Advanced Topics - eXist: A NoSQL Database and Application Development Platform - page 481

If an empty sequence was used for the greeting parameter, we fall back to the
default greeting of hello .
As our third parameter, visitors , is a sequence of one or more values, we obtain
an iterator over the values.
We iterate over each visitor name from visitors and add it to our list of visitors.
We call our business logic, which generates a greeting for each visitor.
This is our isolated business logic, which will generate our greetings.
We create a new ValueSequence to hold each of the greetings that we wish to
return to the XQuery.
We create a new StringValue , which represents an xs:string value to hold each
of our greetings.
We add our greeting to the value sequence.
We return the value sequence, which now contains each of our greetings as
strings. This is then returned to the XQuery by the eval method.
The source code for this example is included in the HelloModule code, as discussed
earlier. To compile and deploy the module, see “Using the Hello World Module” on
page 473 . To test the example, execute the following XQuery from either eXist's Java
Admin Client (see “Java Admin Client” on page 373 ) or eXide (see “eXide” on page
374 ):
xquery version "1.0" ;
declare namespace h = "http://hello" ;
h:say-hello ( "Adam" , (), ( "Elisabeth" , "David" ))
The result of the query should look similar to:
Adam says hello to Elisabeth
Adam says hello to David
You can experiment with providing different values for the second argument to the
function and observe how the results change.
We have now built an XQuery extension function in Java for our internal module
that can both accept multiple parameters of varying cardinality and return a sequence
of results. Every internal module extension function that is written for XQuery in
eXist follows this same pattern.