How do you check if a field is empty in drupal 8?

Question

I have a field added to the content type of basic page. It is a select box, which is either checked or unchecked depending on whether or not the page is of the 'getting started' kind. I want to add the class 'getting-started' to the body element in the html if the page is a getting started page, i.e. the box is checked. I want to do this in the .theme file. So essentially I want to check too see if the field is empty, and if it isn't add the class to the body element. Any help would be much appreciated.

Answer 1

To check if a field is empty you can use built-in method isEmpty().

E.g.:

if (!$entity->get('category')->isEmpty()) {
  /** @var EntityInterface $category */
  $category = $entity->get('category')->entity;
  $row['category']['data'] = [
    '#type' => 'link',
    '#title' => $category->get('name')->value,
    '#url' => $category->toUrl(),
  ];
}
else {
  $row['category'] = NULL;
}