My project requires querying an externally-managed database as well as a
project-specific database. What I've been doing to date is copying the
external database (which changes very infrequently) into the
project-specific database so I only need one engine and one dbsession. I'm
now trying to correct this monstrosity by binding the external-specific
classes to the external engine, still using a single session.
Per agronholm's suggestion on IRC, I'm attempting to do this via a base
class for each database in order to avoid having to individually bind each
class to the correct engine. Not quite sure how to proceed, though, because
'binds' isn't accepting my keys when those keys are empty base classes.
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import (
scoped_session,
sessionmaker
)
from zope.sqlalchemy import ZopeTransactionExtension
Base = declarative_base()
DBSession =
scoped_session(sessionmaker(extension=ZopeTransactionExtension()))
class DB1(Base):
__abstract__ = True
class DB2(Base):
__abstract__ = True
class SomeInternalClass(DB1):
__tablename__ = 'table_in_db1'
class SomeExternalClass(DB2):
__tablename__ = 'table_in_db2'
db1_engine = engine_from_config(settings, 'sqlalchemy.db1.')
db2_engine = engine_from_config(settings, 'sqlalchemy.db2.')
DBSession.configure(binds={DB1:db1_engine, DB2:db2_engine})
This raises an exception: sqlalchemy.exc.NoInspectionAvailable: No
inspection system is available for object of type <class
'sqlalchemy.ext.declarative.api.DeclarativeMeta'>
But when I keep the same class structure and switch back to the original
bind, it works:
DBSession.configure(bind=db1_engine)
Of course, that means I'm back to using the monster database again. So
what's wrong this?
DBSession.configure(binds={DB1:db1_engine, DB2:db2_engine})
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