LINQ to Entities - Checking for a null object

[Joe Campanini]

I'm using LINQ to Entities in a C# program with the following code...

...

var prof = (from p in de.ProfT
            where p.ProfT == ProfTitle
            select p).FirstOrDefault();

if (prof.Title != null)
{

Do some stuff

}

I get a run time exception "Object reference not set to an instance of an object" How do I check if prof.Title not equal to null?

I'm sorry if I'm a bit of a pain with all my questions, believe me I'm not stupid :-D, but I have no other way of learning all this good stuff.

Joe

[Curtis Rutland]

where field.Property != null && field.Property == desiredValue

[Joe Campanini]

Hi Curtis, the problem arises in the "Do some stuff..."

...

nameInfo[1] = prof.Title + " " + name.Firstname + " " + name.Surname;

I get a run time exception "Object reference not set to an instance of an object" on the prof.Title because this particular body does not have a prof.Title

I tried your code but I still get the same error

Joe

[Curtis Rutland]

Hmm, I assumed your error was in your select query.

Anyway, there is an operator that is called the "null coalescing operator". It works like this:

string x = null;
string y = x ?? string.Empty;

That's the equivalent of this:

string x = null;
string y;
if(x == null)
  y = string.Empty;
else 
  y = x;

What it does: use the provided value only if it is not null. Otherwise, it uses the replacement value (on the right of the ??).

So you could conceivably do something like this:

nameInfo[1] = prof.Title ?? string.Empty + " " + name.Firstname ?? string.Empty+ " " + name.Surname ?? string.Empty;

Though I wouldn't suggest it. I wouldn't build the string like that. I'd use a StringBuilder:

using System.Text;
...
StringBuilder sb = new StringBuilder();
if(!string.IsNullOrWhiteSpace(myString1))
  sb.Append(string1 + " ");
if(!string.IsNullOrWhiteSpace(myString2))
  sb.Append(string2 + " ");
if(!string.IsNullOrWhiteSpace(myString3))
  sb.Append(string3 + " ");

That way, you're not adding the spaces whether or not the strings are null. Only if they exist (and aren't empty).

[Joe Campanini]

Thanks Curtis, youre a genius, I haven't even heard of a StringBuilder, :-D, I learn something new everyday. But I have been adviced that whatever it is you want to do there is a class out there somewhere that will do it, and it's proving, so far, to be true. Once again thanks. How long have you been doing this stuff??

Joe

[Curtis Rutland]

C# for a few years now, but programming for about 10 years.