Question

我是C＃的新手，我有一个别人设计的数据库，查询效果很好，但与SQL相比，速度慢了10倍。

我肯定在这里犯了错误，任何人都有提示加快这一点。此模型用于在表格中显示，我将int转换为ENUM并计算显示的折扣。

代码是：

var results = from w in db.Washes.AsEnumerable()
              join t in db.Wash_Types.AsEnumerable() on w.WashTypeId equals t.Id
              join a in db.Accounts.AsEnumerable() on w.AccountId equals a.Id
              orderby w.Id descending
              select new AllWashesTable
                    {
                        Id = w.Id,
                        WashTime = w.WashTime,
                        WashTimeEnd = w.WashTimeEnd,
                        Name = a.Name,
                        Client = (w.Client != null ? w.Client.Naziv : ""),
                        MobileNumber = a.MobileNumber,
                        Identification = w.Identification,
                        WashType = WashTypeShowEnum.WashTypeShowEnumToString((WashTypeShowEnum.WashType) w.WashTypeId),
                        Price = int.Parse(t.WashPrice) * (1 - w.Discount) + "",
                        Discount = w.Discount
                    };
return results.ToList();

似乎我所有的实体查询都比SQL慢至少5倍。某处我犯了一些错误。

Answer 1

您的问题是使用AsEnumerable。当执行查询时（在您的情况下为results.ToList()），将使用linq-to-objects评估其后出现的所有内容。这意味着DB不会处理您的连接。您将从表中获取所有记录。

但是，实体框架无法识别您的函数WashTypeShowEnum.WashTypeShowEnumToString。

您可能希望将AsEnumerable移至结尾，然后select结果。

var results = (from w in db.Washes
              join t in db.Wash_Types on w.WashTypeId equals t.Id
              join a in db.Accounts on w.AccountId equals a.Id
              orderby w.Id descending
              select new {w, a, t}).AsEnumerable().Select(arg=> new AllWashesTable
                    {
                        Id = arg.w.Id,
                        WashTime = arg.w.WashTime,
                        WashTimeEnd = arg.w.WashTimeEnd,
                        Name = arg.a.Name,
                        Client = (arg.w.Client != null ? arg.w.Client.Naziv : ""),
                        MobileNumber = arg.a.MobileNumber,
                        Identification = arg.w.Identification,
                        WashType = WashTypeShowEnum.WashTypeShowEnumToString((WashTypeShowEnum.WashType) arg.w.WashTypeId),
                        Price = int.Parse(arg.t.WashPrice) * (1 - arg.w.Discount) + "",
                        Discount = arg.w.Discount
                    };
return results.ToList();

实体LINQ查询速度慢

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