Question

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 1

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.