Test case for error described in http://www.monkinetic.com/2013/08/07/sqlalchemy-property-exists-on-mapper. IN this case, the error does not occur.

test_sqlalchemy_relationship.py

import sys
import os

sys.path.append(os.path.abspath('.'))
sys.path.append(os.path.abspath('markbox'))
print sys.path

# from markbox.models import UserBlogSettings

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, scoped_session, relationship
import sqlalchemy as sa

SQLALCHEMY_DATABASE_URI = "sqlite:///:memory:"

engine = create_engine(SQLALCHEMY_DATABASE_URI, echo='debug')
db_session_maker = scoped_session(sessionmaker(autocommit=False,
  autoflush=False,
  bind=engine))
session = db_session_maker()

Base = declarative_base()
Base.query = db_session_maker.query_property()

class UserBlogSettings(Base):
    __tablename__ = 'user_blogsettings'

    id = sa.Column(sa.Integer, primary_key=True)
    uid = sa.Column(sa.String(256))
    # blog title

     # returns a query => blog.sync_stats.all()
    sync_stats = relationship('SyncStats', backref='blog')


class SyncStats(Base):
    """
    Store various statistics about sync operations
    """
    __tablename__ = 'system_syncstats'

    id = sa.Column(sa.Integer, primary_key=True)

    uid = sa.Column(sa.String(256), sa.ForeignKey('user_blogsettings.uid'))


def main():
    Base.metadata.create_all(engine)
    q = UserBlogSettings.query.limit(1)

if __name__ == '__main__':
    main()