getFieldItemClass example

    // Unset static flag.     static::$inDeletion = FALSE;
  }

  /** * {@inheritdoc} */
  public function getSchema() {
    if (!isset($this->schema)) {
      // Get the schema from the field item class.       $class = $this->getFieldItemClass();
      $schema = $class::schema($this);
      // Fill in default values for optional entries.       $schema += [
        'columns' => [],
        'unique keys' => [],
        'indexes' => [],
        'foreign keys' => [],
      ];

      // Merge custom indexes with those specified by the field type. Custom       // indexes prevail.