Example of how not to use Oro Search Bundle for Auto-completion field (Data Flow: services.yml > MyFormType.php > AutocompleteController.php > Helper.php)

AutocompleteController.php

<?php

// src/Acme/Bundle/AcmeBundle/Controller/AutocompleteController.php

namespace Acme\Bundle\AcmeBundle\Controller;

use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
use Symfony\Component\HttpKernel\Exception\HttpException;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\JsonResponse;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;

use Oro\Bundle\SecurityBundle\Annotation\AclAncestor;

use Oro\Bundle\FormBundle\Autocomplete\Security;
use Oro\Bundle\FormBundle\Autocomplete\SearchHandlerInterface;

use Acme\Bundle\AcmeBundle\Helper\Helper;

/**
 * @Route("/acme-autocomplete")
 */
class AutocompleteController extends Controller
{
    /* @var string */
    private $name;
    /* @var string */
    private $query;
    /* @var integer */
    private $page;
    /* @var integer */
    private $perPage;
    /* @var boolean */
    private $searchById;

    private function validate(Request $request)
    {
        $this->name       = $request->get('name');
        $this->query      = $request->get('query');
        $this->page       = intval($request->get('page', 1));
        $this->perPage    = intval($request->get('per_page', 50));
        $this->searchById = (bool) $request->get('search_by_id', false);

        if ( ! $this->name) {
            throw new HttpException(400, 'Parameter "name" is required');
        }

        if ($this->page <= 0) {
            throw new HttpException(400, 'Parameter "page" must be greater than 0');
        }

        if ($this->perPage <= 0) {
            throw new HttpException(400, 'Parameter "per_page" must be greater than 0');
        }

        if ( ! $this->get('oro_form.autocomplete.security')->isAutocompleteGranted($this->name)) {
            throw new AccessDeniedHttpException('Access denied.');
        }
    }

    /**
     * @Route("/category", name="acme_form_autocomplete")
     * AclAncestor("acme_category_view")
     */
    public function searchCategoryAction(Request $request)
    {
        $this->validate($request);

        /** @var Helper $helper */
        $helper = $this->get('acme.helper');

        return new JsonResponse($helper->getMyCategories($this->query, $this->page, $this->perPage, $this->searchById));
    }
}

Helper.php

<?php

// src/Acme/Bundle/AcmeBundle/Helper/Helper.php

namespace Acme\Bundle\AcmeBundle\Helper;

use Symfony\Component\DependencyInjection\ContainerInterface as Container;

use Doctrine\ORM\EntityRepository;

use Doctrine\ORM\Query;
use Doctrine\ORM\QueryBuilder;
use Doctrine\ORM\Query\Parameter;
use Doctrine\ORM\Query\Expr;
use Doctrine\ORM\Query\Expr\Andx;

use Oro\Bundle\UserBundle\Entity\User;
use Acme\Bundle\AcmeBundle\Entity\Acme;

class Helper
{
    private $container;

    public function __construct(Container $container) {
        $this->container = $container;
    }

    /**
     * Generate data for Autocompletion request
     *
     * Usage 1:
     * return $this->arrayAutoComplete($page, $perPage, $query);
     *
     * Usage 2:
     * return $this->arrayAutoComplete($page, $perPage, $query, function($results) {
     *     $result = array();
     *     foreach ($results as $data) {
     *         $result[] = array(
     *             'id' => $data['id'],
     *             'name' => $data['code'] . ': ' . $data['name'],
     *         );
     *     }
     *     return $result;
     * });
     *
     * @param integer $page
     * @param integer $perPage
     * @param QueryBuilder $query
     * @param callable $func
     *
     * @return array
     */
    public function arrayAutoComplete($page, $perPage, $query, callable $func = null) {

        $page = (int) $page > 0 ? (int) $page : 1;
        $perPage = (int) $perPage > 0 ? (int) $perPage : 10;
        $firstResult = ($page - 1) * $perPage;

        $query->setMaxResults($perPage);
        $query->setFirstResult($firstResult);

        // Convert Parameters to simple array to debug easier
        $params = $query->getParameters();
        $paramsDebug = array();
        foreach ($params as $p) {
            $paramsDebug[$p->getName()] = $p->getValue();
        }

        // var_dump(array('DQL' => $query->getDQL(), 'Params' => $paramsDebug));

        $results = $query->getQuery()->getArrayResult();

