validate :ensure_pdh_matches_manifest_text
validate :ensure_storage_classes_desired_is_not_empty
validate :ensure_storage_classes_contain_non_empty_strings
validate :versioning_metadata_updates, on: :update
validate :past_versions_cannot_be_updated, on: :update
validate :ensure_pdh_matches_manifest_text
validate :ensure_storage_classes_desired_is_not_empty
validate :ensure_storage_classes_contain_non_empty_strings
validate :versioning_metadata_updates, on: :update
validate :past_versions_cannot_be_updated, on: :update