SQLalchemy with nested class

I have a rather complex object that takes a few other objects as its members. Something like this:

from engine import engine

Class Car(objec开发者_运维知识库t):

    def __init__(self,engine_type):
        self.engine=engine(engine_type)

Is there a pain-free approach to map such nested definitions to a database, using SQLAlchemy for example?

Thanks for your help. I am learning SQLAlchemy and working with ORMS.

It's not much clear what you're trying to accomplish. If I understood, you are trying to define Car model with engine attribute that points to another Engine model, and by creating Car object with engine_type, the code should either:

• create Engine object with engine type if it doesn't exist
• load the Engine object with engine type if exists

and then assign it to the Car object.

If so, you should do the following.

class Engine(object):
    def __init__(self, engine_type):
        self.engine_type

    @staticmethod
    def load(engine_type):
        return session.query(Engine)\
                      .filter(engine_type==engine_type).one()

class Car(object):
    def __init__(self, engine_type):
        try:
            engine = Engine.load(engine_type)
        except NoResultsFound:
            engine = Engine(session_type)
            session.add(engine)
        self.engine=engine

You'll need to define to create the 'engine' relationship on the Car mapper yourself, and also you'll need code tweaking to enable scope of the session object where needed.