While converting a complex AppEngine code base from python 2.7 to python 3.x, I ran into an unexpected bug in the new google.cloud.ndb that does not exist in the legacy google.appengine.ext.ndb.

Environment details

python-ndb 1.11.1
Python 2.7.18
Discovered and tested on MacOS 12.6

Steps to reproduce

See the toy example below. But to summarize: A repeated StructuredProperty that contains a compressed JsonProperty field. The bug probably apples to other property types that inherit from BlobProperty.

Code example

        from google.cloud import ndb

        class SomeStructuredProperty(ndb.Model):
            compressed_json = ndb.JsonProperty(compressed=True)

        class ParentModel(ndb.Model):
            repeated_sp = ndb.StructuredProperty(SomeStructuredProperty, repeated=True)

        m = ParentModel(repeated_sp=[SomeStructuredProperty(compressed_json={})])

        m.put()  # Raises AttributeError with google.cloud.ndb

Stack trace

Traceback (most recent call last):
  File "/.../test.py", line 247, in test_problem
    m.put()  # Raises AttrbuteError with google.cloud.ndb
  File "/.../lib/google/cloud/ndb/_options.py", line 102, in wrapper
    return wrapped(*pass_args, **kwargs)
  File "/.../lib/google/cloud/ndb/utils.py", line 121, in wrapper
    return wrapped(*args, **new_kwargs)
  File "/.../lib/google/cloud/ndb/utils.py", line 153, in positional_wrapper
    return wrapped(*args, **kwds)
  File "/.../lib/google/cloud/ndb/model.py", line 5383, in _put
    return self._put_async(_options=kwargs["_options"]).result()
  File "/.../lib/google/cloud/ndb/tasklets.py", line 214, in result
    self.check_success()
  File "/.../lib/google/cloud/ndb/tasklets.py", line 161, in check_success
    raise self._exception
AttributeError: 'list' object has no attribute 'startswith'

Possible fix?

The exception actually happens in BlobProperty._to_datastore, but under python 2.7 the stack trace doesn't show the original stack trace. If I understand that method properly, it checks self._repeated, but it neglects the repeated input argument when determining how to mutate or read the data dict that it is constructing for datastore. The exception is raised because the field itself is not self._repeated, but it is part of a repeated StructuredProperty.