Integration - eXist: A NoSQL Database and Application Development Platform - page 331

mented in “REST Server Parameters” on page 531 —but a common use case is to be able
to break the results of your query into smaller pages of results, so we will examine
how to achieve that here.
The REST Server provides a mechanism whereby you can send it an XQuery and
have it cache the results of that query. It will provide you with a session identifier ,
which you can then use in subsequent requests to pull back subsets of those results
(i.e., pages).
For this example, let's imagine that we have added many more documents about peo‐
ple to our /db/people collection, and that this time we wish to find the average age of
people in each settlement . We know that there will be lots of results as our people live
all over the world, so we want to return the results ordered by age ascending ; more
importantly, however, so as not to overwhelm the end user we want to present the
results in pages of 10 results at a time .
Let's consider the XQuery that we might wish to POST to the REST Server API to ach‐
ieve this. Apart from it being a more complex XQuery, note that the cache="yes" ,
start="1" , and max="10" attributes are set on the query element. The cache attribute
instructs the REST Server to return a session identifier for the result set generated by
the query. In addition, start instructs the REST Server to return results from the
cached set starting at position 1 , and max instructs the server to return up to a maxi‐
mum of 10 results from the cached set:
<?xml version="1.0" encoding="UTF-8"?>
<query xmlns= "http://exist.sourceforge.net/NS/exist"
cache= "yes" start= "1" max= "10" >
<text>
<![CDATA[
xquery version "1.0";
for $settlement in distinct-values(/person/residence/location/settlement)
let $average-age := avg(
/person[residence/location/settlement eq $settlement]/born/(year-from-date(
current-date()) - year-from-date(xs:date(./date))))
order by $average-age ascending
return
<settlement>
<name>{$settlement}</name>
<average-age>{$average-age}</average-age>
</settlement>
]]>
</text>
</query>
We send our more complex query to the REST Server API in exactly the same way as
our simpler query, using this cURL command: