Ruby on rails Rails实例变量nil仅在计数时可用

我有一个带有列的表

ticketlines

：

ID, TICKET, PRODUCT, REASON, UNITS, PRICE

管制员票务线：

  @q = Ticketline.joins(:product, :ticket).group(:PRODUCT).select("PRODUCT, products.CONSIGNOR, SUM(UNITS) AS TOTALUNITS").ransack(params[:q])
  @product_sales = @q.result.paginate(:page => params[:page], :per_page => 30)

在我看来，我想显示

@product\u sales.count

将生成一个查询：

SELECT COUNT(*) AS count_all, `ticketlines`.`PRODUCT` AS ticketlines_product FROM `ticketlines` INNER JOIN `products` ON `products`.`ID` = `ticketlines`.`PRODUCT` INNER JOIN `tickets` ON `tickets`.`ID` = `ticketlines`.`TICKET` GROUP BY `ticketlines`.`PRODUCT`

它显示@product_sales的结果数

问题是当我试图用ransack过滤结果时

Products表有列

ID、名称、类别、发货人

如果我按产品筛选票证行，它会起作用。如果我按类别或发货人筛选，则不会

例如，如果我在点击

@product\u sales.count

时按类别进行筛选，则生成查询：

SELECT COUNT(DISTINCT ) AS count, `ticketlines`.`PRODUCT` AS ticketlines_product FROM `ticketlines` INNER JOIN `products` ON `products`.`ID` = `ticketlines`.`PRODUCT` INNER JOIN `tickets` ON `tickets`.`ID` = `ticketlines`.`TICKET` LEFT OUTER JOIN `categories` ON `categories`.`ID` = `products`.`CATEGORY` WHERE `categories`.`ID` = '289108c2-6be3-4baf-b053-96f70dc2cc5a' GROUP BY `ticketlines`.`PRODUCT`

对我来说没有意义的是，如果我从view@product\u sales.count中删除，就没有错误。我可以使用类别过滤器，它的工作

执行的查询是：

SELECT  PRODUCT, SUM(UNITS) AS TOTALUNITS FROM `ticketlines` INNER JOIN `products` ON `products`.`ID` = `ticketlines`.`PRODUCT` INNER JOIN `tickets` ON `tickets`.`ID` = `ticketlines`.`TICKET` LEFT OUTER JOIN `categories` ON `categories`.`ID` = `products`.`CATEGORY` WHERE `categories`.`ID` = '289108c2-6be3-4baf-b053-96f70dc2cc5a' GROUP BY `ticketlines`.`PRODUCT` LIMIT 30 OFFSET 0

只有使用计数时，@product\U sales才为零的原因是什么