First of all, beware of finding old examples. You've found one that uses XmlTextWriter, which is deprecated as of .NET 2.0. XmlWriter.Create should be used instead.
Here's an example of serializing an object into an XML column:
public void SerializeToXmlColumn(object obj)
{
using (var outputStream = new MemoryStream())
{
using (var writer = XmlWriter.Create(outputStream))
{
var serializer = new XmlSerializer(obj.GetType());
serializer.Serialize(writer, obj);
}
outputStream.Position = 0;
using (var conn = new SqlConnection(Settings.Default.ConnectionString))
{
conn.Open();
const string INSERT_COMMAND = @"INSERT INTO XmlStore (Data) VALUES (@Data)";
using (var cmd = new SqlCommand(INSERT_COMMAND, conn))
{
using (var reader = XmlReader.Create(outputStream))
{
var xml = new SqlXml(reader);
cmd.Parameters.Clear();
cmd.Parameters.AddWithValue("@Data", xml);
cmd.ExecuteNonQuery();
}
}
}
}
}