interface DynamicallyFieldableEntityStorageSchemaInterface

interface DynamicallyFieldableEntityStorageSchemaInterface extends EntityStorageSchemaInterface, FieldStorageDefinitionListenerInterface {
    
    /**
     * Checks if the changes to the storage definition requires schema changes.
     *
     * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition
     *   The updated field storage definition.
     * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $original
     *   The original field storage definition.
     *
     * @return bool
     *   TRUE if storage schema changes are required, FALSE otherwise.
     */
    public function requiresFieldStorageSchemaChanges(FieldStorageDefinitionInterface $storage_definition, FieldStorageDefinitionInterface $original);
    
    /**
     * Checks if existing data would be lost if the schema changes were applied.
     *
     * If there are no schema changes needed, then no data needs to be migrated,
     * but it is not the responsibility of this function to recheck what
     * requiresFieldStorageSchemaChanges() checks. Rather, the meaning of what
     * this function returns when requiresFieldStorageSchemaChanges() returns
     * FALSE is undefined. Callers are expected to only call this function when
     * requiresFieldStorageSchemaChanges() is TRUE.
     *
     * This function can return FALSE if any of these conditions apply:
     * - There are no existing entities for the entity type to which this field
     *   is attached.
     * - There are existing entities, but none with existing values for this
     *   field.
     * - There are existing field values, but the schema changes can be applied
     *   without losing them (e.g., if the schema changes can be performed by
     *   altering tables rather than dropping and recreating them).
     * - The only field values that would be lost are ones that are not valid for
     *   the new definition (e.g., if changing a field from revisionable to
     *   non-revisionable, then it's okay to drop data for the non-default
     *   revision).
     *
     * When this function returns FALSE, site administrators will be unable to
     * perform an automated update, and will instead need to perform a site
     * migration or invoke some custom update process.
     *
     * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition
     *   The updated field storage definition.
     * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $original
     *   The original field storage definition.
     *
     * @return bool
     *   TRUE if data migration is required, FALSE otherwise.
     *
     * @see self::requiresFieldStorageSchemaChanges()
     */
    public function requiresFieldDataMigration(FieldStorageDefinitionInterface $storage_definition, FieldStorageDefinitionInterface $original);
    
    /**
     * Performs final cleanup after all data of a field has been purged.
     *
     * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition
     *   The field being purged.
     */
    public function finalizePurge(FieldStorageDefinitionInterface $storage_definition);

}