Code Listings

Chapter 11: Other XML Technologies

Enumerating nodes with XmlReader:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<customer id="123" status="archived">
  <firstname>Jim</firstname>
  <lastname>Bo</lastname>
</customer>

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;

using (XmlReader reader = XmlReader.Create ("customer.xml", settings))
  while (reader.Read())
  {
    Console.Write (new string (' ',reader.Depth*2));  // Write indentation
    Console.WriteLine (reader.NodeType);
  }

Processing XNodeType:

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE customer [ <!ENTITY tc "Top Customer"> ]>
<customer id="123" status="archived">
  <firstname>Jim</firstname>
  <lastname>Bo</lastname>
  <quote><![CDATA[C#'s operators include: < > &]]></quote>
  <notes>Jim Bo is a &tc;</notes>
  <!--  That wasn't so bad! -->
</customer>

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;
settings.ProhibitDtd = false;      // Must set this to read DTDs

using (XmlReader r = XmlReader.Create ("customer.xml", settings))
  while (r.Read())
  {
    Console.Write (r.NodeType.ToString().PadRight (17, '-'));
    Console.Write ("> ".PadRight (r.Depth * 3));

    switch (r.NodeType)
    {
      case XmlNodeType.Element:
      case XmlNodeType.EndElement:
        Console.WriteLine (r.Name); break;

      case XmlNodeType.Text:
      case XmlNodeType.CDATA:
      case XmlNodeType.Comment:
      case XmlNodeType.XmlDeclaration:
        Console.WriteLine (r.Value); break;

      case XmlNodeType.DocumentType:
        Console.WriteLine (r.Name + " - " + r.Value); break;

      default: break;
    }
  }

Using ReadElementContentAs:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<customer id="123" status="archived">
  <firstname>Jim</firstname>
  <lastname>Bo</lastname>
  <creditlimit>500.00</creditlimit>    <!-- OK, we sneaked this in! -->
</customer>

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;

using (XmlReader r = XmlReader.Create ("customer.xml", settings))
{
  r.MoveToContent();                // Skip over the XML declaration
  r.ReadStartElement ("customer");
  string firstName    = r.ReadElementContentAsString ("firstname", "");
  string lastName     = r.ReadElementContentAsString ("lastname", "");
  decimal creditLimit = r.ReadElementContentAsDecimal ("creditlimit", "");

  r.MoveToContent();      // Skip over that pesky comment
  r.ReadEndElement();     // Read the closing customer tag
}

Optional elements:

r.ReadStartElement ("customer");
string firstName    = r. ReadElementContentAsString ("firstname", "");
string lastName     = r.Name == "lastname"
                      ? r.ReadElementContentAsString() : null;
decimal creditLimit = r.ReadElementContentAsDecimal ("creditlimit", "");

Checking for an empty element:

bool isEmpty = reader.IsEmptyElement;
reader.ReadStartElement ("customerList");
if (!isEmpty) reader.ReadEndElement();

Reading attributes:

<customer id="123" status="archived"/>

Console.WriteLine (reader ["id"]);              // 123
Console.WriteLine (reader ["status"]);          // archived
Console.WriteLine (reader ["bogus"] == null);   // True

Console.WriteLine (reader [0]);            // 123
Console.WriteLine (reader [1]);            // archived

reader.MoveToAttribute ("status");
string status = ReadContentAsString();

reader.MoveToAttribute ("id");
int id = ReadContentAsInt();

if (reader.MoveToFirstAttribute())
  do
  {
    Console.WriteLine (reader.Name + "=" + reader.Value);
  }
  while (reader.MoveToNextAttribute());

// OUTPUT:
id=123
status=archived

XmlWriter:

XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;

using (XmlWriter writer = XmlWriter.Create ("..\\..\\foo.xml", settings))
{
  writer.WriteStartElement ("customer");
  writer.WriteElementString ("firstname", "Jim");
  writer.WriteElementString ("lastname"," Bo");
  writer.WriteEndElement();
}

Writing attributes:

writer.WriteStartElement ("customer");
writer.WriteAttributeString ("id", "1");
writer.WriteAttributeString ("status", "archived");

Namespaces and prefixes:

writer.WriteStartElement ("o", "customer", "http://oreilly.com");
writer.WriteElementString ("o", "firstname", "http://oreilly.com", "Jim");
writer.WriteElementString ("o", "firstname", "http://oreilly.com", "Bo");
writer.WriteEndElement();

