我有一個關係總結2列的問題,有記錄,如:如何總結列有活動記錄關係軌
#<RequestProduct id: 26, request_id: 27, product_service_id: 9, quantity: 12, created_at: "2015-09-12 04:58:19", updated_at: "2015-09-12 04:58:19">,
#<RequestProduct id: 27, request_id: 27, product_service_id: 10, quantity: 11, created_at: "2015-09-12 04:58:19", updated_at: "2015-09-12 04:58:19">,
#<RequestProduct id: 28, request_id: 27, product_service_id: 11, quantity: 10, created_at: "2015-09-12 04:58:20", updated_at: "2015-09-12 04:58:20">
我要總結的模型RequestProduct數量與價格模型ProductService。我試圖用一些方式,但還是失敗了,我用這樣的方式:
@request.request_products.sum("quantity * request_products.product_service.price")
@request.request_products.sum("quantity * product_service.price")
@request.request_products.sum("quantity * ?", product_service.price)
有沒有其他辦法?
什麼是RDBMS? –