C# check for null in linq

14y3.4kVisual Basic .NET

For a C# 2010 application, I would like to be able to check for the value
returned by the linq to sql query listed below as being null.
Is there any way to check for

strOrgName == null?

string strOrgName = (from o in rData.Orgs
                  join pl in rData.Custs on o.OrgID equals pl.OrgID
                  where pl.orgnum == strContract
                  select o.OrgName).FirstOrDefault();

The code I have written so far only allows if I check for
strOrgName != null.

I am using the code above to use as an example of how I would like to be able
check for the value returned being a null.

Thus can you tell me how to solve my isuse?

4 Replies

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Vulpes14y ago
Accepted answer
When the 'var' keyword is used in a local variable declaration, it's an instruction to the C# compiler to infer the type of the variable from the type of the expression which is being assigned to it.

So, for example:

var s = "abc";

is precisely equivalent to:

string s = "abc";

and:

var i = 3;

is precisely equivalent to:

int i = 3;

Also 'var' is strongly typed so you're not allowed to do this:

s = 5; // error because s is a string variable

The only times when the expression assigned to a 'var' variable can be null are where the type of the expression is:

1. A reference type such as string, object etc.

2. A nullable value type such as int?, double? etc.

So, if you try to test such a variable for nullness, you'll get a compiler error for a non-nullable value type (int, bool etc), which can't be null, but not for #1 and #2 above.

It looks to me like the LINQ expression returns a string (i.e. the type of o.OrgName) and so strOrgName is (as its name suggests) a string variable.

If that's the case, then you shouldn't get a compiler error when you do this:

if (strOrgName == null)
{
// do something
}

so I'm puzzled why you are, which is the implication of your question?
Shivanand Arur14y ago
Yes, Vulpes ais absolutely right.... You can check the nullness in...

if(strOrgName == null)
{
// Your Code here
}

or

if(String.IsNullOrEmpty(strOrgName))
{
//Your Code here.
}
dc14y ago
Most of the time, I use a var value like the following statement:

var strOrgName = (from o in rData.Orgs
                  join pl in rData.Custs on o.OrgID equals pl.OrgID
                  where pl.orgnum == strContract
                  select o.OrgName).FirstOrDefault();

How can I check for a null value in a 'var' declared field? I would like to say if

if strOrgName == null and not get a compile error?

Should I convert the var value to a string or int? How would you procede?
Shivanand Arur14y ago
After getting the value in the string... you can check whether it is null or empty in this way...

if(!String.IsNullOrEmpty( strOrgName))
{
// Add your Logic 1
}
else
{
// Add your Logic 2
}

I hope this is what you wanted.... If not, then please post your question again... Thank you.