        $more = count($results) == $perPage;
        if ($more) {
            $results = array_slice($results, 0, $perPage);
        }

        if (is_null($func)) {
            $result = array();
            foreach ($results as $data) {
                $result[] = array(
                    'id' => $data['id'],
                    'name' => $data['name'],
                );
            }
        } else {
            $result = $func($results);
        }

        /*
        return array(
            'results' => $result,
            'more' => $more,
            'dql' => $query->getDQL(),
            'max_result' => $perPage,
            'first_result' => $firstResult,
            'params' => $paramsDebug,
        );
        */
        return array(
            'results' => $result,
            'more' => $more,
        );
    }

    /**
     * Get Category List for Current User
     */
    public function getMyCategories($queryString, $page, $perPage, $searchById) {

        $doctrine = $this->getDoctrine();

        /* @var User $user */
        $user = $this->getUser();

        /* @var EntityRepository $repository */
        $repository = $doctrine->getRepository('AcmeBundle:Acme');
        /* @var QueryBuilder $query */
        $query = $repository->createQueryBuilder('a');

        // Your custom logic here
        // $query->xxxx();

        return $this->arrayAutoComplete($page, $perPage, $query);
    }

    /**
     * Dump data with \Doctrine\Common\Util\Debug::dump()
     *
     * @param data
     */
    function dump($var, $maxDepth = 2, $stripTags = true) {
        \Doctrine\Common\Util\Debug::dump($var, $maxDepth, $stripTags);
    }

    /**
     * The following methods are copied from Symfony\Bundle\FrameworkBundle\Controller\Controller
     */
    public function getRequest()
    {
        return $this->container->get('request');
    }

    public function getDoctrine()
    {
        if (!$this->container->has('doctrine')) {
            throw new \LogicException('The DoctrineBundle is not registered in your application.');
        }

        return $this->container->get('doctrine');
    }

    public function getUser()
    {
        if (!$this->container->has('security.context')) {
            throw new \LogicException('The SecurityBundle is not registered in your application.');
        }

        if (null === $token = $this->container->get('security.context')->getToken()) {
            return null;
        }

        if (!is_object($user = $token->getUser())) {
            return null;
        }

        return $user;
    }

    public function has($id)
    {
        return $this->container->has($id);
    }

    public function get($id)
    {
        return $this->container->get($id);
    }
}

MyFormType.php

<?php

// src/Acme/Bundle/AcmeBundle/Form/Type/MyFormType.php

namespace Acme\Bundle\AcmeBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

use Atf\Bundle\QuotesBundle\Form\EventListener\QuoteSubscriber;
use Atf\Bundle\QuotesBundle\Helper\Helper;

class MyFormType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array                $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add(
                'category',
                'oro_jqueryselect2_hidden',
                array(
                    'autocomplete_alias' => 'acme_autocomplete',
                    'required' => false,
                    'configs' => array(
                        'placeholder' => 'Select Category (as Category is example field here)',
                        /**
                         * "acme_form_autocomplete" is in:
                         * Acme\Bundle\AcmeBundle\Controller\AutocompleteController
                         */
                        'route_name' => 'acme_form_autocomplete',
                    ),
                    'label' => 'Category'
                )
            );

services.yml

#
# src/Acme/Bundle/AcmeBundle/Resources/config/services.yml
#
parameters:
    acme.helper.class: Acme\Bundle\AcmeBundle\Helper\Helper
    acme.entity.class: Acme\Bundle\AcmeBundle\Entity\Acme
services:
    #
    # Helper class to do the custom business logic
    #
    acme.helper:
        class: %acme.helper.class%
        arguments: ['@service_container']
    #
    # Search Handler for Autocomplete
    #
    # Re-declaring the containier class "oro_form.autocomplete.search_handler" without "calls" parameter
    # as new container service so that the Search Bundle related logic is not called
    # and that let us avoid having to create the file "search.yml" and its associated data for search fuctionality
    # (which I don't need)
    #
    # (The original container class "oro_form.autocomplete.search_handler" is found at:
    #  vendor/oro/platform/src/Oro/Bundle/FormBundle/Resources/config/autocomplete.yml)
    #
    acme_form.autocomplete.search_handler:
        class: %oro_form.autocomplete.search_handler.class%
        abstract: true
    #
    # Specify this service in Form Type Class
    #
    acme.form.autocomplete.search_handler:
        parent: acme_form.autocomplete.search_handler
        arguments:
            - %acme.entity.class%
            - [name]
        tags:
            - { name: oro_form.autocomplete.search_handler, alias: acme_autocomplete, acl_resource: acme_view }