Search solr using custom code

Drupal: Solrsearch.php

<?php

/**
 * Good resources.
 *
 * https://www.triquanta.nl/blog/what-fq-short-summary-solr-query-fields
 * https://lucene.apache.org/solr/guide/6_6/common-query-parameters.html
 * http://valuebound.com/resources/blog/how-to-create-custom-solr-search-autocomplete-drupal-7
 */

// Initializes solr, gets connection and cookie, etc.
$solr = apachesolr_get_solr();

// Create search object.
$s_query = apachesolr_drupal_query('custom', array('q' => 'something'));

// The bundle which you want to search.
$s_query->addFilter('bundle', 'course');
$s_query->setSolrsort('sort_label', 'asc');
$s_query->addParam('start', $offset);
$s_query->addParam('rows', $limit);

// Include debug information about returned info.
$s_query->addParam('debug', 'results');

// Only search in title.
$s_query->addParam('qf', 'label');


$response = $s_query->search();
$data = json_decode($response->data);
$found_courses = $data->response->docs;

dpm($found_courses);