Isolate BlockLink field

TestObject.php

<?php

use DNADesign\Elemental\Extensions\ElementalPageExtension;
use DNADesign\Elemental\Models\BaseElement;
use SilverStripe\Admin\ModelAdmin;
use SilverStripe\Control\Director;
use SilverStripe\ORM\DataObject;

class TestObject extends DataObject
{

    private static $table_name = 'TestObject';
    private static $extensions = [ElementalPageExtension::class];

    public function CMSEditLink() {
        $link = 'admin/test-model-admin/TestObject/EditForm/field/TestObject/item' . $this->ID;
        return Director::absoluteURL($link);
    }

    public function Link($action = null)
    {
        return '';
    }

}

class TestObjectModelAdmin extends ModelAdmin
{
    private static $managed_models = [TestObject::class];
    private static $url_segment = 'test-model-admin';
}

class CallToActionBlock extends BaseElement
{
    private static $db = [
        'CallToActionLink' => 'Link',
    ];

    private static $table_name = 'CallToActionBlock';

    public function getType()
    {
        return 'Call to action block';
    }

    /**
     * For the frontend, return a parsed set of data for use in templates
     *
     * @return ArrayData|null
     */
    public function CallToActionLink()
    {
        return $this->decodeLinkData($this->getField('CallToActionLink'));
    }

    /**
     * Given a set of JSON data, decode it, attach the relevant Page object and return as ArrayData
     *
     * @param string $linkJson
     * @return ArrayData|null
     */
    protected function decodeLinkData($linkJson)
    {
        if (!$linkJson || $linkJson === 'null') {
            return;
        }

        $data = ArrayData::create(json_decode($linkJson));

        // Link page, if selected
        if ($data->PageID) {
            $data->setField('Page', self::get_by_id(SiteTree::class, $data->PageID));
        }

        return $data;
    }
}