Editing Contribute: Plugins/ExportPluginsList (section)

= In More Detail =
The above code is very similar to the HelloExport.pm file in [[Contribute:_Plugins/ExportPluginsHello| the previous tutorial]] so only the points where it deviates significantly from that file will be discussed below.

== Housekeeping ==
The package name has been changed to reflect the filename.

<pre>
package EPrints::Plugin::Export::MyPlugins::HelloList;
</pre>

== Constructor ==
Make sure you give each plugin a unique name.

<pre>
        $self->{name} = 'Hello, List!';
</pre>

== Dealing With Lists ==
In this example the output_list method is overridden in the export plugin to provide column headers. The original method just concatenates the output from the output_dataobj subroutine called on every DataObj in the list.

Note that the method is not provided with a bare array of DataObjs, but a List object is provided within the opts hash. To get an array of DataObjs to loop over you must then call that List object's get_record method.

== Filehandles ==
The command line export tool provides the output list method with a filehandle for output in the opts hash, while the [http://en.wikipedia.org/wiki/Common_Gateway_Interface CGI] export uses a value returned from the method. You must deal with the filehandle or you will get no output from the command line tool. In most cases this won't matter, but it is good practice to deal with it.

The best way to handle output is to check if a filehandle has been provided every time something needs to be output. If a filehandle is provided we print to it, otherwise we save the output for later. At the end of the method we either return undef if a filehandle was provided or we return the saved output otherwise.

<pre>
sub output_list
{
        my ($plugin, %opts) = @_;

        my $r = [];

        my $header = "ID\tTitle\n\n";
        if (defined $opts{fh})
        {
                print {$opts{fh}} $header;
        }
        else
        {
                push @{$r}, $header;
        }

        foreach my $dataobj ($opts{list}->get_records)
        {
                my $part = $plugin->output_dataobj($dataobj, %opts);
                if (defined $opts{fh})
                {
                        print {$opts{fh}} $part;
                }
                else
                {
                        push @{$r}, $part;
                }
        }

        if (defined $opts{fh})
        {
                return undef;
        }
        return join('', @{$r});
}
</pre>