Working with hierarchical data:

public class Customer 
{
  public const string XmlName = "customer";
  public int? ID;
  public string FirstName, LastName;

  public Customer() { }
  public Customer (XmlReader r) { ReadXml (r); }

  public void ReadXml (XmlReader r)
  {
    if (r.MoveToAttribute ("id")) ID = r.ReadContentAsInt();
    r.ReadStartElement();
    FirstName = r.ReadElementContentAsString ("firstname", "");
    LastName = r.ReadElementContentAsString ("lastname", "");
    r.ReadEndElement();
  }

  public void WriteXml (XmlWriter w)
  {
    if (ID.HasValue) w.WriteAttributeString ("id", "", ID.ToString());
    w.WriteElementString ("firstname", FirstName);
    w.WriteElementString ("lastname", LastName);
  }
}

public class Supplier 
{
  public const string XmlName = "supplier";
  public string Name;

  public Supplier() { }
  public Supplier (XmlReader r) { ReadXml (r); }

  public void ReadXml (XmlReader r)
  {
    r.ReadStartElement();
    Name = r.ReadElementContentAsString ("name", "");
    r.ReadEndElement();
  }

  public void WriteXml (XmlWriter w)
  {
    w.WriteElementString ("name", Name);
  }
}

public class Contacts
{
  public IList<Customer> Customers = new List<Customer>();
  public IList<Supplier> Suppliers = new List<Supplier>();

  public void ReadXml (XmlReader r)
  {
    bool isEmpty = r.IsEmptyElement;           // This ensures we don't get
    r.ReadStartElement();                      // snookered by an empty
    if (isEmpty) return;                       // <contacts/> element!
    while (r.NodeType == XmlNodeType.Element)
    {
      if (r.Name == Customer.XmlName)      Customers.Add (new Customer (r));
      else if (r.Name == Supplier.XmlName) Suppliers.Add (new Supplier (r));
      else
        throw new XmlException ("Unexpected node: " + r.Name);
    }
    r.ReadEndElement();
  }

  public void WriteXml (XmlWriter w)
  {
    foreach (Customer c in Customers)
    {
      w.WriteStartElement (Customer.XmlName);
      c.WriteXml (w);
      w.WriteEndElement();
    }
    foreach (Supplier s in Suppliers)
    {
      w.WriteStartElement (Supplier.XmlName);
      s.WriteXml (w);
      w.WriteEndElement();
    }
  }
}

Using XmlReader with XElement:

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;

using (XmlReader r = XmlReader.Create ("logfile.xml", settings))
{
  r.ReadStartElement ("log");
  while (r.Name == "logentry")
  {
    XElement logEntry = (XElement) XNode.ReadFrom (r);
    int id = (int) logEntry.Attribute ("id");
    DateTime date = (DateTime) logEntry.Element ("date");
    string source = (string) logEntry.Element ("source");
    ...
  }
  r.ReadEndElement();
}

Using XmlWriter with XElement:

using (XmlWriter w = XmlWriter.Create ("log.xml"))
{
  w.WriteStartElement ("log");
  for (int i = 0; i < 1000000; i++)
  {
    XElement e = new XElement ("logentry",
                   new XAttribute ("id", i),
                   new XElement ("date", DateTime.Today.AddDays (-1)),
                   new XElement ("source", "test"));
    e.WriteTo (w);
  }
  w.WriteEndElement();
}

Creating an XmlDocument:

XmlDocument doc = new XmlDocument();
doc.AppendChild (doc.CreateXmlDeclaration ("1.0", null, "yes"));

XmlAttribute id     = doc.CreateAttribute ("id");
XmlAttribute status = doc.CreateAttribute ("status");
id.Value     = "123";
status.Value = "archived";

XmlElement firstname = doc.CreateElement ("firstname");
XmlElement lastname  = doc.CreateElement ("lastname");
firstname.AppendChild (doc.CreateTextNode ("Jim"));
lastname.AppendChild  (doc.CreateTextNode ("Bo"));

XmlElement customer = doc.CreateElement ("customer");
customer.Attributes.Append (id);
customer.Attributes.Append (status);
customer.AppendChild (lastname);
customer.AppendChild (firstname);

doc.AppendChild (customer);

XPath:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<customers>
  <customer id="123" status="archived">
    <firstname>Jim</firstname>
    <lastname>Bo</lastname>
  </customer>
  <customer>
    <firstname>Thomas</firstname>
    <lastname>Jefferson</lastname>
  </customer>
</customers>

XmlDocument doc = new XmlDocument();
doc.Load ("customers.xml");
XmlNode n = doc.SelectSingleNode ("customers/customer[firstname='Jim']");
Console.WriteLine (n.InnerText);  // JimBo

XDocument doc = XDocument.Load (@"Customers.xml");
XElement e = e.XPathSelectElement ("customers/customer[firstname='Jim']");
Console.WriteLine (e.Value);  // JimBo

XmlNode node1 = doc.SelectSingleNode ("customers");
XmlNode node2 = doc.SelectSingleNode ("customers/customer");
XmlNodeList nodes3 = doc.SelectNodes ("//lastname");
XmlNodeList nodes4 = doc.SelectNodes ("customers/customer..customers");
XmlNodeList nodes5 = doc.SelectNodes ("customers/customer/*");
XmlNode node6 = doc.SelectSingleNode ("customers/customer/@id");
XmlNode node7 = doc.SelectSingleNode ("customers/customer[firstname='Jim']");
XmlNode node8 = doc.SelectSingleNode ("x:customers");

