Insert task to Queue only if unique

Question

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.

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))
    ->fields(array(
        '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:

DrupalQueue::get('update_profile_tasks')->createQueue();

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.