Prevent node from being saved

Question

So, this seems like a rather simple task but I've been stuck on it for a while.

I need either in hook_node_presave or in hook_node_submit (but NOT in hook_node_validate) to check for a field value in a node and according to that value choose whether or not to cancel the node saving procedure.

How do I do that? (The canceling part, not the checking part ;) )

Answer 1

Implement drupal_goto()

I believe this function obliterates any followup processing other than saving session data and forwards the user immediately on to a new page.

Excerpt from Drupal.org: drupal_goto();

This function ends the request; use it instead of a return in your menu callback.

To define where the users will be sent to, simply pass the same data you would to the url() function.

For example:

drupal_goto('node/44');  // Sends users to yoursite.com/node/44

An update regarding the drupal_goto() function from a submit handler (See https://drupal.stackexchange.com/a/33281):

//Note from https://drupal.stackexchange.com/a/33281
//When using drupal_goto() from a submit function you may need to be more aggressive. 
$url = url("node/$nid");
header("Location:$url");
drupal_set_message(t('Message to be displayed in the next page'));
drupal_exit(); 

Answer 2

I've found that the best way is to just thrown an error during presave. Here's a simple example:

function mymodule_node_presave($node){
  if(empty($node->title)){
    throw new Exception('Error saving node: Title cannot be empty');
  }
}

The node_save() function has a try...catch block wrapping the presave step that will catch the exception.

The advantage of this over drupal_goto() is that, if you're importing multiple nodes, it will skip the current node and proceeed to the next one. This is great if you're using something like the Feeds module. In contrast drupal_goto() will exit immediately and may interfere with other steps in the request or cron, which will break importing multiple nodes.