Editing How to display specific contributors

Based on this question, asked on the EPrints Tech list:
''How can I add the field “Thesis Advisor” from Contributors to the Abstract Pages?''

'''Note:''' The question on the tech list specified EPrints 3.4.2. The below is based on 3.3.16, but may be useful as a starting point.

Below are three approaches that may do what you need.

== Method 1 - EPScript function ==
1) In EPScript, there is an undocumented function - <code>filter_compound_list</code> which accepts:
* a field (''contributors'')
* a sub-field name to filter on (''type'')
* a value to filter to (''http://www.loc.gov/loc.terms/relators/THS'') 
* the field to return (''name'')

This can produce a text-string of one field from the compound field. If a thesis had two supervisors, the following example would produce:

''Smith, John and Bond, James''

<source lang="xml">
  <epc:if test="contributors">
    <epc:print expr="filter_compound_list(contributors,'type','http://www.loc.gov/loc.terms/relators/THS','name')" />
  </epc:if>
</source>

== Method 2 - EPScript logic - ''foreach'' ==

This method is a bit more flexible, but you have to construct the values from the parts manually. It does allow you to reference the <code>id</code> sub-field if required.
It also may leave empty wrapping elements in the output (e.g. the <code>ul</code> in the example below if there are contributors, but none are the required type.

<source lang="xml">
<epc:if test="contributors">
  <ul>
    <epc:foreach expr="contributors" iterator="contr">
      <epc:if test="$contr{type}='http://www.loc.gov/loc.terms/relators/THS'">
        <li>
          <epc:print expr="$contr{name}{given}" /> <epc:print expr="$contr{name}{family}" />
          <epc:if test="$contr{id}">(<epc:print expr="$contr{id}"/>)</epc:if>
        </li>
      </epc:if>
    </epc:foreach>
  </ul>
</epc:if>
</source>

== Method 3 - Custom EPScript function ==
This is the most complex, but also offers the most flexibility - if you're able to understand the <code>EPrints::Script::Compiled</code> module and write your own functions.

There are two parts - adding custom methods to EPScript, and calling them from the citation file.

<syntaxhighlight lang="perl" line>
### This should be added to a file e.g. EPRINTS_ROOT/archives/ARCHIVEID/cfg/cfg.d/z_epscript_additions.pl

# Open block
{

# Write into EPrints::Script::Compiled
package EPrints::Script::Compiled;

use strict;

# Example usage in citation file:
#
#  <epc:if test="$item.render_contributors_filtered('http://www.loc.gov/loc.terms/relators/THS',1)">
#    <h2><epc:phrase ref="contributor_type_typename_http://www.loc.gov/loc.terms/relators/THS"/></h2>
#    <epc:print expr="$item.render_contributors_filtered('http://www.loc.gov/loc.terms/relators/THS')"/>
#  </epc:if>
#
# The first call includes the 'test' parameter, which can be used to determine whether surrounding
# elements need to be displayed - in the above example the <h2>.
 
sub run_render_contributors_filtered
{
        my( $self, $state, $eprint, $contributor_type, $test ) = @_;

        if( !defined $eprint->[0] || ref($eprint->[0]) ne "EPrints::DataObj::EPrint" )
        {
                $self->runtime_error( "Can only call render_contributors_filtered() on eprint objects not ".
                        ref($eprint->[0]) );
        }

        if( !defined $contributor_type )
        {
                $self->runtime_error( "You need to specify a contributor type you want to render." );
        }

        my @filtered_contributors = grep{ defined $_->{type} && $_->{type} eq $contributor_type->[0] } @{ $eprint->[0]->value( "contributors" ) };

        if( $test )
        {
                return [ 0, "BOOLEAN" ] if( scalar @filtered_contributors < 1 );
                return [ 1, "BOOLEAN" ];
        }

        # NB this is based on EPrints::Extras::render_related_url
        # It is over-complicated for this use-case, as we could just use
        # $state->{session}->render_name( $row->{name} )
        # but if other compound fields are being used with similar code
        # being able to get to the 'render_value' for the sub fields is useful.

        my $field = $eprint->[0]->dataset->field( "contributors" );
        my $f = $field->get_property( "fields_cache" );
        my $fmap = {};
        foreach my $field_conf ( @{$f} )
        {
                my $fieldname = $field_conf->{name};
                my $field = $field->{dataset}->get_field( $fieldname );
                $fmap->{$field_conf->{sub_name}} = $field;
        }

        my $ul = $state->{session}->make_element( "ul" );

        foreach my $row ( @filtered_contributors  )
        {
                my $li = $state->{session}->make_element( "li" );
                $li->appendChild( $fmap->{name}->render_single_value( $state->{session}, $row->{name} ) );
                if( defined $row->{id} )
                {
                        $li->appendChild( $state->{session}->make_text( " (" ) );
                        $li->appendChild( $state->{session}->make_text( $row->{id} ) );
                        $li->appendChild( $state->{session}->make_text( ")" ) );
                }
                $ul->appendChild( $li );
        }
        return [ $ul, "XHTML" ];
}

} #End block
</syntaxhighlight>

The above example is also available at: https://gist.github.com/jesusbagpuss/2efc96ed05cf9121b925063a20677120

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