interface EntityStorageSchemaInterface

interface EntityStorageSchemaInterface extends EntityTypeListenerInterface {
    
    /**
     * Checks if the changes to the entity type requires storage schema changes.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The updated entity type definition.
     * @param \Drupal\Core\Entity\EntityTypeInterface $original
     *   The original entity type definition.
     *
     * @return bool
     *   TRUE if storage schema changes are required, FALSE otherwise.
     */
    public function requiresEntityStorageSchemaChanges(EntityTypeInterface $entity_type, EntityTypeInterface $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
     * requiresEntityStorageSchemaChanges() checks. Rather, the meaning of what
     * this function returns when requiresEntityStorageSchemaChanges() returns
     * FALSE is undefined. Callers are expected to only call this function when
     * requiresEntityStorageSchemaChanges() is TRUE.
     *
     * This function can return FALSE if any of these conditions apply:
     * - There are no existing entities for the entity type.
     * - There are existing entities, but the schema changes can be applied
     *   without losing their data (e.g., if the schema changes can be performed
     *   by altering tables rather than dropping and recreating them).
     * - The only entity data that would be lost are ones that are not valid for
     *   the new definition (e.g., if changing an entity type 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\Entity\EntityTypeInterface $entity_type
     *   The updated entity type definition.
     * @param \Drupal\Core\Entity\EntityTypeInterface $original
     *   The original entity type definition.
     *
     * @return bool
     *   TRUE if data migration is required, FALSE otherwise.
     *
     * @see self::requiresEntityStorageSchemaChanges()
     */
    public function requiresEntityDataMigration(EntityTypeInterface $entity_type, EntityTypeInterface $original);

}