如何在左外加入 Linq 中使用包含

Question

我有这个查询

          from Room in PMSdb.Room_Tbl
                join Res in PMSdb.Reservation_Tbl on
                Room.Room_ID equals Res.Room_ID
                into ej
                from Res in ej.DefaultIfEmpty() 
                join Feature in PMSdb.Room_Features_Tbl on
                Room.Room_Features.Split(',').Contains(Feature.Room_Features_ID.ToString())
                into FE
                from Feature in FE.DefaultIfEmpty()
                  select new
                              {
                                  Room = Room.Room_Number,
                                  Room_type = RoomType.Room_Type_Code
                                  Feature =Feature.Feature_Name}

我需要这样做 Room.Room_Features.Split(',').Contains(Feature.Room_Features_ID.ToString()) 但它拒绝 我该怎么做？

Answer 1

您真的应该考虑使用联结表来规范化该数据，逗号分隔的字段是不良数据库设计的标志。

话虽如此，问题在于实体框架无法将string.Split() 转换为 SQL 查询。

如果您的数据存储为,val1,val2,,val3,（前缀和后缀都带有逗号，而逗号不是有效值），您可以使用string.Contains，可以翻译到 SQL：

Room.Room_Features.Contains($",{Feature.Room_Features_ID},")

Answer 2

这个怎么样：

(from Room in PMSdb.Room_Tbl
            join Res in PMSdb.Reservation_Tbl on
            Room.Room_ID equals Res.Room_ID
            into ej
            from Res in ej.DefaultIfEmpty()
            select new { room = Room, res = Res)
            .Where(x => x.Res == null)
            .Select(x => new {
                             Room = x.room.Room_Number,
                             Room_type = x.room.Room_Type_Code,
                             Features = x.room.Room_Features.Split(new char[] {','})
                                .Select(y => PMSdb.Room_Features_Tbl.Where(z => z.Room_Features_ID.ToString() == y.Trim()).FirstOrDefault())
                                .ToList() 
            }).ToList();