Question

I’m doing work with LINQ in C#. Part of the code requires a Sum down a column.

SomeTable.Where( CONDITION ).Sum( Entity => Entity.IntColumn );

This returns a type of int? rather than an int as the table’s column’s type is also of the int? form.

My questions are thus:
What is the int? or double? e&. type?
– What is the best practice for converting or casting those types into their useable int or double e&. counter parts?

Answer 1

int?, double?, etc are nullable types. Nullable types can represent all the values of an underlying type, and an additional null value.

Each instance of a nullable type has two public read-only properties:

HasValue
HasValue is of type bool. It is set to true when the variable contains a non-null value.

Value
Value is of the same type as the underlying type. If HasValue is true, Value contains a meaningful value. If HasValue is false, accessing Value will throw a InvalidOperationException.

int? x = 10;
if (x.HasValue)
{
    System.Console.WriteLine(x.Value);
}
else
{
    System.Console.WriteLine("Undefined");
}

http://msdn.microsoft.com/en-us/library/2cf62fcy.aspx#Y431