trait EntityFieldDefinitionTrait

trait EntityFieldDefinitionTrait {
    
    /**
     * Gets the field definition from a specific entity base field.
     *
     * The method takes the field ID as an argument and returns the field storage
     * definition to be used in getIds() by querying the destination entity base
     * field definition.
     *
     * @param string $key
     *   The field ID key.
     *
     * @return array
     *   An associative array with a structure that contains the field type, keyed
     *   as 'type', together with field storage settings as they are returned by
     *   FieldStorageDefinitionInterface::getSettings().
     *
     * @see \Drupal\Core\Field\FieldStorageDefinitionInterface::getSettings()
     */
    protected function getDefinitionFromEntity($key) {
        $plugin_id = $this->getPluginId();
        $entity_type_id = $this->getEntityTypeId($plugin_id);
        
        /** @var \Drupal\Core\Field\FieldStorageDefinitionInterface[] $definitions */
        $definitions = $this->entityFieldManager
            ->getBaseFieldDefinitions($entity_type_id);
        $field_definition = $definitions[$key];
        return [
            'type' => $field_definition->getType(),
        ] + $field_definition->getSettings();
    }
    
    /**
     * Finds the entity type from configuration or plugin ID.
     *
     * @param string $plugin_id
     *   The plugin ID.
     *
     * @return string
     *   The entity type.
     */
    protected static function getEntityTypeId($plugin_id) {
        $entity_type_id = NULL;
        if (strpos($plugin_id, static::DERIVATIVE_SEPARATOR)) {
            list(, $entity_type_id) = explode(static::DERIVATIVE_SEPARATOR, $plugin_id, 2);
        }
        return $entity_type_id;
    }

}