Chapter 10. Searching with the Optic API

The Optic API, introduced in MarkLogic 9, implements common relational operations over data extracted from documents. This chapter illustrates how to accomplish some common tasks, which should help in transitioning to MarkLogic from a relational background.

Paging Over Results

Problem

An Optic API query returns a large result set. Get a stable set of results a page at a time.

Solution

Applies to MarkLogic versions 9+ and higher

In its simplest form:

const op = require('/MarkLogic/optic');
const pageSize = ...;
const pageNumber = ...;

op.fromTriples([...)])
  .offsetLimit(op.param('offset'), pageSize)
  .result(null, {offset: pageSize * (pageNumber - 1)})

Expanded out to a main module, which allows the caller to specify the page and a timestamp, the recipe looks like this:

const op = require('/MarkLogic/optic');

const pageNumber =
  parseInt(xdmp.getRequestField('page', '1'), 10);
const pageSize = 1000;

let timestamp = xdmp.getRequestField('timestamp');
if (timestamp === null) {
  timestamp = xdmp.requestTimestamp();
}

const response = {
  timestamp: timestamp,
  page: pageNumber,
  results: xdmp.invokeFunction(
    function() {
      return op.fromTriples([...])
        .offsetLimit(op.param('offset'), pageSize)
        .result(null, {offset: pageSize * (pageNumber - 1)});
    },
    { timestamp: timestamp }
  )
}

response

Required Privilege

  • xdmp:timestamp

Discussion

Sometimes your result set will be bigger than you want to return in a single request. Paging solves this problem ...

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