I have added a custom button to a form:
$form['actions']['autotag_content'] = [
'#type' => 'button',
'#value' => 'Autotag Content',
'#ajax' => [
'callback' => ['\Drupal\taxonomy_migrate\taggerService', 'tagContent'],
'wrapper' => ['block-adminimal-theme-content'],
'progress' => [
'type' => 'throbber',
'message' => 'Tagging content',
],
],
];
Then in the callback I want to add or remove entities from an entity reference field on the form. This would then get sent back to the browser and rerendered. I don't want the changes to be save, I just want them populated in the form and then the user can accept the changes.
For the sake of this example, I have simplified this to just demonstrate the point. I would like to add two entity references to field_tax_subjects and have the frontend form rerender. Currently, the frontend form rerenders, but doesn't reflect the changes
public static function tagContent(array &$form, FormStateInterface &$form_state) {
$node = $form_state->getFormObject()->getEntity();
$node->field_tax_subjects[] = 12345;
$node->field_tax_subjects[] = 23456;
$form = \Drupal::service('entity.form_builder')->getForm($node);
$form_state->setRebuild();
return $form;
}