Drupal 8 - Custom validation on entity creation

Drupal 8 - Custom validation on entity creation

//prevent 2 or more of the CTA paragraphs from being chosen in a paragraph reference field

function mymodule_form_node_form_alter(&$form, FormStateInterface $form_state) {
  $node = $form_state->getFormObject()->getEntity();
  // Add validation to nodes by type
  if(in_array($node->getType(),['campaign_page','case_study','event','insight','resource'])) {
     $form['#validate'][] = '_mymodule_node_form_validate';
  }
}

function _mymodule_node_form_validate(&$form, FormStateInterface $form_state) {
  // Validates that we don't have two CTAs chosen in paragraph reference
  $under_content_paragraphs = $form_state->getValue('field_under_content_sections');
  if (!empty($form_state->getValue('field_under_content_sections'))) {
    if(count($under_content_paragraphs) == 2) {
      $keys_of_paragraphs = array_keys($under_content_paragraphs);
      $has_one_cta_form = isset($under_content_paragraphs[$keys_of_paragraphs[0]]['subform']['field_cta'])
                          || isset($under_content_paragraphs[$keys_of_paragraphs[0]]['subform']['field_half_width_ctas']);
      $has_other_cta_form = isset($under_content_paragraphs[$keys_of_paragraphs[1]]['subform']['field_cta'])
                            || isset($under_content_paragraphs[$keys_of_paragraphs[1]]['subform']['field_half_width_ctas']);
      if($has_one_cta_form && $has_other_cta_form) {
          $form_state->setError($form['field_under_content_sections'], 'Cannot have two CTA paragraphs selected in the Under Content Section.');
      }
    }
  }
}