I wanted a way to only insert items into the Queue when it was not already added. I want to have a large queue and work my way through it, simply adding as required. Previously I was deleting the queue and recreating on a set time table.

I couldn't find any way of doing this, or any discussion other than 'it's not possible.

I created the method below. I have not used it for huge queues yet, but I post it here in the hope that better options if available might get posted too.

1 Answer 1


Create a class to extend the systemqueue. I called mine Unique. This will serialise the data use db_merge to insert only if it doesn't exist.

class Unique extends SystemQueue {

  public function createItem($data) {

    // save doing this twice
    $serial_data = serialize($data);

    // ignoring expire
    $query = db_merge('queue')
    ->key(array('name' => $this->name, 'data' => $serial_data))
        'name' => $this->name,
        'data' => $serial_data,
        'created' => time(),
    return (bool) $query->execute();

You then add the variables to hook_install() or hook_enable().

variable_set('queue_class_[your queue name]', 'Unique');

matching [your queue name] to the queue name, e.g if you used this:


the variable would be:

variable_set('queue_class_update_profile_tasks', 'Unique');

Thanks to this for getting me on track. Updated answer to be cleaner thanks to comment suggestions.

  • You could simply use db_update() instead of checking if there is a row for that data. db_update() updates the existing row, or creates it when it doesn't exist.
    – apaderno
    Jun 22, 2015 at 9:58
  • Also, you don't use variable_set() in this case, but $conf in settings.php since it is something that should be changed before Drupal completes its bootstrap phase.
    – apaderno
    Jun 22, 2015 at 10:00
  • @kiam Think you mean db_merge()?
    – Clive
    Jun 22, 2015 at 10:07
  • Wouldn't I need to get the key if I use db_merge, and doesn't that basically check if it exists, and then updates/inserts? I am not sure that makes it better? Regarding the variable, I'd assumed this would be done on module install. I'll make that clearer.
    – Paul
    Jun 22, 2015 at 10:12
  • @Clive Ops... Yes, that.
    – apaderno
    Jun 22, 2015 at 10:17

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