How to Read and Write XML Documents using PHP DOM Extension

Background

With XML Parser, you use can only read XML. To write and otherwise manipulate an XML document, you can use PHP DOM Extension. DOM stands for Document Object Model and it is a way of expressing XML nodes as a hierarchical tree of objects.

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An XML document is read into memory as a tree of objects. Unlike with the XML Parser extension, the PHP DOM extension can traverse the tree in any directions to explore various elements, attributes, text nodes, and other nodes in the XML.  Nodes can be modified too.

Software Requirements

• Windows 7 Professional SP1
• PHP 5.5.9 / Zend Engine v2.5.0
• NetBeans IDE 8.0.1
• ApacheFriends XAMPP Version 1.8.3
  • ​Apache/2.4.7 (Win32) / Open SSL/1.0.1e

DOM Classes

Using DOM involves working with several built-in classes. The most common ones are the following:

1. DOMNode
   This represents a single node in the DOM tree. Most DOM classes derive from DOMNode class.
2. DOMDocument
   This represents the entire XML document in the form of a DOM tree stored in the memory. It derives from DMNode class, and is, the root of the tree.
3. DOMElement
   This represents an element node.
4. DOMAttr
   This represents an element’s attribute.
5. DOMText
   This represents a plain-text node.
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6. DOMCharacterData
   This represents a CDATA (character data) node.

Working with DOM

Reading XML

The basic steps for reading XML documents are as follow:

1. Create a DOMDocument object
   
   PHP

   $payment_transaction = new DOMDocument();

   1	$payment_transaction = new DOMDocument();

2. Read an XML String or load an XML file
   
   PHP

   // Read an XML String $payment_transaction->loadXML($XML_string); // load XML from file $payment_transaction->loadXML('trx01.xml');

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   // Read an XML String $payment_transaction->loadXML($XML_string);   // load XML from file $payment_transaction->loadXML('trx01.xml');

3. Traverse the content of the DOMDocument object using DOM-related properties and functions
   
   PHP

   function displayXMLDocument($node) { switch ( $node->nodeType ) { case XML_ELEMENT_NODE: echo "Found element: $node->tagName"; if($node->hasAttributes()) { echo " with attributes: \n"; } foreach($node->attributes as $attribute ) { echo "$attribute->name = $attribute->value\n"; } break; case XML_CDATA_SECTION_NODE: if ( trim($node->data) ) { echo "Found character data node: " . htmlspecialchars($node->data) . "\n"; } break; case XML_TEXT_NODE: if(trim($node->wholeText)) { echo "Found text node: $node->wholeText\n"; } break; } if($node->hasChildNodes()) { foreach ($node->childNodes as $child ) { displayXMLDocument($child); } } } // Pass the DOMDocument object to this user-defined function displayXMLDocument($payment_transaction);

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   function displayXMLDocument($node) {     switch ( $node->nodeType ) {         case XML_ELEMENT_NODE:             echo "Found element: $node->tagName";             if($node->hasAttributes()) {                 echo " with attributes: \n";             }                          foreach($node->attributes as $attribute ) {                 echo "$attribute->name = $attribute->value\n";             }             break;                      case XML_CDATA_SECTION_NODE:             if ( trim($node->data) ) {                 echo "Found character data node: " . htmlspecialchars($node->data) . "\n";             }             break;                      case XML_TEXT_NODE:             if(trim($node->wholeText)) {                 echo "Found text node: $node->wholeText\n";             }             break;     }     if($node->hasChildNodes()) {         foreach ($node->childNodes as $child ) {             displayXMLDocument($child);         }     } }   // Pass the DOMDocument object to this user-defined function displayXMLDocument($payment_transaction);

Creating an XML Document

The basic steps for creating an XML document are as follow:

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1. Create an object of DOMDocument
   
   PHP

   $new_payment_transaction = new DOMDocument("1.0", "UTF-8"); $new_payment_transaction ->formatOutput = true;

   1 2	$new_payment_transaction = new DOMDocument("1.0", "UTF-8"); $new_payment_transaction ->formatOutput = true;

2. Build up the document
   
   PHP

   $new_payment_transaction = new DOMDocument("1.0", "UTF-8"); $new_payment_transaction->formatOutput = true; // Create the root "payment" element $payment_root = $new_payment_transaction->createElement("payment"); $new_payment_transaction->appendChild($payment_root); // Create the first "account" $account = $new_payment_transaction->createElement("account"); $account->setAttribute("id", "0123456789"); $account->setAttribute("type", "nonmember"); $payment_root->appendChild($account); // Create the account’s "payment-details" child element $payment_details = $new_payment_transaction->createElement("amount", "100"); $account->appendChild( $payment_details );

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   $new_payment_transaction = new DOMDocument("1.0", "UTF-8"); $new_payment_transaction->formatOutput = true; // Create the root "payment" element $payment_root = $new_payment_transaction->createElement("payment"); $new_payment_transaction->appendChild($payment_root); // Create the first "account" $account = $new_payment_transaction->createElement("account"); $account->setAttribute("id", "0123456789"); $account->setAttribute("type", "nonmember");   $payment_root->appendChild($account); // Create the account’s "payment-details" child element $payment_details = $new_payment_transaction->createElement("amount", "100"); $account->appendChild( $payment_details );

3. Save or print the content of the XML document
   
   PHP

   echo $new_payment_transaction->saveXML($new_payment_transaction->documentElement); // or save to file $new_payment_transaction->save('new_payment.xml');

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   echo $new_payment_transaction->saveXML($new_payment_transaction->documentElement);   // or save to file   $new_payment_transaction->save('new_payment.xml');

Sample Output