BlogController.php

<?php

namespace Drupal\blog\Controller;

use Symfony\Component\HttpFoundation\Response;

use Drupal\Core\Controller\ControllerBase;

/**
 * Controller class for the blog module.
 */
class BlogController extends ControllerBase {

    public function index()
    {
        $query = db_select('node_field_data', 'nfd');
        $query->join('node__body', 'nb', 'nfd.nid = nb.entity_id');
        $query->join('node__field_date', 'nfdate', 'nfd.nid = nfdate.entity_id');
        $query->join('node__field_image', 'nfi', 'nfd.nid = nfi.entity_id');
        $query->join('node__field_category', 'nfcat', 'nfd.nid = nfcat.entity_id');
        $query->join('file_managed', 'fm', 'nfi.field_image_target_id = fm.fid');

        $query->addField('fm', 'uri', 'image');
        $query->addField('nfdate', 'field_date_value', 'date');
        $query->addField('nfcat', 'field_category_value', 'category');

        $query
            ->fields('nb', array('body_value', 'body_summary'))
            ->fields('nfd', array('nid', 'title', 'created'))
            ->condition('nb.bundle', 'blog_post', '=')
            ->range(0, 50);

        $posts = $query->execute();
        $result = \Drupal::service('twig')
            ->loadTemplate(drupal_get_path('module', 'blog') . '/templates/blog-index' . twig_extension())
            ->render(['posts' => $posts]);

        return $result;

        // return new Response($result);

        // return array(
        //     array(
        //         '#theme' => 'blog_index',
        //         '#posts' => $posts,
        //     ),
        // );
    }
}