Data is Null. This method or property cannot be called on Null values

if (!string.IsNullOrEmpty(rd.GetString(2)))
{
    StrBcc =开发者_运维问答 rd.GetString(2);
}

Error: System.Data.SqlTypes.SqlNullValueException: Data is Null. This method or property cannot be called on Null values.

My solution was to create an extension method:

static class DataReaderExtensions
{
    public static string GetStringNullCheck(this IDataReader reader, int ordinal)
    {
        return reader.IsDBNull(ordinal) ? null : reader.GetString(ordinal);
    }
}

So I can use it as:

 StrBcc = rd.GetStringNullCheck(2);

You should use

if (!rd.IsDBNull(2))
    StrBcc = rd.GetString(2);

That's because when you use string.IsNullOrEmpty(x) you are telling your app that x is a string, while is a database null value, which is different from a string whose value is null.

If your values can be NULL then using SqlTypes instead can be a safer solution as they all implement INullable:

StrBcc = rd.GetSqlString(2);

or if you like extension methods:

public static class DataReaderExtensions
{
    public static T GetValueOrNull<T>(this SqlDataReader reader, int ordinal) where T : class
    {
        return !reader.IsDBNull(ordinal) ? reader.GetFieldValue<T>(ordinal) : null;
    }

    public static T? GetValueOrNullable<T>(this SqlDataReader reader,  int ordinal) where T : struct 
    {
        if (reader.IsDBNull(ordinal)) return null;
        return reader.GetFieldValue<T>(ordinal);
    }
}