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 - filter_compound_list 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

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

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 id sub-field if required. It also may leave empty wrapping elements in the output (e.g. the ul in the example below if there are contributors, but none are the required type.

<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>

Method 3 - Custom EPScript function

This is the most complex, but also offers the most flexibility - if you're able to understand the EPrints::Script::Compiled module and write your own functions.

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

 1 ### This should be added to a file e.g. EPRINTS_ROOT/archives/ARCHIVEID/cfg/cfg.d/z_epscript_additions.pl
 2 
 3 # Open block
 4 {
 5 
 6 # Write into EPrints::Script::Compiled
 7 package EPrints::Script::Compiled;
 8 
 9 use strict;
10 
11 # Example usage in citation file:
12 #
13 #  <epc:if test="$item.render_contributors_filtered('http://www.loc.gov/loc.terms/relators/THS',1)">
14 #    <h2><epc:phrase ref="contributor_type_typename_http://www.loc.gov/loc.terms/relators/THS"/></h2>
15 #    <epc:print expr="$item.render_contributors_filtered('http://www.loc.gov/loc.terms/relators/THS')"/>
16 #  </epc:if>
17 #
18 # The first call includes the 'test' parameter, which can be used to determine whether surrounding
19 # elements need to be displayed - in the above example the <h2>.
20  
21 sub run_render_contributors_filtered
22 {
23         my( $self, $state, $eprint, $contributor_type, $test ) = @_;
24 
25         if( !defined $eprint->[0] || ref($eprint->[0]) ne "EPrints::DataObj::EPrint" )
26         {
27                 $self->runtime_error( "Can only call render_contributors_filtered() on eprint objects not ".
28                         ref($eprint->[0]) );
29         }
30 
31         if( !defined $contributor_type )
32         {
33                 $self->runtime_error( "You need to specify a contributor type you want to render." );
34         }
35 
36         my @filtered_contributors = grep{ defined $_->{type} && $_->{type} eq $contributor_type->[0] } @{ $eprint->[0]->value( "contributors" ) };
37 
38         if( $test )
39         {
40                 return [ 0, "BOOLEAN" ] if( scalar @filtered_contributors < 1 );
41                 return [ 1, "BOOLEAN" ];
42         }
43 
44         # NB this is based on EPrints::Extras::render_related_url
45         # It is over-complicated for this use-case, as we could just use
46         # $state->{session}->render_name( $row->{name} )
47         # but if other compound fields are being used with similar code
48         # being able to get to the 'render_value' for the sub fields is useful.
49 
50         my $field = $eprint->[0]->dataset->field( "contributors" );
51         my $f = $field->get_property( "fields_cache" );
52         my $fmap = {};
53         foreach my $field_conf ( @{$f} )
54         {
55                 my $fieldname = $field_conf->{name};
56                 my $field = $field->{dataset}->get_field( $fieldname );
57                 $fmap->{$field_conf->{sub_name}} = $field;
58         }
59 
60         my $ul = $state->{session}->make_element( "ul" );
61 
62         foreach my $row ( @filtered_contributors  )
63         {
64                 my $li = $state->{session}->make_element( "li" );
65                 $li->appendChild( $fmap->{name}->render_single_value( $state->{session}, $row->{name} ) );
66                 if( defined $row->{id} )
67                 {
68                         $li->appendChild( $state->{session}->make_text( " (" ) );
69                         $li->appendChild( $state->{session}->make_text( $row->{id} ) );
70                         $li->appendChild( $state->{session}->make_text( ")" ) );
71                 }
72                 $ul->appendChild( $li );
73         }
74         return [ $ul, "XHTML" ];
75 }
76 
77 } #End block

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