Question

I want to retrieve commissions with a certain order number.

This works:

var expression = from commission in db.Auftraege 
                         where commission.Auftragsnummer == orderNbr
                         select new Commission() { EF_Commission = (commission as Auftrag) };

return expression.ToList();

However, if i transform this to use a dynamic where clause (because i want to apply some more filters), the where-clause does not seem to be applied. Instead, all commissions are returned instead of only those with a specific number:

//base query
var expression = from commission in db.Auftraege select new Commission() { EF_Commission = (commission as Auftrag) };

//now add a where clause if the input parameter was specified
if (orderNbr >= 0)
    expression.Where(commission => commission.EF_Commission.Auftragsnummer == orderNbr);

 return expression.ToList();

I have looked at a dozen examples but they all seem to do it this way. Does anybody have an idea why the second query ignores the where clause?

Answer 1

You need to assign the interim expression to something (perhaps to itself). expression.Where() does not alter the existing query – it returns a new one.

So:

expression = expression.Where(...);