Example of how to create a custom search feature for the Bolt CMS, by making a local extension

ExampleSearchExtension.php

<?php

namespace Bolt\Extension\DesignSpike\ExampleSearch;

use Bolt\Extension\SimpleExtension;
use Bolt\Routing\ControllerCollection;
use Doctrine\DBAL\Query\QueryBuilder;
use Silex\Application;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

class ExampleSearchExtension extends SimpleExtension
{
    protected function registerFrontEndRoutes(ControllerCollection $collection)
    {
        $collection->get('/search', [$this, 'callbackProductSearch']);
    }
    protected function callbackProductSearch(Application $app, Request $request)
    {
        $number   = trim($request->query->get('number'));
        $name     = trim($request->query->get('name'));
        $cas      = trim($request->query->get('cas'));
        $formula  = trim($request->query->get('formula'));
        $general  = trim($request->query->get('q'));

        $results = [];

        if ($number or $name or $cas or $formula or $general) {
            $repo = $app['storage']->getRepository('products');
            /** @var $qb QueryBuilder */
            $qb = $repo->createQueryBuilder();
        }
        // search for the provided word in any of the main fields
        if ($general) {
            $qb->orWhere("number LIKE CONCAT('%', :general, '%')");
            $qb->orWhere("cas    LIKE CONCAT('%', :general, '%')");
            $qb->setParameter('general', $general);

            // get an array of all words entered in the visitor's search
            $terms = array_filter(array_map('trim', explode(' ', $general)));

            // name - search for items where every word in the search is found in the name field
            $nameAndX = $qb->expr()->andX();
            foreach ($terms as $index => $term) {
                $param_name = "term".$index;
                $nameAndX->add("name LIKE CONCAT('%', :".$param_name.", '%')");
                $qb->setParameter($param_name, $term);
            }
            $qb->orWhere($nameAndX);

            // synonyms - search for items where every word in the search is found in the synonyms field
            $synonymsAndX = $qb->expr()->andX();
            foreach ($terms as $index => $term) {
                $param_name = "term".$index;
                $synonymsAndX->add("synonyms LIKE CONCAT('%', :".$param_name.", '%')");
                $qb->setParameter($param_name, $term);
            }
            $qb->orWhere($synonymsAndX);
        }
        if ($number) {
            $qb->andWhere("number LIKE CONCAT('%', :number, '%')");
            $qb->setParameter('number', $number);
        }
        if ($name) {
            // this is where we should start the stuff about synonyms
            $terms = array_filter(array_map('trim', explode(' ', $name)));
            foreach ($terms as $index => $term) {
                $param_name = "nameterm".$index;
                $qb->andWhere("name LIKE CONCAT('%', :".$param_name.", '%') OR synonyms LIKE CONCAT('%', :".$param_name.", '%')");
                $qb->setParameter($param_name, $term);
            }
        }
        if ($cas) {
            $qb->andWhere("cas LIKE CONCAT('%', :cas, '%')");
            $qb->setParameter('cas', $cas);
        }
        if ($formula) {
            // search for chemical formula - in mysql this requires binary search for case sensitivity
            $qb->andWhere("formula REGEXP BINARY
                CONCAT(
                    '(>|[[:<:]]|[[:lower:]]|[[:upper:]]|[[:digit:]]|\\\(|\\\))',
                    :formula,
                    '(<|[[:>:]]|[[:upper:]]|[[:digit:]]|\\\(|\\\))'
                )");
            // ensure that user-inputted special characters aren't parsed as regex characters
            $escaped_formula = preg_quote($formula);
            $qb->setParameter('formula', $escaped_formula);
        }
        if (isset($qb)) {
            $results = $qb->execute()->fetchAll();
        }

        $html = $app['twig']->render('product_search.twig', [
            'results'  => $results
        ]);
        return new Response($html);
    }
}