hi all,
i have a webapp with an existing database-model ``site``, including users.
in a second service i create a new database-model ``market``, but still
want to access the users (which works via separate engine).
goal: i want to create a relation from the ``market``-model to the
``site``-model. e.g. referencing a ``User`` instance from the
``site``-model to the ``market``-model. like this::
SITE_DATABASE_SCHEMA_NAME = 'site'
MARKET_DATABASE_SCHEMA_NAME = 'market'
def initialize_sql(engine, user_engine = None):
DBSession = scoped_session(sessionmaker(bind=engine))
DBSession.configure(bind=engine)
log.debug('bind market engine')
Base.metadata.bind = engine
# danger: here we try to autogenerate the schema
# Base.metadata.create_all(engine)
if user_engine:
log.debug('bind user engine')
DeclarativeBase.metadata.bind = user_engine
class ProductItem(Base):
"""
cross-db references:
-
http://stackoverflow.com/questions/6433592/cross-database-join-in-sqlalchemy
- http://markmail.org/message/z5tdtlcuoth2osqm
schemas:
http://www.postgresql.org/docs/9.1/static/ddl-schemas.html
"""
__tablename__ = 'product_items'
__table_args__ = {'schema': MARKET_DATABASE_SCHEMA_NAME}
id = sa.Column(sa.BigInteger,
Sequence('place_seq_id', optional=True),
primary_key=True)
name = Column(Unicode(255), unique=True)
user_id = sa.Column(
sa.BigInteger,
sa.ForeignKey('%s.%s.id' % (SITE_DATABASE_SCHEMA_NAME,
User.__tablename__)),
primary_key=True
)
# this one fails
* user = sa.orm.relationship("User")*
question:
- is this possible?
- how can i attach the missing ``User`` class to the known classes for that
sqlalchemy session? now of course i get::
sqlalchemy.exc.InvalidRequestError: When initializing mapper
Mapper|ProductItem|product_items, expression 'User' failed to locate a name
("name 'User' is not defined"). If this is a class name, consider adding
this relationship() to the <class
'if_market.models.ProductItem.ProductItem'> class after both dependent
classes have been defined.
thanks a lot!
best, andi
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