Dataset Manipulation, Triggers and Events

In this exercise, we are going to look at a lot of capabilities of EPrints combined in one exercise.

The overall aim is to add a Trigger which queues an Event on the indexer to scan a file for it's mime type (according to the unix file command) and update this data in the file dataset

We shall also add a new dataset although we won't specifically be using it.

Adding To Datasets

This is done with a config file under cfg/cfg.d/ which we can call package_name.pl for example.

The following shows an example of adding the file_cmd_mime to the file dataset.

 $c->add_dataset_field( "file", {
       name => "file_cmd_mime",
       type => "text",
 }, reuse => 1 );

Note that we can specify the reuse flag to say if we can reuse this field if it already exists. If this is set to 0 (or not defined) and the field already exists the package install will fail.

Note also that if none of the config files define the field, then it is assumed it no longer required and it is removed (data included). Some investigation is need to see if upgrades work... (:S)

Adding New Datasets

Adding new datasets is much the same as adding to an existing one other than the fact we need to define the dataset and the basic class wrappers.

 # Define the dataset
 $c->{datasets}->{package_dataset} = {
      class => "EPrints::DataObj::PackageDataset",
      sqlname => "package_dataset",
      datestamp => "datestamp",       
      sql_counter => "datasetid",
 };
 
 # Add fields to the dataset
 $c->add_dataset_field( "package_dataset", { name=>"datasetid", type=>"counter", required=>1, can_clone=>0, sql_counter=>"datasetid" }, );
 $c->add_dataset_field( "package_dataset", { name=>"name", type=>"text", required=>0, }, );
 $c->add_dataset_field( "package_dataset", { name=>"count", type=>"int", required=>0, }, );
 
 # Define the class, this can either be done using a new file in the right place, or by using this override trick, open a '{' and then continue as it this is new file
 {
   package EPrints::DataObj::PackageDataset;
 
   our @ISA = qw( EPrints::DataObj );
   
   # The new method can simply return the constructor of the super class (Dataset)
   sub new
   {
       return shift->SUPER::new( @_ );
   }
 
   # This method is required to just return the dataset_id.
   sub get_dataset_id
   {
       my ($self) = @_;
       return "package_dataset";
   }
 
 }