Create Export Plugins

Export plugins for anything but eprints are beyond the scope of this howto.

Imagine we want to create an export plugin that will take a group of eprints (or a single eprint) and output a csv file containing a list of who deposited the eprints, and the dates on which they were deposited.

Essentials

The top of the plugin should look like this:

package EPrints::Plugin::Export::DepositorActivity;

use Unicode::String qw( utf8 );
use EPrints::Plugin::Export;
use EPrints::DataObj::User;
@ISA = ( "EPrints::Plugin::Export" );
use strict;

sub new
{
       my( $class, %params ) = @_;

       my $self = $class->SUPER::new( %params );

       $self->{name} = "Depositor Activity";
       $self->{accept} = [ 'list/eprint', 'dataobj/eprint' ];
       $self->{visible} = "all";
       $self->{suffix} = ".csv";
       $self->{mimetype} = "text/csv";

       return $self;
}

This will create a filter object, and set a number of configuration constants:

• name - The name of the filter
• accept - A list detailing what the filter will take as inputs. In this case, a list of eprints or a single eprint. It is possible to write filters for dataobj types 'eprint', 'user', 'subject', 'history', 'access' and '*' (all).
• visible - Who can see this filter. It's set to 'all' above so that anyone can use it. It could be set to 'staff' to only allow repository staff to use it. If set to 'API' then the filter is not available through the web interface.
• suffix - Appended to the url to create a filename extension.
• mimetype - Should be set to the correct mime type for the output of the filter.

Note that 'name' and 'accept' are essential. These allow the filter to register itself with EPrints.

We will be extracting the username of the depositor, so we need to use 'EPrints::DataObj::User'.

Converting the dataobj

The 'output_dataobj' function takes a dataobj (in our case an eprint object) and returns a perl scalar which will be the output. We are going to extract some data from the dataobj using EPrints API calls.

Note that by convention, '$plugin' is used instead of '$self'.

sub output_dataobj
{
      my( $plugin, $dataobj ) = @_;

      my $r = "";
      if ($dataobj->exists_and_set("userid"))                                       #userid may not be set if the deposit was done by a script.
      {
              my $session = $plugin->{"session"}; 
              my $userid = $dataobj->get_value( "userid" );
              my $depositor_obj = new EPrints::DataObj::User($session, $userid);    #create a user object
              my $depositor = $depositor_obj->get_value( "username" );              #get the user ID
              if ($depositor =~ m/[\n" ,]/)                                         #Check for illegal CSV characters
              {
                      $depositor =~ s/"/""/g;                                       #escape quotes
                      $depositor = '"' . $depositor . '"';                          #delimit text
              }
              $r .= $depositor;
      }
      else
      {
              $r .= '"Depositor Unknown"';
      }
      $r .= ',' . $dataobj->get_value( "datestamp" ) . "\n";                        #datestamp is always set, and contains a space so needs delimiting

      return $r;
}

Notes:

• Retreiving the username takes a little fancy footwork because the EPrints object contains depositor userids. We need to create a user object and get the username from that.
• We use '$dataobj->get_value' to retrieve metadata from the eprint (or user) objects.
• As we're outputting in CSV, we need to do a little normalisation.

Put it in a Module

Put all this into a file called 'DepositorActivity.pm' and save the file into the 'eprints3/perl_lib/EPrints/Plugin/Export/' directory. Don't forget to add this to the bottom of the file:

1;

Adding Column Headings

The 'output_dataobj' runs on a single EPrint. If the plugin runs over a list of eprints (we've given it that capability), the default behaviour is to run 'output_dataobj' on every eprint in the list and concatenate the results.

The output_list function is what handles the lists. This takes itself ($plugin) and a hash (%opts) as arguments. The %opt hash contains the list. It could also contain a filehandle. When writing 'output_list', you need to check for the filehandle and if present, print to it. If it's not present, return the results as a scalar.

Here is an output_list function that will add column headings to our CSV file.

sub output_list
{
       my( $plugin, %opts ) = @_;
       my $r = [];                                                      #array for results accumulation
       my $part;

       $part = '"User ID","Date Stamp"' . "\n";                         #column headings
       if( defined $opts{fh} )                                          #write to file or accumulate headings
       {
               print {$opts{fh}} $part;
       }
       else
       {
               push @{$r}, $part;
       }

       foreach my $dataobj ( $opts{list}->get_records )                 #Iterate over list
       {
               $part = $plugin->output_dataobj( $dataobj, %opts );      #call output_dataobj
               if( defined $opts{fh} )                                  #write to file or accumulate results
               {
                        print {$opts{fh}} $part;
               }
               else
               {
                       push @{$r}, $part;
               }
       }

       if( defined $opts{fh} )                                          #Don't return results if writing to file.
       {
               return;
       }
       return join( , @{$r} );
}

The conditionals for printing to a file make the function look overly complex. Here it is if you ignore file handles (which you certainly shouldn't do):

sub output_list
{
       my( $plugin, %opts ) = @_;
       my $r = [];                                                      #array for results accumulation
       my $part;

       $part = '"User ID","Date Stamp"' . "\n";                         #column headings
       push @{$r}, $part;
       foreach my $dataobj ( $opts{list}->get_records )                 #Iterate over list
       {
               $part = $plugin->output_dataobj( $dataobj, %opts );      #call output_dataobj
               push @{$r}, $part;
       }
       return join( , @{$r} );
}