difference between create new and edit node in form alter

Question

I have a alter section about particular content type.i need to 2 method in alter form. first in create new and second for edit node. in form alter how i can find out this create new from or edit from

with dsm($form) in from_alter i get result with serveral difference between those,what is the popular and the best way to distinguish those from each other? is this a good way?

    if(isset($form['nid']['#value']))
     'means in edit form'
    else 
     'means in create new from'

Answer 1

Yes, you have to check if the node ID exists or not.

Answer 2

If you look at the code of node_object_prepare(), which is called from node_form() (the form builder for the node edit/create form), it contains the following code.

  // If this is a new node, fill in the default values.
  if (!isset($node->nid) || isset($node->is_new)) {
    foreach (array('status', 'promote', 'sticky') as $key) {
      // Multistep node forms might have filled in something already.
      if (!isset($node->$key)) {
        $node->$key = (int) in_array($key, $node_options);
      }
    }
    global $user;
    $node->uid = $user->uid;
    $node->created = REQUEST_TIME;
  }

In an implementation of hook_form_BASE_FORM_ID_alter(), it is enough to use code similar to the following one.

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 the node is new, then the form is creating a node; if the node is not new, then the form is editing an existing node.