Question

I’m trying to shard my database into two: one for my main objects, another for logs. Right now, my code looks something like this:

engine = create_engine('postgresql+psycopg2://postgres:password@localhost:5432/logs')
engine2 = create_engine('postgresql+psycopg2://postgres:password@localhost:5432/logs')
DBSession = scoped_session(sessionmaker(extension=ZopeTransactionExtension()))
binds = {'thing': engine,
    'log': engine_a}
DBSession.configure(binds=binds)
Base = declarative_base(bind=engine)
Base2 = declarative_base(bind=engine2)

class Thing(Base):
    ...

class Log(Base2):
    ...

Where I have more tables using both Base and Base2 as well as inherited objects. I’ve also tried doing the following:

DBSession = scoped_session(sessionmaker(extension=ZopeTransactionExtension(), bind=engine))
DBSession2 = scoped_session(sessionmaker(extension=ZopeTransactionExtension(), bind=engine2))

However, using either way and only working with objects in Base, not Base2, I get the following error when querying:

return DBSession.query(cls).filter(func.lower(cls.name) == name.lower()).first()
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/scoping.py", line 113, in do
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/session.py", line 969, in query
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/query.py", line 107, in __init__
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/query.py", line 116, in _set_entities
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/query.py", line 131, in _setup_aliasizers
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/util.py", line 550, in _entity_info
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/mapper.py", line 2861, in configure_mappers
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/mapper.py", line 1166, in _post_configure_properties
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/interfaces.py", line 128, in init
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/properties.py", line 913, in do_init
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/orm/properties.py", line 969, in _process_dependent_arguments
  File "build/bdist.macosx-10.7-intel/egg/sqlalchemy/ext/declarative.py", line 1346, in return_cls
  File "<string>", line 1, in <module>
AttributeError: 'Table' object has no attribute 'id'

Of course my table has an attribute ‘id’, all the same code works as long as I only have one DBSession and one Base. What am I doing wrong?

Answer 1

I found out the problem. I simply had to initiate DBSession().