Fail to unpickle PickleType

[baely]

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Environment details

• Programming language: Python 3.13
• OS: MacOS 15
• Language runtime version:
• Package version: 1.10.0

Steps to reproduce

1. Define class with column of type sqlalchemy PickleType
2. Add instance of class to Spanner
3. Attempt to read the row

Sample:

import os

from sqlalchemy import Column, Integer, String, PickleType, create_engine
from sqlalchemy.orm import DeclarativeBase, Session

class Base(DeclarativeBase):
    pass

class UserPreferences(Base):
    __tablename__ = 'user_preferences'
    
    user_id = Column(Integer, primary_key=True)
    username = Column(String(50), nullable=False)
    preferences = Column(PickleType, nullable=True)
    created_at = Column(String(30), nullable=False)


os.environ["SPANNER_EMULATOR_HOST"] = "localhost:9010"
engine = create_engine("spanner+spanner:///projects/test-project/instances/test-instance/databases/test-database")

with Session(engine) as session:
    new_user = UserPreferences(
        user_id=1,
        username='test_user',
        preferences={
            'setting': 'true'
        },
        created_at="2025-05-04T00:00:00.000000"
    )

    session.add(new_user)
    session.commit()

    user = session.query(UserPreferences).filter_by(user_id=1).first()

Will raise an exception on the last line: _pickle.UnpicklingError: pickle data was truncated

The data is being base64 encoded on the way out from Spanner where SQLAlchemy is expecting raw bytes for pickled data. The data is stored as raw bytes in Spanner but being encoded on the way out.

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Thanks!