SqlAlchemy Eager Loading Example Issue

eager_loading.py

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.ext.declarative import declarative_base

def buildConnectionString(db_type, server, port, name, user, password):
    # We're using an in-memory data
    if db_type == "sqlite":
        return "sqlite://"

    authStr = user + ":" + password + "@" if user and len(user) and len(password) else ""
    # E.g. postgresql://localhost:5432/my_db
    return "{}://{}{}:{}/{}".format(db_type, authStr, server, port, name)

connectionString = buildConnectionString(\
    "postgresql",
    "localhost",
    "5432",
    "",
    "",
    None)

Base = declarative_base()

class Thing(Base):
    __tablename__ = "Things"
    id = Column(Integer, primary_key=True)
    name = Column(String(256))
    thingType = Column(String(256))
    __mapper_args__ = {
            'with_polymorphic':'*',
            'polymorphic_load':'inline',
            'polymorphic_on':"thingType",
            'polymorphic_identity':"thing"
        }


    def __init__(self, **kwds):
        for key in kwds:
            setattr(self, key, kwds[key])

class Ball(Thing):
    __tablename__ = "Balls"
    id = Column('id', Integer, ForeignKey('Things.id'), primary_key=True)
    color = Column('color', String(256))

    __mapper_args__ = {
        'polymorphic_identity':'ball'
    }

    pass

class Bin(Thing):
    __tablename__ = "Bins"
    id = Column('id', Integer, ForeignKey('Things.id'), primary_key=True)
    ballId = Column('ballId', Integer, ForeignKey('Balls.id'))
    ball = relationship(Ball, foreign_keys=[ballId], backref="outputBins")

    __mapper_args__ = {
        'polymorphic_identity':'bin'
    }
    pass

class Court(Thing):
    __tablename__ = "Courts"
    id = Column('id', Integer, ForeignKey('Things.id'), primary_key=True)
    homeBinId = Column('homeBinId', Integer, ForeignKey('Bins.id'))
    awayBinId = Column('awayBinId', Integer, ForeignKey('Bins.id'))
    homeBin = relationship(Bin, foreign_keys=[homeBinId], backref="homeCourts")
    awayBin = relationship(Bin, foreign_keys=[awayBinId], backref="awayCourts")

    __mapper_args__ = {
        'polymorphic_identity':'court'
    }


def buildTables(metadata):
    thingTable = Table(
        'Things', metadata,
        Column('id', Integer(), primary_key=True),
        Column('thingType', String(256)),
        Column('name', String(256))
    )

    ballTable = Table(
        'Balls', metadata,
        Column('id', Integer, ForeignKey(thingTable.c.id), primary_key=True),
        Column('color', String(256))
    )

    binTable = Table(
        'Bins', metadata,
        Column('id', Integer, ForeignKey(thingTable.c.id), primary_key=True),
        Column('ballId', Integer, ForeignKey(ballTable.c.id)),
    )

    courtTable = Table(
        'Courts', metadata,
        Column('id', Integer, ForeignKey(thingTable.c.id), primary_key=True),
        Column('homeBinId', Integer, ForeignKey(binTable.c.id)),
        Column('awayBinId', Integer, ForeignKey(binTable.c.id)),
    )
    return


metadata = MetaData()
engine = create_engine(connectionString)
buildTables(metadata)
Session = sessionmaker(bind=engine)
session = Session()

def initializeWithData():
    baseball = Ball(name="baseball", thingType="ball", color="white")
    bin = Bin(name="bin", thingType="bin", ball=baseball)
    court = Court(name="SomeCourt", thingType="court", homeBin=bin)
    session.add(baseball)
    session.add(bin)
    session.commit()
    return

# Uncomment the below to create the tables in the database and add some reason
#metadata.create_all(engine)
#initializeWithData()

def courtQuery():

    awayBalls = aliased(Ball, name="awayBalls")
    homeBalls = aliased(Ball, name="homeBalls")
    awayBins = aliased(Bin, name="awayBins")
    homeBins = aliased(Bin, name="homeBins")

    query = session.query(Court)\
        .outerjoin(awayBins, Court.awayBinId == awayBins.id)\
        .outerjoin(awayBalls, awayBins.ballId == awayBalls.id)\
        .outerjoin(homeBins, Court.homeBinId == homeBins.id)\
        .outerjoin(homeBalls, homeBins.ballId == homeBalls.id)\
        .options(contains_eager(Court.awayBin, alias=awayBins).contains_eager(awayBins.ball, alias=awayBalls))\
        .options(contains_eager(Court.homeBin, alias=homeBins).contains_eager(homeBins.ball, alias=homeBalls))
    return [r for r in query]

def checkData():
    import time
    timesChecked = 0

    while(True):
        print("Times checked = {}".format(timesChecked))
        results = courtQuery()
        court = results[0]
        ball = court.homeBin.ball
        ballColor = ball.color
        print(ballColor)
        print("Sleeping")
        timesChecked += 1
        time.sleep(5)
    return

checkData()