Adding multilang fields

How the plugin works

In order to introduce a new field in EPrints (such as the ml_title field), a few things need to take place:

• The field's name and functionality needs to be introduced to the EPrints system via a configuration file located in ~eprints/archives/<reponame>/cfg/cfg.d/.
• EPrints' database needs to be updated to include the new field. This is achieved when user eprints executes (from his home directory):

$ ./bin/epadmin update reponame

• The appropriate phrases need to be added for each field and for each supported language.
• The workflow needs to be edited in order to contain the new fields - and not include the original ones.
• The repository needs to be reloaded, by running:

$ ./bin/epadmin reload reponame

within eprints user's home directory.

The following sections explain each step in detail, where we are using ml_title as our example field. The code snippets are just for demonstration purposes (and proof of concept). If you want to see the final, working implementation, you should look at the source code of the plugin.

Introducing ml_title field in EPrints

We create the file: ~eprints/archives/<reponame>/cfg/cfg.d/zz_multilang_field.pl with the following content:

#define local fields
my $local_fields = [
{
    name => 'ml_title',
    type => 'multilang',
    multiple => 1,
    fields => [ { sub_name => "text", type => "longtext", input_rows => 3, make_single_value_orderkey => 'EPrints::Extras::english_title_orderkey' } ],
    input_add_boxes => 1,
},

{
    name => 'title',
    type => 'virtualwithvalue',
    virtual => 1,

    get_value => sub
    {
        my ($eprint) = @_;
        if ($eprint->is_set('ml_title'))
        {
            my $lang = $eprint->repository->get_langid;
            my $lang_set = 0;
            my $vals = $eprint->get_value('ml_title');
            my $title = '';
            if (!$lang)
            {
                $lang_set = 1;
            }
            else
            {
                # set the default lang's text as title
                foreach my $v1 (@{$vals})
                {
                    if ($v1->{lang} eq $lang)
                    {
                        $title = $v1->{text};
                    }
                }
            }
            # if the language is not set or I can't find an abstract in the 
            # user's language, get the first object's text as abstract
            if ($lang_set or $title eq '')
            {
                $title = $vals->[0]->{text};
            }
            return $title;

        }
        return undef;
    },

    set_value => sub
    {
        my ($eprint, $value) = @_;
        my $lang = 'en';
        #only use this on imports, NOT if the value is already set
        if ($eprint->is_set('ml_title'))
        {
            return;
        }
        if ($value)
        {
            $eprint->set_value('ml_title', [{lang=>$lang, text=>$value}]);
        }
    }
},
];

#create lookup hash of local field names
my $local_fieldnames = {};

foreach my $f (@{$local_fields})
{
    $local_fieldnames->{$f->{name}} = 1;
}

#merge in existing field configurations
foreach my $f (@{$c->{fields}->{eprint}})
{
    if (!$local_fieldnames->{$f->{name}})
    {
     push @{$local_fields}, $f;
    }
}

#overwrite original array of configured fields
$c->{fields}->{eprint} = $local_fields;

Where we can see that our new ml_title field is of type virtualwithvalue (which we'll explain later in this section) and implements two functions: get_value and set_value. Both these functions are used by EPrints API and their existence, as well as their return values, are critical for EPrints to work properly, and do exactly what their names suggest. In the end of our example code one can see how a custom field can be added in the list of EPrints fields.