Hi Simon, I've got a follow-up question regarding the best practice. You seem to favour binding engine/connection to the Session over to the Metadata, if I understood correctly. However, if my application uses reflection, i.e., autoload=True, that would require that the Table being aware of which database it is referring to. In such circumstance, there seems to be no other choice but binging the engine/connection to Metadata. Do you see any potential problem in my scenario?
And, in this scenario can I safely remove any bindings to the Session, because I can trust the bindings with the Tables? Many thanks! On Wed, Mar 12, 2014 at 3:23 AM, Simon King <si...@simonking.org.uk> wrote: > The order of resolution is described here: > > > http://docs.sqlalchemy.org/en/rel_0_9/orm/session.html#sqlalchemy.orm.session.Session.get_bind > > Binds on the session take priority over binds on metadata (passing an > engine to declarative_base binds the metadata for that base class). > > As far as best practice goes, I would say that it depends on the kind > of program you are writing. Tables (and mapped classes and so on) tend > to be created at module scope. Binding an engine at that point means > that you need to know the database credentials at the time your module > is imported. This is often fine for quick scripts, but can become > annoying when structuring a larger application. For a larger > application, it is probably better to define the structure of your > data model separately from an actual connection to the database. > > Binding at the session level gives you more flexibility, as you can > decide on a per-session basis which engine you want to use (for > example if you had different engines for read and write access). > > Hope that helps, > > Simon > > On Wed, Mar 12, 2014 at 7:25 AM, Bao Niu <niuba...@gmail.com> wrote: > > Ok, let me try rephrasing my question. > > Is binding an engine/connection simultaneously to a Session and a Table > > considered bad practice? I've looked up the documentation but not > > sufficiently confident about this. There seems no definite/official > answer > > to this. Could some experienced users help give a definite clue here? > > Thanks. > > > > > > On Sunday, March 9, 2014 12:08:42 AM UTC-8, Bao Niu wrote: > >> > >> From reading the documentation I learned that you can either bind an > >> engine to a session: > >> >>>engine = create_engine('sqlite:///{}'.format(dbPath), echo=False) > >> >>>Session = sessionmaker(bind=engine) > >> > >> or to a declarative_base: > >> >>>engine = create_engine('sqlite:///{}'.format(dbPath), echo=False) > >> >>>Sqlalchemy_base = declarative_base(engine) > >> > >> Is there a best practice like always binding to a session? > >> I currently bind the engine to both: > >> >>>engine = create_engine('sqlite:///{}'.format(dbPath), echo=False) > >> >>>Session = sessionmaker(bind=engine) > >> >>>Sqlalchemy_base = declarative_base(engine) > >> From running my codes I didn't encounter any problem. But I wonder how > >> SqlAlchemy resolves the conflict internally if there are two bindings? > Is > >> there some potential problems down the road if I kept using this manner? > >> Thanks. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "sqlalchemy" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to sqlalchemy+unsubscr...@googlegroups.com. > > To post to this group, send email to sqlalchemy@googlegroups.com. > > Visit this group at http://groups.google.com/group/sqlalchemy. > > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to a topic in the > Google Groups "sqlalchemy" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/sqlalchemy/QpkScWlfWx8/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > sqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
