Linq on Linq without database roundtrip: speed issue

I have a speed problem in the following situation:

The SQL Server DB is hosted in a shared hosting environment, accessed through DSL 2MBytes line

There is a table of competition results which holds some 32 rows per competition.

When I display the result rows for a given competition in a datagridview, I use LINQ to produce the dgv datasou开发者_JAVA技巧rce, and THEN I add an extra computed column.

Why then adding a column? **Because the value of Row1.extraColumn depends on the value of Row1.Result compared to Row2.result**

I wrote:

dim mainQuery = from c in competResults 
                where competID = xxx 
                select c.resultID,  c.resultPosition, c.result

dataGridView1.datasource = mainQuery.ToList

'Prepare and add Exrta Column

dataGridView1.ADD Extra Column

Remember the dgv have only some 32 rows... Only...

Using LINQ I have a subquery like this:

dim rowA = from q in mainQuery where rowNumber = xxx select q
dim rowB = from q in mainQuery where rowNumber = yyy select q

Perform the calculation and write the result within dgv, like:

for each R in dgv.rows
  if R.cells("rowNumber").value = rowA.RowNumber then R.cells("ExtraColumn)).value = some result
  if R.cells("rowNumber").value = rowB.Rownumber then R.cells("ExtraColumn)).value = some result
next

And THAT takes some 30 seconds to 1 minute

I thought LINQ wouldn't go back to query the DB when querying a query whose results has been searched (When I performed the dataGridView1.datasource = CResults.ToList).

Of course, I can do the job iterating through the DGV rows, but I was more like using LINQ...

Any hint welcome...

To make sure your query is executed once only and mainQuery is local, change your first query to:

dim mainQuery = (from c in competResults 
                 where competID = xxx 
                 select c.resultID,  c.resultPosition, c.result).ToList()