SQL Data Reader - handling Null column values

Question

I\'m using a SQLdatareader to build POCOs from a database. The code works except when it encounters a null value in the database. For example, if the FirstName column in the

Answer 1

how to about creating helper methods

For String

private static string MyStringConverter(object o)
    {
        if (o == DBNull.Value || o == null)
            return "";

        return o.ToString();
    }

Usage

MyStringConverter(read["indexStringValue"])

For Int

 private static int MyIntonverter(object o)
    {
        if (o == DBNull.Value || o == null)
            return 0;

        return Convert.ToInt32(o);
    }

Usage

MyIntonverter(read["indexIntValue"])

For Date

private static DateTime? MyDateConverter(object o)
    {
        return (o == DBNull.Value || o == null) ? (DateTime?)null : Convert.ToDateTime(o);
    }

Usage

MyDateConverter(read["indexDateValue"])

Note: for DateTime declare varialbe as

DateTime? variable;

Answer 2

IsDbNull(int) is usually much slower than using methods like GetSqlDateTime and then comparing to DBNull.Value. Try these extension methods for SqlDataReader.

public static T Def<T>(this SqlDataReader r, int ord)
{
    var t = r.GetSqlValue(ord);
    if (t == DBNull.Value) return default(T);
    return ((INullable)t).IsNull ? default(T) : (T)t;
}

public static T? Val<T>(this SqlDataReader r, int ord) where T:struct
{
    var t = r.GetSqlValue(ord);
    if (t == DBNull.Value) return null;
    return ((INullable)t).IsNull ? (T?)null : (T)t;
}

public static T Ref<T>(this SqlDataReader r, int ord) where T : class
{
    var t = r.GetSqlValue(ord);
    if (t == DBNull.Value) return null;
    return ((INullable)t).IsNull ? null : (T)t;
}

Use them like this:

var dd = r.Val<DateTime>(ords[4]);
var ii = r.Def<int>(ords[0]);
int nn = r.Def<int>(ords[0]);

Answer 3

reader.IsDbNull(ColumnIndex) works as many answers says.

And I want to mention if you working with column names, just comparing types may be more comfortable.

if(reader["TeacherImage"].GetType() == typeof(DBNull)) { //logic }

Answer 4

and / or use ternary operator with assignment:

employee.FirstName = rdr.IsDBNull(indexFirstName))? 
                     String.Empty: rdr.GetString(indexFirstName);

replace the default (when null) value as appropriate for each property type...

Answer 5

As an addition to the answer by marc_s, you can use a more generic extension method to get values from the SqlDataReader:

public static T SafeGet<T>(this SqlDataReader reader, int col)
    {
        return reader.IsDBNull(col) ? default(T) : reader.GetFieldValue<T>(col);
    }

Answer 6

By influencing from getpsyched's answer, I created a generic method which checks column value by its name

public static T SafeGet<T>(this System.Data.SqlClient.SqlDataReader reader, string nameOfColumn)
{
  var indexOfColumn = reader.GetOrdinal(nameOfColumn);
  return reader.IsDBNull(indexOfColumn) ? default(T) : reader.GetFieldValue<T>(indexOfColumn);
}

Usage:

var myVariable = SafeGet<string>(reader, "NameOfColumn")