Unchecking a boolean field on form render

Question

I have a content type that has a boolean field (checkbox) that editors need to always re-check on saving a new revision, if they want the value to still be true. Otherwise, it would be saved as false.

I'm using a hook_form_node_form_alter to modify the $form before the page is shown to the Editor.

public function my_module_form_node_form_alter(&$form, &$form_state, &$form_id) 
{
   $form['field_my_boolean_field']['#value'] = 0;
}

I've tried something similar to the above and have also tried #checked and #default_value in place of #value but nothing seems to work. The checkbox always renders checked (as it is saved in the database). How can I uncheck this boolean field when the form is rendered? Note that I do not want to change the actual value of the field for this node, just make it unchecked in the UI when the form for this content is shown.

Answer 1

You can use hook_ENTITY_TYPE_prepare_form() to change entity values before the entity form is built:

/**
 * Implements hook_ENTITY_TYPE_prepare_form() for Nodes.
 */
function mymodule_node_prepare_form(\Drupal\node\NodeInterface $node, $operation, \Drupal\Core\Form\FormStateInterface $form_state) {
  if ($node->getType() != 'my_content_type') {
    return;
  }
  if ($operation == 'edit') {
    $node->field_my_boolean_field->value = 0;
  }
}

This changes the value of the field for this node, but only temporary as long as the user doesn't submit the form.