Updating the postDate field from a plugin?

Question

I think I'm almost there with this one but obviously missing something as the postDate is not updating. I have the following in an onSaveEntry event. It's saying it's successful but the postDate does not change. Ideally I want this to update whether the entry is enabled or not.

public function onSaveEntry(Event $event)
{
    $entry = $event->params['entry'];
    // set postDate from assignedDate
    if($user->admin) {
        if($entry->assignedDate && $entry->assignedTimeslot) {
            $timeslot = $entry->assignedDate.' '.$entry->assignedTimeslot.'.000000';
            $params = $entry->postDate = $timeslot;
            $success = craft()->elements->saveElement($entry, $params);
        }
    }
    return $event;
}

Answer 1

$timeslot isn't formatted correctly to be used as the postDate. I'd create a field that takes a date and a time and then use DateTimeHelper::formatTimeForDb() to format for use as postDate.

You can't modify the postDate until after the entry has been saved - so will need to resave the entry with the newly set postDate. More info as to why you have to do this here.

craft()->on( 'entries.onSaveEntry', function( Event $event ){

  // Grab the entry from post request
  $entry = $event->params['entry'];

  // Get logged in user
  $user = craft()->userSession->getUser();

  if ( $user && $user->admin ) {
    $timeSlot = $entry->getContent()->assignedTimeslot;

    // If the postDate and Timeslot don't match (stops infinite loop)
    if ( !( $entry->postDate == $timeSlot ) ) {

        // Set postDate to timeSlot date
        $entry->postDate = DateTimeHelper::formatTimeForDb( $timeSlot );

        // Resave entry
        craft()->entries->saveEntry( $entry );
    }
  }
});

Answer 2

Thanks to @LukePearce I managed to re-write the code to work as follows:

craft()->on( 'entries.onSaveEntry', function( Event $event ){

  // Grab the entry from post request
  $entry = $event->params['entry'];

  // Get logged in user
  $user = craft()->userSession->getUser();

  // Set the timeslot
  $timeSlot = $entry->getContent()->assignedDate.' '.$entry->getContent()->assignedTimeslot;

  // Create a new dateTime object from timeslot
  $postDate = new \DateTime($timeSlot);

  // Check the postDate has changed
  if ($entry->postDate != $postDate) {

    // check user is set and is admin
    if ($user && $user->admin) {

      // Set entry postDate to new postDate
      $entry->postDate = $postDate;

      // Resave entry
      $success = craft()->entries->saveEntry($entry);

    }
   }
});

Answer 3

I have written a plugin for this exact use case. You can configure what time is set as the postDate or expiryDate via a Twig template.

https://github.com/carlcs/craft-autoexpire