_id = c.id"). 
      where("cr.customer_id = ? and carrier_product_id = ?", 2, 3)