Alters a Drupal 8 view by adding a Left Join and Where condition

Drupal8_views_query_alter.php

<?php

use Drupal\views\ViewExecutable;
use Drupal\views\Plugin\views\query\QueryPluginBase;


/**
 * Implementation of hook_views_query_alter
 * @param type $view
 * @param type $query
 */
function eclkc_customizations_views_query_alter(ViewExecutable $view, QueryPluginBase $query) {

  // This alter view is required to filter to only 'reviewed' submissions - it was not
  // possible to save the view due to a bug. 

  if ($view->id() == 'job_center') {
    $configuration = [
      'type'       => 'LEFT',
      'table'      => 'webform_submission_data',
      'field'      => 'sid',
      'left_table' => 'webform_submission',
      'left_field' => 'sid',
      'operator'   => '=',
    ];
    $join_obj = \Drupal\views\Views::pluginManager('join')
      ->createInstance('standard', $configuration);
    $rel = $query->addRelationship('webform_submission_field_job_center_posting_status', $join_obj, 'node_field_data');
    $query->addTable('webform_submission_data', $rel, $join_obj, 'webform_submission_field_job_center_posting_status');
    $join_obj->extra[] = array(
      'field'=>'name',
      'value' => 'status',
    );
    $join_obj->extra_type = 'AND';
    $query->addWhere('', 'webform_submission_field_job_center_posting_status.value', 'reviewed', 'IN');
  }
}