实体LINQ查询变慢

Question

I'm new to the C#, I have a database that someone else designed, query works great, but compared with SQL, it's 10 times slower.

I made mistakes here for sure, anybody have tips to speed this up a little bit. This model is for displaying in table, and I converting int to ENUM and calculating discount for display.

Code is:

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();

Seems all my entity queries are at least 5+ times slower than SQL. Somewhere I am making some mistake.

Answer 1

Your problem is the use of AsEnumerable . When the query gets executed (in your case the results.ToList() ), Everything that appears after it, will be evaluated using linq-to-objects. It means that your joins will not be handled by DB. You will fetch all the records from the tables.

However, your function WashTypeShowEnum.WashTypeShowEnumToString will not be recognized by entity framework.

You might want to move the AsEnumerable to the end and then select the results.

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();