Instantiate empty IQueryable for use with Linq to sql

Question

I need to be able to either have an optional parameter in a Linq query, or be able to assign the query to a var in something like an IF if that optional parameter needs to be removed from the query.

If I set the query var inside the IF statement then it tells me that the var doesn't exist in context when I try to loop through it.

if (whichGroup == "All")         {             var listOppLineData = (from o in db.opportunity_vws                                    where o.fiscal_yr_and_qtr == qtr                                    select o                                   );         }         else         {             var listOppLineData = (from o in db.opportunity_vws                                    where o.fiscal_yr_and_qtr == qtr && o.Group == whichGroup                                    select o                                   );         }          foreach (var data in listOppLineData)  //listOppLineData doesn't exist here         { 

I need to set the var before the IF statement I think, but I don't know what to set it to.

var listOppLineData = ""; // gives me  Cannot implicitly convert type 'System.Linq.IQueryable<Forecast.Models.opportunity_vw>' to 'string'  IQueryable listOppLineData = new IQueryable(); //gives me         Cannot create an instance of the abstract class or interface 'System.Linq.IQueryable' 

Answer 1

Try this. You can create a generic type with T or a specific type by replacing T with your type name.

IQueryable listOppLineData = Enumerable.Empty<T>().AsQueryable() 

Answer 2

Try this:

IQueryable<opportunity_vw> listOppLineData; 

This is defining the variable, but you are waiting to initialise it.

Also, looking at your query, you could do it all in one, like so:

var listOppLineData = (from o in db.opportunity_vws                       where o.fiscal_yr_and_qtr == qtr && (o.Group == whichGroup || whichGroup == "All")                       select o                       );