[EP-tech] Changes to EPrints

[cjg at ecs.soton.ac.uk (Christopher Gutteridge)]

I left this list a long time ago, but I see the issue of the open source 
status has been raised, as was inevitable.


EPrints is still listed as a GNU package 
<https://directory.fsf.org/wiki/EPrints>. Getting my software officially 
on the FSF list was an achievement I remain deeply proud of. Unusually, 
the Free Software Foundation agreed to allow the copyright to remain 
with University of Southampton as they could be trusted to defend the 
free & open nature of the software. Any changes to the free and open 
nature of EPrints, the software I put years of my life into, have been 
made without any discussion with, or blessing from, me.





In other news, I've been working on our local EPrints repository for the 
first time in many years and have come up with  a couple of features, 
and a fix, that may be useful to others.


1.
Debugging EPC files. Add this to a config.d/ file,

use Data::Dumper;
sub EPrints::Script::Compiled::run_dumper
{
         my( $self, $state, $data ) = @_;

         my $pre = $state->{session}->make_element( "pre" );
         $pre->appendChild( $state->{session}->make_text( "TYPE: 
".$data->[1]."\nVALUE: ".Dumper( $data->[0] ) ) );
         return [ $pre , "XHTML" ];
};

and then you can use

<epc:print expr="dumper(creators)" /> to look at the type and structure 
of a variable in an EPC file. It's a bit hokey, but handy when doing 
more complex staff.


2.
EPScript again; Subproperty() method. This code adds a method to the 
EPScript which lets you get at a single value from a compound field. Use 
in conjunction with <epc:foreach> over a multiple compound field. The 
type of the resulting value is of the subtype so the default rendering 
will be used making life much easier. In retrospect this is an obvious 
and missing feature that should have been added when I created EPScript 
in the first palce.

eg. Soton has a compound multiple dates field.

     <epc:foreach expr="$item{dates}" iterator="date">
       <div class='uos-eprints-dv'><span 
class='uos-eprints-dv-label'><epc:print 
expr="$date.subproperty('date_type')" /> date:</span> <epc:print 
expr="$date.subproperty('date')" /></div>
     </epc:foreach>

Code:
sub EPrints::Script::Compiled::run_subproperty
{
         my( $self, $state, $objvar, $value ) = @_;

         if( !defined $objvar->[0] )
         {
                 $self->runtime_error( "can't get a property 
{".$value->[0]."} from undefined value" );
         }
         my $ref = ref($objvar->[1]);

         if( $ref !~ m/::/ || ! $objvar->[1]->isa( 
"EPrints::MetaField::Compound" ) )
         {
                 $self->runtime_error( "can't get a subproperty from 
anything except a compound field value, when trying to get 
".$value->[0]." from a $ref" );
         }
         my $field = $objvar->[1];
         if( $field->get_property( "multiple" ) )
         {
                 $self->runtime_error( "can't get a subproperty from a 
multiple field." );
         }

         my $fc = $field->get_property( "fields_cache" );
         my $sub_field;
         my @ok = ();
         foreach my $a_sub_field ( @{$fc} )
         {
                 push @ok, $a_sub_field->{sub_name};
                 if( $a_sub_field->{sub_name} eq $value->[0] )
                 {
                         $sub_field = $a_sub_field;
                 }
         }
         if( !defined $sub_field ) {
                 $self->runtime_error( "unknown sub-field of a compound: 
".$value->[0].". OK values: ".join( ", ", @ok )."." );
         }
         $sub_field->set_property( "multiple", 0 );

         return [
                 $objvar->[0]->{ $value->[0] },
                 $sub_field ];
};


3.
Subroutine redefined warning messages. These appear to be part and 
parcel of some EPrints plugins and are annoying. Code shouldn't ship 
with "just ignore the warnings".
If you are intentionally overriding a method in Perl you can remove the 
existing one first to get rid of a needless warning.
eg. if you need to override
sub EPrints::Badgers::render  {
  #stuff
}
you can place this before hand:
BEGIN { delete $EPrints::Badgers::{render}; }
to remove the default subroutine, then you'll not get those annoying 
warnings.


-- 
Christopher Gutteridge -- http://users.ecs.soton.ac.uk/cjg

University of Southampton Open Data Service: http://data.southampton.ac.uk/
You should read our Web & Data Innovation blog: http://blogs.ecs.soton.ac.uk/webteam/