How to check a var for null value?

c# .net c#-4.0 .net-4.0 petapoco
RKh picture RKh · May 25, 2012 · Viewed 77k times · Source

I am using PetaPoco Micro-ORM with C# 4.0.

The code below retrieves a single row from the database:

var result = db.SingleOrDefault<TdUsers>(getUserQuery);

I would like to check whether or not the result contains any rows, and whether is null. What is the best way to do this?

Answer

Parv Sharma picture Parv Sharma · May 25, 2012 
if (result == null || result.Count() == 0) {
    // Checks whether the entire result is null OR
    // contains no resulting records.
}

I think the problem is not in your check for null, because linq is lazy loading. Your error is in using the expression db.SingleOrDefault<TdUsers>(getUserQuery);.

.Single<T>(expression) does not return null - it errors if the result returns no values. .SingleOrDefault<T>(expression), however, returns a null value if the expression results in no values - and therefore is best combined with an if (result == null) type check, as you're using here.

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