How to improve Linq-To-Sql code

Question

Using the StackExchange.Profiling.MiniProfiler class to profile an ASP.NET MVC application with Linq-To-Sql as ORM.

I'm trying to reduce one action to one SQL, so that I don't have any duplicates anymore. So I changed my linq-to-sql code accordingly, but it didn't have any positive effect on the speed.

Then I checked the time that is needed for the SQL.

This shows the MiniProfiler:

When I fire up the exact same SQL in Management Studio it is super fast:

Here is the code:

from t in type
let tDoc = (from d in context.documents
            where d.Key == t.No
            && d.RType == (int)RType.Art
            && d.AType == (int)AType.Doc
            select d).FirstOrDefault(d => d.UseForThumb)
select new Time
{
    Id = t.Id,
    //... more simple mappings here
    // then a complex one:
    DocsCount = context.documents.Count(d =>
        (d.Key == t.Id.ToString()
        && d.RType == (int)RType.Type
        && d.AType == (int)AType.Doc)
        ||
        (d.Key == t.No
        && d.RType == (int)RType.Art
        && d.AType == (int)AType.Doc)),

    // and another one
    ThumbId = (tDoc != null && tDoc.FRKey.HasValue) ? tDoc.FRKey.Value : 0
};

What can be the reason for the huge difference? - Edit: There is no difference, I just misenterpreted SSMS :(

Anyway, my problem persits. What could I change to make it faster?

I read sometime that the mapping from Linq-To-Sql has a performance problem. Is there a way to workaround this?

Answer 1

I did some trial and error and changed the Linq-To-Sql code to this:

from t in types
let docs = context.documents.Where(d => (d.RKey == t.Id.ToString()
                                     && d.RType == (int)RType.Type
                                     && d.AType == (int)AType.Doc)
                                   ||
                                        (d.RKey == t.No 
                                     && d.RType == (int)RType.Art 
                                     && d.AType == (int)AType.Doc))
let tDoc = docs.FirstOrDefault(d => d.RType == (int)RType.Art && d.UseForThumb)
let docsCount = docs.Count()
select new Time
{                                               
  Id = t.Id,
  //... more simple mappings here
  DocsCount = docsCount,
  ThumbId = (tDoc != null && tDoc.FRKey.HasValue) ? tDoc.FRKey.Value : 0,
}

This made the query much, much faster.