Modifying and saving an XML file in Drupal

3 min readJun 3, 2021

Today's use case is to alter content of an existing XML file in my public files directory when a user triggers an add forms save action.

For this to work we need to implement a hook_form_FORM_ID_alter

Let's say the node type the user is editing is called My Files and below is the form display.

The task is to

Modify an attribute called guid by concatenating publication date.
Add a new attribute called id in to schedules element

The original XML file content looks like this

<?xml version="1.0" encoding="utf-8"?>
<act title="Act 2009" id="act-2009-017" publication.date="2022-05-23">
  <coverdata id="cd" guid="_f2e529dd-a9f3-434d-bb84-36748dbe2505"/>
  <wrapper>
    <front id="frnt" guid="_2ce2d477-94b7-4f8f-9d16-80ea92e096a4">
      <shorttitle id="frnt-st" guid="_927cc402-5436-40b3-a2da-1f620c45ef1e">Act 2009</shorttitle>
      <longtitle id="frnt-lt" guid="_4bbf8fc9-b3b1-4805-bb91-7b4a16304045">
        <block>
          <txt break.before="1">Some Text</txt>
        </block>
      </longtitle>
    </front>
  </wrapper>
  <schedules numbering.style="manual" affected.by.uncommenced="0">
    <schedule id="sch.1" guid="_42855c73-aa10-47c4-b9ce-3a77d34c9607"></schedule>
  </schedules>
</act>

To tap into this form you will need to find its form ID. You can either find it by inspecting the element via web browser or by placing a breakpoint inside hook_form_alter

In this scenario the form alter code needs to be placed into the modules .module file. My custom module name is xml_migrate, hence the file name will be xml_example.module

Using inspect element, I’ve found the form name to be as node_xml_file_form.

/**
 * Alter XML File ADD form to modify the XML content.
 *
 * Implements hook_form_FORM_ID_alter().
 */
function xml_migrate_form_node_xml_file_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  $form['actions']['submit']['#submit'][] = 'xml_migrate_update_xml_file_submit'; //This will be the callback function name
  return $form;
}

The above code will add a new action to the submit button and the callback function is called xml_migrate_update_xml_file_submit. We will add our logic there.

/**
 * Custom submit callback to rename all guid attributes by concatenating with
 * published date.
 * And add ID attribute for schedules.
 */
function xml_migrate_update_xml_file_submit(&$form, FormStateInterface $form_state) {// Helper class have a constant that holds the path name of the file upload directory
  $helper = new Helper(); // field_xml_file is the file upload field name in the node
  $fid = $form_state->getValue('field_xml_file')[0]['fids'][0];   $file = File::load($fid); 
  $file_name = $file->getFilename();
  $file_path = $helper::XML_FOLDER . '/' . $file_name;// Converts the XML content to a SimpleXML object.
  $xmlObject = simplexml_load_file($file_path);// Use xpath to target the publication.date attribute  $published_date = $xmlObject->xpath('/node()[self::subordleg or self::act]')[0]->attributes()['publication.date'];// Use xpath to target the id attribute
$legislation_id = $xmlObject->xpath('/node()[self::subordleg or self::act]')[0]->attributes()['id'];// Find the schedules element and set new attribute called id if it do not exist.  if (!isset($xmlObject->xpath('//node()[self::schedules]')[0]->attributes()->id)) {
    $xmlObject->xpath('//node()[self::schedules]')[0]->addAttribute("id", $legislation_id . '_' . $published_date);
  }// Update all the guid values throughout the document foreach ($xmlObject->xpath('//@guid') as $item) {
    $item->guid = $item->guid . '_' . $published_date;
  }// Save the updated object to a new file. In this case I'm overwriting existing file.
  $xmlObject->asXML($file_path);
}

And that's it ! We have successfully updated the XML file.

Modifying and saving an XML file in Drupal

Written by Pasan Gamage