How to write dynamic Linq2Sql compiled queries?

Question

I'm having performance issues with Linq2Sql compared to raw ADO.NET which has led me down the path of compiled queries. I have got this far so far

public static readonly Func<MyDataContext, WebServices.Search.Parameters, IQueryable<image>>
    Compiled_SelectImagesLinq = 
        CompiledQuery.Compile<MyDataContext, WebServices.Search.Parameters, IQueryable<image>>(
            (dc, parameters) =>  from i in dc.images
                  join l in dc.links on i.image_id equals l.image_id
                  join r in dc.resolutions on i.image_id equals r.image_id
                  where i.image_enabled == true && i.image_rating >= parameters.MinRating
                  && i.image_rating <= parameters.MaxRating
                  select i
      );

However I can't figure out how to add the extra optional parameters to the query as I currently do

if (parameters.Country != null)
{
    query = query.Where(x => x.image_country_id == parameters.Country);
}

if (parameters.ComponentId != null)
{
    query = query.Where(x => x.links.Any(l => l.link_component_id == parameters.ComponentId));
}

etc, etc

I tried writing another function which does

var query = Compiled_SelectImagesLinq(parameters);

and then adding the extra parameters to the query and returning

return query.Distinct().Take(parameters.Results);

Bit this doesn't seem right and returns no results

Answer 1

Have a look at this article. It may not do what you need (especially since you are compiling your queries), but anytime someone mentions Dynamic and Linq in the same sentence, I refer them to this article:

Dynamic LINQ: Using the LINQ Dynamic Query Library

http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

Answer 2

You'd have to benchmark your specific query, but often queries must be used 10-20 times before compiled query performance improvements equal the overhead. Also, how are you adding parameters to the where clause?

Additionally, dynamic compiled queries seems a bit of a mismatch. The Dynamic LINQ query library will do what you need but I don't think you'll get the compiled query performance improvement you want.