ArrayAgg.php

<?php

namespace AppBundle\DoctrineExtensions\Postgres;

use Doctrine\ORM\Query\AST\Functions\FunctionNode;
use Doctrine\ORM\Query\Lexer;

/**
 *
 */
class ArrayAgg extends FunctionNode
{

    public $field;

    /**
     *  @override
     */
    public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
    {
        return "array_agg(" . $sqlWalker->walkArithmeticPrimary($this->field) . ")";
    }

    public function parse(\Doctrine\ORM\Query\Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);
        $this->field = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }

}

ArrayToJson.php

<?php

namespace AppBundle\DoctrineExtensions\Postgres;

use Doctrine\ORM\Query\AST\Functions\FunctionNode;
use Doctrine\ORM\Query\Lexer;

/**
 *
 */
class ArrayToJson extends FunctionNode
{

    public $field;

    /**
     *  @override
     */
    public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
    {
        return "array_to_json(" . $sqlWalker->walkArithmeticPrimary($this->field) . ")";
    }

    public function parse(\Doctrine\ORM\Query\Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);
        $this->field = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }

}

config.yml

orm:
  auto_generate_proxy_classes: "%kernel.debug%"
  naming_strategy: doctrine.orm.naming_strategy.underscore
  auto_mapping: true
  dql:
      string_functions:
          ARRAYAGG: AppBundle\DoctrineExtensions\Postgres\ArrayAgg
          ARRAYTOJSON: AppBundle\DoctrineExtensions\Postgres\ArrayToJson

UserRepository.php

<?php

namespace AppBundle\Repository;

use Doctrine\ORM\EntityRepository;

/**
 * UserRepository
 *
 * This class was generated by the Doctrine ORM. Add your own custom
 * repository methods below.
 */
class UserRepository extends EntityRepository
{

    /**
     * Method return all users for admin
     * @return array
     */
    public function getArrayForAdminList()
    {
        $qb = $this->createQueryBuilder('u')
                ->select(
                        'u.id AS HIDDEN id, u.roles, u.firstName, u.lastName, u.email, u.created, u.updated, u.isNewsletter, ARRAYTOJSON(ARRAYAGG(s.title)) AS user_school_title, ARRAYTOJSON(ARRAYAGG(sbj.title)) AS user_subject_title'
                )
                ->leftJoin('u.userSchools', 'usql')
                ->leftJoin('usql.school', 's')
                ->leftJoin('usql.userSchoolSubjects', 'usbj')
                ->leftJoin('usbj.subject', 'sbj')
                ->addGroupBy('u.id');

        $aResult = $qb->getQuery()->getArrayResult();
        $newResult = [];

        foreach ($aResult as $result) {
            $aTmp = [];
            foreach ($result as $key => $value) {
                if ($this->isJSON($value)) {
                    $aTmp[$key] = implode(',', json_decode($value));
                } else {
                    $aTmp[$key] = $value;
                }
            }
            $newResult[] = $aTmp;
        }

        return $newResult;
    }

    private function isJSON($string)
    {
        return is_string($string) && is_array(json_decode($string, true)) && (json_last_error() == JSON_ERROR_NONE) ? true : false;
    }

}