SqlDataReader ve null gelen veri sorununa prait çözümler. Çözüm 1: SqlDataReader için generic extension olusturulur. Çözüm 2: de bir static fonksiyon olusturulur. Bu fonksiyon null ile default değeri gönderir yoksa convert ederek verir.Convert.ToInt32() yerine düşünün. Çözüm 3: c# ?? operatörü.

Çözüm 1

//Kaynak: http://stackoverflow.com/questions/18550769/sqldatareader-best-way-to-check-for-null-values-sqldatareader-isdbnull-vs-dbnul


using System;
using System.ComponentModel;
using System.Data.SqlClient;

public static class SqlReaderHelper
{
    private static bool IsNullableType(Type theValueType)
    {
        return (theValueType.IsGenericType && theValueType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)));
    }

    /// <summary>
    /// Returns the value, of type T, from the SqlDataReader, accounting for both generic and non-generic types.
    /// </summary>
    /// <typeparam name="T">T, type applied</typeparam>
    /// <param name="theReader">The SqlDataReader object that queried the database</param>
    /// <param name="theColumnName">The column of data to retrieve a value from</param>
    /// <returns>T, type applied; default value of type if database value is null</returns>
    public static T GetValue<T>(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);
    }
}

//yourSqlReaderObject.GetValue<int?>("SOME_ID_COLUMN");
//yourSqlReaderObject.GetValue<string>("SOME_VALUE_COLUMN");
//Diyerek de kullanabiliriz.

Çözüm 2

//Kaynak: http://stackoverflow.com/questions/17509144/how-to-get-null-values-in-sqldatareader
private static T GetValue<T>(object value)
{
    return value == DBNull.Value
           ? default(T)
           : (T) Convert.ChangeType(value, typeof(T));
}

// s.id       = GetValue<long>(reader["so_id"]);
// s.senderid = GetValue<long>(reader["so_senderid"]);
// Diyerek de bunu kullanabilrisiniz. 

Çözüm 3

//Kaynak: http://msdn.microsoft.com/en-us/library/ms173224.aspx

int? x = null;

// Set y to the value of x if x is NOT null; otherwise, 
// if x = null, set y to -1. 
int y = x ?? -1;