def _from_reference(reference, app, namespace):
"""Convert Reference protobuf to :class:`~google.cloud.datastore.key.Key`.
This is intended to work with the "legacy" representation of a
datastore "Key" used within Google App Engine (a so-called
"Reference"). This assumes that ``serialized`` was created within an App
Engine app via something like ``ndb.Key(...).reference()``.
However, the actual type used here is different since this code will not
run in the App Engine standard environment where the type was
``google.appengine.datastore.entity_pb.Reference``.
Args:
serialized (bytes): A reference protobuf serialized to bytes.
app (Optional[str]): The application ID / project ID for the
constructed key.
namespace (Optional[str]): The namespace for the constructed key.
Returns:
google.cloud.datastore.key.Key: The key corresponding to
``serialized``.
Raises:
RuntimeError: If ``app`` is not :data:`None`, but not the same as
``reference.app``.
RuntimeError: If ``namespace`` is not :data:`None`, but not the same as
``reference.name_space``.
"""
project = _project_from_app(reference.app)
if app is not None:
if _project_from_app(app) != project:
raise RuntimeError(
_REFERENCE_APP_MISMATCH.format(reference.app, app)
)
parsed_namespace = _key_module._get_empty(reference.name_space, "")
if namespace is not None:
if namespace != parsed_namespace:
raise RuntimeError(
_REFERENCE_NAMESPACE_MISMATCH.format(
reference.name_space, namespace
)
)
_key_module._check_database_id(reference.database_id)
flat_path = _key_module._get_flat_path(reference.path)
return google.cloud.datastore.Key(
*flat_path, project=project, namespace=parsed_namespace
)
def _call_fut(value, empty_value):
from google.cloud.datastore.key import _get_empty
return _get_empty(value, empty_value)