我有一个关系总结2列的问题,有记录,如:如何总结列有活动记录关系轨
#<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">
我要总结的模型RequestProduct数量与价格模型ProductService。我试图用一些方式,但还是失败了,我用这样的方式:
@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)
有没有其他办法?
什么是RDBMS? –