I have a table in my database with, lets say 50 000 rows. I´m using a layered design with dal, bll and presentation.

I want to display 20 rows from the database, sorted by i.e. expireDate. I have tested there approaches:

DAL with IQueryble that returns an IQueryble of cmsDocuments:

var res = (from docs in db.cmsDocuments
select docs);

return res;

Then binding this to a grid in the presentation.

gw.DataSource = cmsDocuments.GetAll().OrderBy(x => x.documentUser == 1).OrderBy(x=>x.expireDate).Take(15);

This job gets done in around 0.04 seconds.

But using another approach would be to call the ToList() method on the res-collection in the DAL:

var res = (from docs in db.cmsDocuments
select docs);

return res.ToList();

This will execute the query and get me all the 50 000 rows, then in my presentation (or most likey BLL) I would to the sorting:

gw.DataSource = cmsDocuments.GetAll().OrderBy(x => x.documentUser == 1).OrderBy(x => x.expireDate).Take(15);

This job gets done in around 0.35 seconds. Big difference.

My question – is the best solution to put lots of methods in the DAL, like
GetTopTeen, GetAllActive etc, and then sort dem later on?

OR is it okey to send IQuerybles to the BLL and from there make all these methods?

Both L2S and EF use an identity map to track the objects each DataContext / ObjectContext instantiates.

See: http://odetocode.com/Blogs/scott/archive/2008/12/07/12372.aspx