Question

If I have a query of the form

var query = from items in entityDb.TableName
            join requestedBy in entityDb.People on items.RequestedById equals requestedBy.PersonId in requestedByOuter
            from requestedBy in requestedByOuter.DefaultIfEmpty()
            select items;

Also assume this is a big query, 10 more joins. Then I have a conditional filter

if (!string.IsNullOrEmpty(phaseFilter))
{
   query = query.Where(item => item.Phase == phaseFilter);
}

At this point I believe I have lost the advantages of deferred execution. With 1000’s of results this can hurt performance. Considering my query is, in reality, 50 lines of code, I prefer not to go…

if(phaseFilter not null)
  //50 lines....
else if(filter2 not null)
  //50 lines...
else if (filter2 not null and phaseFilter not null)
  //50 lines...

ugh. Can I somehow have my cake and eat it too?

Answer 1

Nope, you don’t lose it. The execution is still deferred, because .Where just returns an IEnumerable<T> that filters the IEnumerable<T> passed to it, and it’s still deferred when you do that.