SqlDataReader Best way to check for null values -sqlDataReader.IsDBNull vs DBNull.Value

Question

I want to retrieve decimal values from the database and I would like to know which is the recommended way to check for null values.

I have seen on MSDN - DBNull.Value F

Answer 1

I would not get too caught up in the which method is better, because both work and I have used both in code before.

For instance, here is a utility function I dug up from one of my old projects:

/// 

/// Helper class for SqlDataReader, which allows for the calling code to retrieve a value in a generic fashion.
/// 
public static class SqlReaderHelper
{
    private static bool IsNullableType(Type theValueType)
    {
        return (theValueType.IsGenericType && theValueType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)));
    }

    /// 

    /// Returns the value, of type T, from the SqlDataReader, accounting for both generic and non-generic types.
    /// 
    /// T, type applied
    /// The SqlDataReader object that queried the database
    /// The column of data to retrieve a value from
    /// T, type applied; default value of type if database value is null
    public static T GetValue(this SqlDataReader theReader, string theColumnName)
    {
        // Read the value out of the reader by string (column name); returns object
        object theValue = theReader[theColumnName];

        // Cast to the generic type applied to this method (i.e. int?)
        Type theValueType = typeof(T);

        // Check for null value from the database
        if (DBNull.Value != theValue)
        {
            // We have a null, do we have a nullable type for T?
            if (!IsNullableType(theValueType))
            {
                // No, this is not a nullable type so just change the value's type from object to T
                return (T)Convert.ChangeType(theValue, theValueType);
            }
            else
            {
                // Yes, this is a nullable type so change the value's type from object to the underlying type of T
                NullableConverter theNullableConverter = new NullableConverter(theValueType);

                return (T)Convert.ChangeType(theValue, theNullableConverter.UnderlyingType);
            }
        }

        // The value was null in the database, so return the default value for T; this will vary based on what T is (i.e. int has a default of 0)
        return default(T);
    }
}

Usage:

yourSqlReaderObject.GetValue("SOME_ID_COLUMN");
yourSqlReaderObject.GetValue("SOME_VALUE_COLUMN");