Pre-order and cache sequences for sorting

This module allows you to create a pre-sorted sequence in memory to speed up sorting via "order by" in XQuery. Create an ordered sequence using memsort:create by mapping each element to a sort key (an arbitrary atomic value). Calling memsort:get for the same element at any later point will return an integer corresponding to the ordinal position of that element in the sorted sequence (or empty if no mapping is found).

Example for creating a sorted sequence:

declare namespace tei="http://www.tei-c.org/ns/1.0";

import module namespace memsort="http://exist-db.org/xquery/memsort" at "java:org.existdb.memsort.SortModule";

memsort:create(
    "record-date", 
    collection("/db/apps/my-data")//record,
    function($div) {
        $div/@date/xs:dateTime(.)
    }
)

Example for using the index in a query, assuming $hits are records returned by a lucene full text search:

for $hit in $hits
order by memsort:get("record-date", $hit) ascending empty greatest, ft:score($hit) descending
return
    $hit

This will first sort by date, then by full text match score. Records without date will appear at the end (due to "empty greatest").

Building

If you want to create an EXPath Package for the app, you can run:

$ mvn package

There will be a .xar file in the target/ sub-folder.