XQuery Extension Modules - eXist: A NoSQL Database and Application Development Platform - page 510

metadata
Description
Document key/value metadata functions
Namespace
md="http://exist-db.org/metadata"
Type/default status
Java; enabled in $EXIST_HOME/conf.xml ; enabled in $EXIST_HOME/extensions/
build.properties
Class
org.exist.storage.md.xquery.MetadataModule
This module incudes functions for associating key/value metadata pairs with a docu‐
ment, rerieving key/value pairs associated with documents, and searching for docu‐
ments based on key/value pairs.
While useful, the metadata module should be considered highly
experimental and not yet ready for production use.
For example, say you wish to store a key/value pair of metadata for the docu‐
ment /db/my-docs/doc1.xml . You can do this as follows:
xquery version "1.0" ;
import module namespace md = "http://exist-db.org/metadata" ;
md:set-value ( doc ( "/db/my-docs/doc1.xml" ), "roll-number" , 12345 )
Each time you set a metadata key/value pair, you are also returned a UUID (univer‐
sally unique identifier) that represents the intersection of document , key , and value .
You can find all of the metadata keys set for a document like so:
xquery version "1.0" ;
import module namespace md = "http://exist-db.org/metadata" ;
md:keys ( doc ( "/db/my-docs/doc1.xml" ))
And you can retrieve the document(s) with the metadata key roll-number and the
value 12345 like this: