Working with XML Nodes

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Once an XML document has been parsed by a DOM implementation, the data it represents is available as a hierarchy of nodes. Each node corresponds to a tagged element in the document. For example, given the following XML:

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!DOCTYPE StockHoldings SYSTEM "sth.dtd">
   <Stock exchange="NASDAQ">
   <Stock exchange="NYSE">
      <shares type="preferred">25</shares>

TXMLDocument would generate a hierarchy of nodes as follows: The root of the hierarchy would be the StockHoldings node. StockHoldings would have two child nodes, which correspond to the two Stock tags. Each of these two child nodes would have four child nodes of its own (name, price, symbol, and shares). Those four child nodes would act as leaf nodes. The text they contain would appear as the value of each of the leaf nodes.

Note: This division into nodes differs slightly from the way a DOM implementation generates nodes for an XML document. In particular, a DOM parser treats all tagged elements as internal nodes. Additional nodes (of type text node) are created for the values of the name, price, symbol, and shares nodes. These text nodes then appear as the children of the name, price, symbol, and shares nodes.

Each node is accessed through an Xml.XMLIntf.IXMLNode interface, starting with the root node, which is the value of the XML document component's DocumentElement property.

Working with a node's value

Given an IXMLNode interface, you can check whether it represents an internal node or a leaf node by checking the IsTextElement property.

  • If it represents a leaf node, you can read or set its value using the Text property.
  • If it represents an internal node, you can access its child nodes using the ChildNodes property.

Thus, for example, using the XML document above, you can read the price of Borland's stock as follows:

BorlandStock := XMLDocument1.DocumentElement.ChildNodes[0];
Price := BorlandStock.ChildNodes['price'].Text;
_di_IXMLNode BorlandStock = XMLDocument1->DocumentElement->ChildNodes->GetNode(0);
AnsiString Price = BorlandStock->ChildNodes->Nodes[WideString("price")]->Text;

Working with the node's attributes

If the node includes any attributes, you can work with them using the Attributes property. You can read or change an attribute value by specifying an existing attribute name. You can add new attributes by specifying a new attribute name when you set the Attributes property:

BorlandStock := XMLDocument1.DocumentElement.ChildNodes[0];
BorlandStock.ChildNodes['shares'].Attributes['type'] := 'common';
_di_IXMLNode BorlandStock = XMLDocument1->DocumentElement->ChildNodes->GetNode(0);
BorlandStock->ChildNodes->Nodes[WideString("shares")]->Attributes[WideString("type")] = "common";

Adding and deleting child nodes

You can add child nodes using the AddChild method. AddChild creates new nodes that correspond to tagged elements in the XML document. Such nodes are called element nodes.

To create a new element node, specify the name that appears in the new tag and, optionally, the position where the new node should appear. For example, the following code adds a new stock listing to the document above:

  NewStock: IXMLNode;
  ValueNode: IXMLNode;
  NewStock := XMLDocument1.DocumentElement.AddChild('stock');
  NewStock.Attributes['exchange'] := 'NASDAQ';
  ValueNode := NewStock.AddChild('name');
  ValueNode.Text := 'Cisco Systems'
  ValueNode := NewStock.AddChild('price');
  ValueNode.Text := '62.375';
  ValueNode := NewStock.AddChild('symbol');
  ValueNode.Text := 'CSCO';
  ValueNode := NewStock.AddChild('shares');
  ValueNode.Text := '25';
_di_IXMLNode NewStock = XMLDocument1->DocumentElement->AddChild(WideString("stock"));
NewStock->Attributes[WideString("exchange")] = "NASDAQ";
_di_IXMLNode ValueNode = NewStock->AddChild(WideString("name"));
ValueNode->Text = WideString("Cisco Systems");
ValueNode = NewStock->AddChild(WideString("price"));
ValueNode->Text = WideString("62.375");
ValueNode = NewStock->AddChild(WideString("symbol"));
ValueNode->Text = WideString("CSCO");
ValueNode = NewStock->AddChild(WideString("shares"));
ValueNode->Text = WideString("25");

An overloaded version of AddChild lets you specify the namespace URI in which the tag name is defined.

You can delete child nodes using the methods of the ChildNodes property. ChildNodes is an IXMLNodeList interface, which manages the children of a node. You can use its Delete method to delete a single child node that is identified by position or by name. For example, the following code deletes the last stock listed in the document above:

StockList := XMLDocument1.DocumentElement;
StockList.ChildNodes.Delete(StockList.ChildNodes.Count - 1);
_di_IXMLNode StockList = XMLDocument1->DocumentElement;
StockList->ChildNodes->Delete(StockList->ChildNodes->Count - 1);

See Also