Editing EPrints Glossary (section)

=== Virtual metadata field ===
This is a [[#Metadata field|metadata field]] whose values are not actually stored in the database but are generated dynamically by a function probably using the values of one or more other metadata fields.  This may be useful when editing the [[#Citation|citation]] style as part of designing your [[#Archive|archive]]'s [[#Abstract page|abstract page]], as being able to reference a field is very straightforward.  A basic example might be that you want to display on the abstract page the number of [[#Document|documents]] for the [[#EPrint|eprint]].  Creating a virtual field for the eprint called ''num_docs'' might look as follows:
 {
   name => 'num_docs',
   type => 'int',
   virtual => 1,
   render_value => 'get_num_docs',
 },
Then you would define a function in a configuration file and assign it to <tt>$c->{get_num_docs}</tt>.  You could then simply include this in the ''summary_page.xml'' eprint citation file as:
 <epc:print expr="num_docs"/>