Creating and Nesting SimpleXMLElement Objects in PHP

Introduction

When working with XML data in PHP, the SimpleXMLElement class provides a convenient way to create and manipulate XML structures. One common requirement is to create a SimpleXMLElement and add it as a child to another SimpleXMLElement. In this blog post, we'll explore the correct solution to achieve this.

Creating the Parent and Child Elements

/* Create the parent SimpleXMLElement */
$parent = new SimpleXMLElement('<parent></parent>');

/* Create the child SimpleXMLElement */
$child = new SimpleXMLElement('<child></child>');

Adding Content to the Child Element

$child->addChild('name', 'John');
$child->addChild('age', 25);

Importing and Nesting the Child Element

Now comes the crucial part: importing and nesting the child element within the parent element. We'll use the dom_import_simplexml() function to convert the SimpleXMLElement objects to DOMNode objects. Here's how it's done:

$domChild = dom_import_simplexml($child);
$domParent = dom_import_simplexml($parent);
$domChild = $domParent->ownerDocument->importNode($domChild, true);
$domParent->appendChild($domChild);

In the above code, we import the child element into the parent element's document using the importNode() method. The second argument true indicates that we want to import the entire subtree of the child node.

Printing the Final XML Structure

To see the final XML structure, we can call the asXML() method on the parent element:

echo $parent->asXML();

This will output the complete XML structure, including the parent and nested child elements.

The xmlAdopt() Method

To simplify the process of adopting a child element into a parent element, we can use a helper method called xmlAdopt():

/**
 * Adopt a SimpleXMLElement into another SimpleXMLElement.
 *
 * @param SimpleXMLElement $parent the parent element
 * @param SimpleXMLElement $child  the child element to add to the parent
 */
private function xmlAdopt(SimpleXMLElement $parent, SimpleXMLElement $child): void
{
    $domChild = dom_import_simplexml($child);
    $domParent = dom_import_simplexml($parent);
    $domChild = $domParent->ownerDocument->importNode($domChild, true);
    $domParent->appendChild($domChild);
}

Using the xmlAdopt() Method:

$this->xmlAdopt($parent, $child);

Conclusion:

Creating and nesting SimpleXMLElement objects in PHP requires careful handling