Retrieving SQLAlchemy query objects through declaritive_base class methods

Question

I can't help but think that the number of keystrokes required to do a query in SQLAlchemy is a little on the high side.

DBSession.query(User).filter(...).first()

Is there anything wrong with doing something like this?

DBSession = scoped_session(sessionmaker())

class BaseWithDBSession(object):
    def delete(self):
        DBSession.delete(self)

    @classmethod
    def query(cls):
        return DBSession.query(cls)


Base = declarative_base(cls=BaseWithDBSession)

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    ...

user = User.query().filter(User.id==1).one()
user.delete()

This approach seems a lot neater to me, and it also means I don't have to import DBSession between code files. The downside is that all of my classes are tied to a particular session, but I can't think of any situation in which I would want anything different. I'm trying to think of reasons why I haven't seen this approach before (apart from my inexperience)...

Vinay Sajip · Accepted Answer · 2011-07-14 13:23:55Z

2

Well, there are many ways of doing this sort of thing - see Mike Bayer's tongue-in-cheek post about Magic, a "new" ORM. SQLAlchemy postions itself as a toolkit rather than a framework, so that it can be used in different ways according to the needs of different scenarios. For example, there will be scenarios when a single session is not enough.

There are also third-party declarative layers on top of SQLAlchemy - e.g. Elixir. It offers a slightly different way of doing things.

answered Jul 14, 2011 at 13:23

Vinay Sajip

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1 Comment

mattjbray Over a year ago

Mike Bayer's quote, "SQLAlchemy isn't a framework ... it's a toolkit", seems to sum up my conceptual issues, and Elixir does exactly what I specified above. Thanks.

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