XPathNavigator:

XPathNavigator nav = doc.CreateNavigator();
XPathNavigator jim = nav.SelectSingleNode
  (
    "customers/customer[firstname='Jim']"
  );

Console.WriteLine (jim.Value);                    // JimBo

Using Select:

XPathNavigator nav = doc.CreateNavigator();
string xPath = "customers/customer/firstname/text()";
foreach (XPathNavigator navC in nav.Select (xPath))
  Console.WriteLine (navC.Value);

Compiling an XPath query:

XPathNavigator nav = doc.CreateNavigator();
XPathExpression expr = nav.Compile ("customers/customer/firstname");
foreach (XPathNavigator a in nav.Select (expr))
  Console.WriteLine (a.Value);

Querying with namespaces:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>

<o:customers xmlns:o='http://oreilly.com'>
  <o:customer id="123" status="archived">
    <firstname>Jim</firstname>
    <lastname>Bo</lastname>
  </o:customer>
  <o:customer>
    <firstname>Thomas</firstname>
    <lastname>Jefferson</lastname>
  </o:customer>
</o:customers>

XmlDocument doc = new XmlDocument();
doc.Load ("customers.xml");

XmlNamespaceManager xnm = new XmlNamespaceManager (doc.NameTable);
xnm.AddNamespace ("o", "http://oreilly.com");

XmlNode n = doc.SelectSingleNode ("o:customers/o:customer", xnm);

XPathDocument:

XPathDocument doc = new XPathDocument ("customers.xml");
XPathNavigator nav = doc.CreateNavigator();
foreach (XPathNavigator a in nav.Select ("customers/customer/firstname"))
  Console.WriteLine (a.Value);

XSD and schema validation:

<?xml version="1.0"?>
<customers>
  <customer id="1" status="active">
    <firstname>Jim</firstname>
    <lastname>Bo</lastname>
  </customer>
  <customer id="1" status="archived">
    <firstname>Thomas</firstname>
    <lastname>Jefferson</lastname>
  </customer>
</customers>

<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified"
           elementFormDefault="qualified"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="customers">
    <xs:complexType>
      <xs:sequence>
        <xs:element maxOccurs="unbounded" name="customer">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="firstname" type="xs:string" />
              <xs:element name="lastname" type="xs:string" />
            </xs:sequence>
            <xs:attribute name="id" type="xs:int" use="required" />
            <xs:attribute name="status" type="xs:string" use="required" />
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

Validating with an XmlReader:

XmlReaderSettings settings = new XmlReaderSettings();
settings.ValidationType = ValidationType.Schema;
settings.Schemas.Add (null, "customers.xsd");

using (XmlReader r = XmlReader.Create ("customers.xml", settings))
  try { while (r.Read()) ; }
  catch (XmlSchemaValidationException ex)
  {
    ...
  }

Using ValidationEventHandler:

XmlReaderSettings settings = new XmlReaderSettings();
settings.ValidationType = ValidationType.Schema;
settings.Schemas.Add (null, "customers.xsd");
settings.ValidationEventHandler += ValidationHandler;

using (XmlReader r = XmlReader.Create ("customers.xml", settings))
  while (r.Read()) ;

static void ValidationHandler (object sender, ValidationEventArgs e)
{
  Console.WriteLine ("Error: " + e.Exception.Message);
}

Validating an X-DOM or XmlDocument:

XmlReaderSettings settings = new XmlReaderSettings();
settings.ValidationType = ValidationType.Schema;
settings.Schemas.Add (null, "customers.xsd");

XDocument doc;
using (XmlReader r = XmlReader.Create ("customers.xml", settings))
  try { doc = XDocument.Load (r); }
  catch (XmlSchemaValidationException ex) { ... }

XmlDocument xmlDoc = new XmlDocument();
using (XmlReader r = XmlReader.Create ("customers.xml", settings))
  try { xmlDoc.Load (r); }
  catch (XmlSchemaValidationException ex) { ... }

XDocument doc = XDocument.Load (@"customers.xml");
XmlSchemaSet set = new XmlSchemaSet();
set.Add (null, @"customers.xsd");
StringBuilder errors = new StringBuilder();
doc.Validate (set, (sender, args) => { errors.AppendLine
                                       (args.Exception.Message); }
             );
Console.WriteLine (errors.ToString());

XSLT:

<customer>
  <firstname>Jim</firstname>
  <lastname>Bo</lastname>
</customer>

<?xml version="1.0" encoding="UTF-8"?>
  <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:template match="/">
    <html>
      <p><xsl:value-of select="//firstname"/></p>
      <p><xsl:value-of select="//lastname"/></p>
    </html>
  </xsl:template>
</xsl:stylesheet>

XslCompiledTransform transform = new XslCompiledTransform();
transform.Load ("test.xslt");
transform.Transform ("input.xml", "output.xml");