View source for Contribute: Plugins/ExportPluginsHelloOld

= Export Plugin Tutorial 1: "Hello, World!" =

In this tutorial you will learn how to create a simple export plugin for EPrints, which will generate a list of titles from the results of a search. A basic knowledge of Perl is needed, but the code will be explained fully.

= Before You Start =

Create a directory for your export plugins in the main export plugin directory (usually /opt/eprints3/perl_lib/EPrints/Plugin/Export). The directory used for these examples is called "MyPlugins"

= HelloExport.pm =

Replace MyPlugins with the name of the directory you have decided to put your export plugins in and place the code below in a file called HelloExport.pm in that directory.

<pre>
package EPrints::Plugin::Export::MyPlugins::HelloExport;

@ISA = ('EPrints::Plugin::Export');

use strict;

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

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

        $self->{name} = 'Hello, World!';
        $self->{accept} = [ 'dataobj/eprint', 'list/eprint' ];
        $self->{visible} = 'all';
        $self->{suffix} = '.txt';
        $self->{mimetype} = 'text/plain; charset=utf-8';

        return $self;
}

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

        return $dataobj->get_value('title')."\n";
}

1;

</pre>


== In More Detail ==
== Housekeeping ==
<pre>
package EPrints::Plugin::Export::Foo::HelloExport;
</pre>
Export plugins need to inherit from the EPrints::Plugin::Export class.
<pre>
@ISA = ('EPrints::Plugin::Export');
</pre>

== Constructor ==
After the implicit class reference, a hash of options is given.
<pre>
        my ($class, %opts) = @_;
</pre>

We create a new export plugin by calling the Eprints::Plugin::Export constructor
<pre>
        my $self = $class->SUPER::new(%opts);
</pre>
Now we set a number of fields to register our new plugin.

This is the name that will appear in the export dropdown menu. The name should therefore be short and descriptive.
<pre>
        $self->{name} = 'Hello, World!';
</pre>

The accept field is a list containing the types of objects this
plugin can deal with. In this case lists of eprints and individual
eprints.
<pre>
        $self->{accept} = [ 'dataobj/eprint', 'list/eprint' ];
</pre>
The visible field denotes the class of user which will be able to see the plugin.
For most export plugins the value 'all' will be required, allowing
all users to see and use the plugin. A value of 'staff' would
make the plugin visible only to repository staff.
<pre>
        $self->{visible} = 'all';
</pre>
The suffix field contains the extension of files exported by the plugin.

The mimetype field defines the [http://en.wikipedia.org/wiki/MIME MIME] type of the files exported by the plugin
You can also specify file encoding, for example 'text/plain; charset=utf-8' to specify plain text, encoded using UTF-8.[http://en.wikipedia.org/wiki/UTF-8 UTF-8] is a Unicode character encoding capable of expressing characters from a large number of character sets and so is usually preferable to [http://en.wikipedia.org/wiki/ASCII ASCII]
<pre>
        $self->{suffix} = '.txt';
        $self->{mimetype} = 'text/plain; charset=utf-8';
</pre>

We then return our plugin reference.
<pre>
        return $self;
</pre>

== Processing DataObjs ==

This method handles the export of each DataObj. DataObjs make up most of the content of an EPrint repository. The three main types are EPrint defining individual eprints, Document defining collections of one or more files belonging to an EPrints, and User which defines users of the repository.

Besides an implicit reference to the Plugin object, this method is also provided with a reference to an individual DataObj. It is called by several [http://en.wikipedia.org/wiki/Common_Gateway_Interface CGI] and command line scripts to export single DataObjs, for instance the item control screen for repository staff. It is also called by the list handling method on each DataObj in a list, for example the results of a search. That will be explained in [[Contribute:_Plugins/ExportPluginList|the next tutorial]].

In the example below we get the title of each DataObj, but there are large number of fields which you can extract from each DataObj. For example try changing "title" to "abstract" to print the abstract of each eprint.

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

        # Return a scalar containing the title.
        return $dataobj->get_value('title')."\n";
}
</pre>

== Finishing Off ==

Standard Perl package requirement.
<pre>
1;

</pre>

= Testing Your Plugin =
Restart your web server and perform a search.

If all is well your plugin should appear in the dropdown menu. Select it and click export. As long as the search provided some results, you should get a list of EPrint titles returned.

== Sample Output ==
[[Image:Exphello.png]]