如何在drupal节点表单中检测其编辑或添加表单？

function mymodule_form_node_form_alter(&$form, &$form_state) {
  $node = $form_state[\'node\'];

  if (!isset($node->nid) || isset($node->is_new)) {
    // This is a new node.
  }
  else {
    // This is not a new node.
  }
}

if ($node->is_new) {do_something_for_new_node();}