Editing Create Export Plugins (section)

===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.
<pre>
 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} );
 }
</pre>
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):
<pre>
 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} );
 }
</pre>