Question

Why does this work:

result = (from e in db.CampaignCodes where e.Code.Equals('') &&  e.Domain.Equals(null) select e).FirstOrDefault(); 

But not (result is null):

String code = ''; String domain = null;  result = (from e in db.CampaignCodes where e.Code.Equals(code) &&  e.Domain.Equals(domain) select e).FirstOrDefault(); 

??

Answer 1

That does indeed sound quite odd. LINQ to SQL may well notice the difference between getting the value from a variable and getting it from a constant, but I wouldn’t have expected it to make any difference.

I strongly recommend that whenever LINQ to SQL appears to be behaving oddly, you turn the context logging on and see what query it’s actually executing in each case.

EDIT: The other answers around the overloading aspect are really interesting. What happens if you declare the domain variable as type object instead of string in the second query, or cast the null to string in the first query?