silverstripe-framework/tests/php/ORM/DataExtensionTest/CMSFieldsGrandChild.php

<?php

namespace SilverStripe\ORM\Tests\DataExtensionTest;

use SilverStripe\Dev\TestOnly;
use SilverStripe\Forms\FieldList;
use SilverStripe\Forms\TextField;
use SilverStripe\ORM\Tests\DataExtensionTest\CMSFieldsChild;

/**
 * Third level test class, testing that beforeExtendingCMSFields can be nested
 */
class CMSFieldsGrandChild extends CMSFieldsChild implements TestOnly
{
	private static $table_name = 'DataExtensionTest_CMSFieldsGrandChild';

	private static $db = array(
		'GrandchildField' => 'Varchar(255)'
	);

	public function getCMSFields()
	{
		$this->beforeUpdateCMSFields(function (FieldList $fields) {
			// Remove field from parent's beforeExtendingCMSFields
			$fields->removeByName('ChildFieldBeforeExtension', true);

			// Adds own pre-extension field
			$fields->addFieldToTab('Root.Test', new TextField('GrandchildFieldBeforeExtension'));
		});

		$fields = parent::getCMSFields();
		$fields->addFieldToTab('Root.Test', new TextField('GrandchildField'));
		return $fields;
	}
}