postgresql - Use deferred reflection in SQLAlchemy 0.7 with cached metadata -

in project delaretive base deferred reflection being used.

from sqlalchemy import (     create_engine, table, column, integer, biginteger, text, datetime, numeric, string, )  sqlalchemy.dialects.postgresql import cidr sqlalchemy.orm import mapper, sessionmaker, relationship, backref sqlalchemy.orm.mapper import configure_mappers sqlalchemy.orm.util import _is_mapped_class sqlalchemy.pool import nullpool, queuepool sqlalchemy.ext.declarative import declarative_base, declared_attr sqlalchemy.schema import sequence sqlalchemy.ext.hybrid import hybrid_property   # class taken sqlalchemy recipes class declarativereflectedbase(object):      _mapper_args = []      @classmethod     def __mapper_cls__(cls, *args, **kw):         cls._mapper_args.append((args, kw))      @classmethod     def prepare(cls, engine):         while cls._mapper_args:             args, kw = cls._mapper_args.pop()             klass = args[0]              if args[1] not none:                 table = args[1]                 table(table.name,                       cls.metadata,                       extend_existing=true,                       autoload_replace=false,                       autoload=true,                       autoload_with=engine,                       schema=table.schema)              c in klass.__bases__:                 if _is_mapped_class(c):                     kw['inherits'] = c                     break              klass.__mapper__ = mapper(*args, **kw)   base = declarative_base()   class reflected(declarativereflectedbase, base):      __abstract__ = true   class customer(reflected):      @declared_attr     def __tablename__(cls):         return "customer"      __table_args__ = {"schema": "schema_customer"}      id = column('id', integer, primary_key=true)     balances = relationship(lambda: balance, backref="customer")   class balance(reflected):      @declared_attr     def __tablename__(cls):         return "balance"      __table_args__ = {"schema": "billing"}      id = column('id', integer, primary_key=true)     currency = relationship(lambda: currency)      @hybrid_property     def name_with_currency(self):         return "{0} ({1})".format(self.name, self.currency.name_short)      @name_with_curr.expression     def name_with_curr_expr(cls):         return cls.name + " (" + currency.name_short + ")"  .......  # , other classes below   def orm_initialization(engine):     reflected.prepare(engine)  # reflect db tables metadata      s = sessionmaker()     s = s(bind=engine)      try:         contetxs_count = s.query(contexts).count()          # other classes difine not constant number of postgresql database contexts         ....         # call prepare again         reflected.prepare(engine)     finally:         s.close()   def sessionmaker_get(host, port, dbname, user, password, existing_engine=none, pooling=false):     if existing_engine none:         engine = create_engine(             "{dialect}://{user}:{password}@{host}:{port}/{dbname}"             .format(dialect="postgresql", **locals()),             poolclass=nullpool,             echo=false         )     else:         engine = existing_engine      orm_initialization(engine)      s = sessionmaker(bind=engine)     return s 

this works ok initialization of orm takes 7-8 seconds. so, want cache pickled metadata in file , load when create new sessionmaker. store metadata file on hdd , tried connect metadata reflected before first call prepare().

def orm_initialization(engine):      import cpickle     open('/tmp/metadata') meta_file:         meta = cpickle.load(meta_file)         meta.bind = engine     reflected.metadata = meta      reflected.prepare(engine)  # reflect db tables metadata      s = sessionmaker()     s = s(bind=engine)     .... 

but error

argumenterror: not determine join condition between parent/child tables on relationship ... specify 'primaryjoin' expression. if 'secondary' present, 'secondaryjoin' needed well.

what doing wrong? how load pickled metadata correctly?