僅查詢最高投票數

Question

//query the list of winners of the said event
    public ActionResult List_of_Winners(int id=0) {
        var winners = (from cat in db.Events_Category_tbl
            join can in db.Candidates_Info_tbl on cat.events_category_id equals can.events_category_id
            where cat.events_info_id == id
            select new Candidates
            {
                events_category_name = cat.events_category_name,
                candidates_fullname = can.candidates_fullname,
                candidates_info_id = can.candidates_info_id,
                events_category_id = cat.events_category_id,
                no_of_votes = can.no_of_votes.Value
            }).Take(1).OrderBy(x=>can.no_of_votes);

        return PartialView(winners);
    }

在此代碼中，Iam計划在每個類別中獲得最高的no_of_votes。 但是，我對此有一個錯誤。 如何查詢數據庫以獲取所需的數據？

這是顯示的錯誤：“名稱”可以“在當前上下文中不存在”

Answer 1

您需要將訂單移至有待取貨/取貨的地方，我相信這樣的方法應該可以工作：

var winners = from cat in db.Events_Category_tbl
              from can in
                  (from c in db.Candidates_Info_tbl
                   where c.events_category_id == cat.events_category_id
                   select c).OrderByDescending(c => c.no_of_votes).Take(1)
              where cat.events_info_id == id
              select new Candidates
              {
                  events_category_name = cat.events_category_name,
                  candidates_fullname = can.candidates_fullname,
                  candidates_info_id = can.candidates_info_id,
                  events_category_id = cat.events_category_id,
                  no_of_votes = can.no_of_votes.Value
              };

---

對於類似的關系，可能會起作用（應該返回每個類別中得分最高的每個人）：

var winners = from cat in db.Events_Category_tbl
              from max_votes in
                  (from c in db.Candidates_Info_tbl
                   where c.events_category_id == cat.events_category_id
                   select c.no_of_votes).OrderByDescending(c => c).Take(1)
              join can in db.Candidates_Info_tbl on cat.events_category_id equals can.events_category_id
              where cat.events_info_id == id && can.no_of_votes == max_votes
              select new Candidates
              {
                  events_category_name = cat.events_category_name,
                  candidates_fullname = can.candidates_fullname,
                  candidates_info_id = can.candidates_info_id,
                  events_category_id = cat.events_category_id,
                  no_of_votes = can.no_of_votes.Value
              };

我想也可以使用GroupBy或不同樣式的內部查詢來完成，但是“從x in（從z中的y，其中y.something = x.something選擇某物）。Take（n）”模式導致交叉/外部適用於SQL Server，在我所見過的大多數情況下，它似乎表現良好。