Editing Dataset Manipulation, Triggers and Events (section)

=Triggers= 

Triggers in EPrints and like message queues, you register a function which is called when a trigger point is hit.

There are lots of triggers in EPrints which are defined in the EPrints/Const.pm file however not all of them have trigger points at the time of writing. 

Ideally we would want to use the EP_TRIGGER_FILES_MODIFIED as our trigger, however this is one of the ones which currently has no trigger point. So instead we are going to register our code against the EP_TRIGGER_AFTER_COMMIT on the '''file''' dataset only.

There are two types of trigger:

* Repository Triggers: General purpose triggers which should always be called with the same params and types. 
* Dataset Triggers: Similar to repository triggers except they operate on a single dataset which changes depending on the trigger point.

We are thus going to register our trigger against the '''file''' dataset using a dataset trigger. 

==Our Dataset Trigger==

Triggers are registered in the repository config on load, thus the code can sit in our config file under cfg/cfg.d/. 

Don't forget to reload the config to load the trigger. 

  $c->add_dataset_trigger( "file", EP_TRIGGER_AFTER_COMMIT , sub {
        my ( %params ) = @_;
  
        my $repository = $params{repository};
  
        return undef if (!defined $repository);
  
        if (defined $params{dataobj}) {
                my $file = $params{dataobj};
                my $file_id = $file->value("fileid");
  
                $repository->dataset( "event_queue" )->create_dataobj({
                        pluginid => "Event::ScanFile",
                        action => "scanfile",
                        params => [$file_id],
                });
        }
  
 });