debugging - How to debug a LINQ Statement

Question

I have a Linq to objects statement

 var confirm = from l in lines.Lines 
 where (l.LineNumber == startline.LineNumber) || (l.LineNumber == endline.LineNumber) 
 select l;

The confirm object is returning an 'Object Null or Not A Reference' at at System.Linq.Enumerable.WhereListIterator`1.MoveNext()

If the result of the query was empty, it would just return an empty enumerator. I know for a fact that there are no null objects in the statement. Is it possible to step through the LINQ statement to see where it is falling over?

EDIT When I said I know for a fact that there are no null objects it turns out I was lying :[, but the question remains, though I am asuming the answer will be 'you can't really'

LINQPad is a good idea, I used it to teach myself LINQ, but I may start looking at it again as a debug / slash and burn style tool

Answer 1

Yes it is indeed possible to pause execution midway through a linq query.

Convert your linq to query style using lambda expressions and insert a Select statement that returns itself somewhere after the point in the linq that you want to debug. Some sample code will make it clearer -

        var query = dataset.Tables[0].AsEnumerable()
            .Where (i=> i.Field<string>("Project").Contains("070932.01"))
 //         .Select(i =>
 //         {return i;}
 //           )
            .Select (i=>i.Field<string>("City"));

Then uncomment the commented lines. Make sure the {return i;} is on its own line and insert a debug point there. You can put this select at any point in your long, complicated linq query.