PagesSum.module

<?php

class PagesSum extends WireData implements Module {

    public static function getModuleInfo() {

        return array(
            'title'    => 'Pages Sum',
            'version'  => '1.0.0',
            'summary'  => 'Adds a $pages->sum($selectorString, $fieldName) method to sum the value of a specific field over a list of pages selected by a selector string.',
            'singular' => true,
            'autoload' => true,
            'author'   => 'ESRCH',
            'href'     => 'https://processwire.com/talk/topic/8524-creating-a-fast-pages-sum-function/?do=findComment&comment=82519',
            'requires' => 'ProcessWire>2.7.0',
        );
    }

    public function init() {
        $this->addHook('Pages::sum', function ($event) {
            $selectorString = $event->arguments(0);
            $fieldName = $event->arguments(1);

            // Find all the pages associated with the selector string
            $pageFinder = new PageFinder();
            $idQuery = $pageFinder->findIDs(new Selectors($selectorString), array('returnQuery' => true));
            $idQuery->set('orderby', array());
            $idQuery->set('groupby', array());
            $idQuery->set('limit', array());
            $stmt = $idQuery->execute();
            $idArray = $stmt->fetchAll(PDO::FETCH_COLUMN);
            // If no pages were found, return 0
            if (count($idArray) == 0) {
                $event->return = 0;
                return;
            }
            $idString = implode(',', $idArray);

            // Get the table name for the given field name
            $field = $this->fields->get($fieldName);
            // If no field with this name is found, return 0;
            if (!$field) {
                $event->return = 0;
                return;
            }
            $tableName = $field->getTable();

            // Run the SUM query
            $sumQuery = new DatabaseQuerySelect();
            $sumQuery->select("SUM(data)");
            $sumQuery->from($tableName);
            $sumQuery->where("pages_id IN ($idString)");
            $stmt2 = $sumQuery->execute();
            list($total) = $stmt2->fetch(PDO::FETCH_NUM);

            $event->return = $total;
        });
    }

}