class EntityReference

class EntityReference extends DisplayPluginBase {
  
  /**
   * {@inheritdoc}
   */
  protected $usesAJAX = FALSE;
  
  /**
   * {@inheritdoc}
   */
  protected $usesPager = FALSE;
  
  /**
   * {@inheritdoc}
   */
  protected $usesAttachments = FALSE;
  
  /**
   * The database connection.
   *
   * @var \Drupal\Core\Database\Connection
   */
  protected $connection;
  
  /**
   * Constructs a new EntityReference object.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Database\Connection $connection
   *   The database connection.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, Connection $connection) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->connection = $connection;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('database'));
  }
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    // Force the style plugin to 'entity_reference_style' and the row plugin to
    // 'fields'.
    $options['style']['contains']['type'] = [
      'default' => 'entity_reference',
    ];
    $options['defaults']['default']['style'] = FALSE;
    $options['row']['contains']['type'] = [
      'default' => 'entity_reference',
    ];
    $options['defaults']['default']['row'] = FALSE;
    // Set the display title to an empty string (not used in this display type).
    $options['title']['default'] = '';
    $options['defaults']['default']['title'] = FALSE;
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function optionsSummary(&$categories, &$options) {
    parent::optionsSummary($categories, $options);
    // Disable 'title' so it won't be changed from the default set in
    // \Drupal\views\Plugin\views\display\EntityReference::defineOptions.
    unset($options['title']);
  }
  
  /**
   * {@inheritdoc}
   */
  public function getType() {
    return 'entity_reference';
  }
  
  /**
   * {@inheritdoc}
   */
  public function execute() {
    return $this->view
      ->render($this->display['id']);
  }
  
  /**
   * Builds the view result as a renderable array.
   *
   * @return array
   *   Renderable array or empty array.
   */
  public function render() {
    if (!empty($this->view->result) && $this->view->style_plugin
      ->evenEmpty()) {
      return $this->view->style_plugin
        ->render($this->view->result);
    }
    return [];
  }
  
  /**
   * {@inheritdoc}
   */
  public function usesExposed() {
    return FALSE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function query() {
    if (!empty($this->view->live_preview)) {
      return;
    }
    // Make sure the id field is included in the results.
    $id_field = $this->view->storage
      ->get('base_field');
    $id_table = $this->view->storage
      ->get('base_table');
    $this->id_field_alias = $this->view->query
      ->addField($id_table, $id_field);
    $options = $this->getOption('entity_reference_options');
    // Restrict the autocomplete options based on what's been typed already.
    if (isset($options['match'])) {
      $style_options = $this->getOption('style');
      $value = $this->connection
        ->escapeLike($options['match']);
      if ($options['match_operator'] !== '=') {
        $value = $value . '%';
        if ($options['match_operator'] != 'STARTS_WITH') {
          $value = '%' . $value;
        }
      }
      // Multiple search fields are OR'd together.
      $conditions = new Condition('OR');
      // Build the condition using the selected search fields.
      foreach ($style_options['options']['search_fields'] as $field_id) {
        if (!empty($field_id)) {
          // Get the table and field names for the checked field.
          $field_handler = $this->view->field[$field_id];
          $table_alias = $this->view->query
            ->ensureTable($field_handler->table, $field_handler->relationship);
          $field_alias = $this->view->query
            ->addField($table_alias, $field_handler->realField);
          $field = $this->view->query->fields[$field_alias];
          // Add an OR condition for the field.
          $conditions->condition($field['table'] . '.' . $field['field'], $value, 'LIKE');
        }
      }
      $this->view->query
        ->addWhere(0, $conditions);
    }
    // Add an IN condition for validation.
    if (!empty($options['ids'])) {
      $this->view->query
        ->addWhere(0, $id_table . '.' . $id_field, $options['ids'], 'IN');
    }
    $this->view
      ->setItemsPerPage($options['limit']);
  }
  
  /**
   * {@inheritdoc}
   */
  public function validate() {
    $errors = parent::validate();
    // Verify that search fields are set up.
    $style = $this->getOption('style');
    if (!isset($style['options']['search_fields'])) {
      $errors[] = $this->t('Display "@display" needs a selected search fields to work properly. See the settings for the Entity Reference list format.', [
        '@display' => $this->display['display_title'],
      ]);
    }
    else {
      // Verify that the search fields used actually exist.
      $fields = array_keys($this->handlers['field']);
      foreach ($style['options']['search_fields'] as $field_alias => $enabled) {
        if ($enabled && !in_array($field_alias, $fields)) {
          $errors[] = $this->t('Display "@display" uses field %field as search field, but the field is no longer present. See the settings for the Entity Reference list format.', [
            '@display' => $this->display['display_title'],
            '%field' => $field_alias,
          ]);
        }
      }
    }
    return $errors;
  }

}