Recipe 12.2. Generating XML with the DOM

12.2.1. Problem

You want to generate XML but want to do it in an organized way instead of using print and loops.

12.2.2. Solution

Use the DOM extension to create a DOMDocument object. After building up the document, call DOMDocument::save( ) or DOMDocument::saveXML( ) to generate a well-formed XML document:

<?php // create a new document $dom = new DOMDocument('1.0'); // create the root element, <book>, and append it to the document $book = $dom->appendChild($dom->createElement('book')); // create the title element and append it to $book $title = $book->appendChild($dom->createElement('title')); // set the text and the cover attribute for $title $title->appendChild($dom->createTextNode('PHP Cookbook')); $title->setAttribute('cover', 'soft'); // create and append author elements to $book $sklar = $book->appendChild($dom->createElement('author')); // create and append the text for each element $sklar->appendChild($dom->createTextNode('Sklar')); $trachtenberg = $book->appendChild($dom->createElement('author')); $trachtenberg->appendChild($dom->createTextNode('Trachtenberg')); // print a nicely formatted version of the DOM document as XML $dom->formatOutput = true; echo $dom->saveXML(); ?>

<?xml version="1.0"?> <book>   <title cover="soft">PHP Cookbook</title>   <author>Sklar</author>   <author>Trachtenberg</author> </book>

12.2.3. Discussion

The DOM methods follow a pattern. You create an object as either an element or a text node, add and set any attributes you want, and then append it to the tree in the spot it belongs.

Before creating elements, create a new document, passing the XML version as the sole argument:

$dom = new DOMDocument('1.0');

Now create new elements belonging to the document. Despite being associated with a specific document, nodes don't join the document tree until appended:

$book_element = $dom->createElement('book'); $book = $dom->appendChild($book_element);

Here a new book element is created and assigned to the object $book_element. To create the document root, append $book_element as a child of the $dom document. The result, $book, refers to the specific element and its location within the DOM object.

All nodes are created by calling a method on $dom. Once a node is created, it can be appended to any element in the tree. The element from which we call the appendChild( ) method determines the location in the tree where the node is placed. In the previous case, $book_element is appended to $dom. The element appended to $dom is the top-level node, or the root node.

You can also append a new child element to $book. Since $book is a child of $dom, the new element is, by extension, a grandchild of $dom:

$title_element = $dom->createElement('title'); $title = $book->appendChild($title_element);

By calling $book->appendChild( ), this code places the $title_element element under the $book element.

To add the text inside the <title></title> tags, create a text node using createTextNode( ) and append it to $title:

$text_node = $dom->createTextNode('PHP Cookbook'); $title->appendChild($text_node);

Since $title is already added to the document, there's no need to re-append it to $book.

The order in which you append children to nodes isn't important. The following four lines, which first append the text node to $title_element and then to $book, are equivalent to the previous code:

$title_element = $dom->createElement('title'); $text_node = $dom->createTextNode('PHP Cookbook'); $title_element->appendChild($text_node); $book->appendChild($title_element);

To add an attribute, call setAttribute( ) upon a node, passing the attribute name and value as arguments:

$title->setAttribute('cover', 'soft');

If you print the title element now, it looks like this:

<title cover="soft">PHP Cookbook</title>

Once you're finished, you can output the document as a string or to a file:

// put the string representation of the XML document in $books $books = $dom->saveXML(); // write the XML document to books.xml $dom->save('books.xml');

By default, these methods generate XML output in one long line without any whitespace, including indentations and line breaks. To fix this, set the formatOutput attribute of your DOMDocument to true:

// print a nicely formatted version of the DOM document as XML $dom->formatOutput = true; 

This causes the DOM extension to generate XML like this:

<?xml version="1.0"?> <book>   <title cover="soft">PHP Cookbook</title> </book>

12.2.4. See Also

Recipe 12.1 for writing XML without DOM; Recipe 12.4 for parsing XML with DOM; documentation on DOMDocument at and the DOM functions in general at; more information about the underlying libxml2 C library at

PHP Cookbook, 2nd Edition
PHP Cookbook: Solutions and Examples for PHP Programmers
ISBN: 0596101015
EAN: 2147483647
Year: 2006
Pages: 445

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