On Nov 17, 2008, at 7:17 AM, Power Button wrote:
>
> What I have tried is putting all the setup instructions into a class
> and instantiating this in myApp.py. This doesn't make it global to all
> the modules though. Do I need to pass this object around to all
> classes as arguments to __init__() in order to reference this class?
> (this seems a bit bulky to me)
Neither your classes, mappers, or Table objects need any knowledge of
the Session or engine in order to be defined. Table objects only need
a MetaData() object, which you probably want to define once in a
single module, which is imported by all of your other modules. If
using declarative, then your declarative base class takes the place of
the MetaData object.
The Session and engine should also be instantiated once globally.
When you start using the Session against particular classes, that's
when they have some association with the database.
> Here is my Bootstrap class
>
> class Bootstrap(object):
> def __init__(self):
> self.mDb = MyDb() #my DB abstraction class
> self.mEngine = self.mDb.getEngine()
> self.mSession = self.mDb.getSession()
> self.mMeta = self.mDb.getMeta(self.mEngine)
>
> if self.mTable1 == None:
> self. mTable1 = self.mDb.getTable("table1", self.mMeta)
> self.mEdoMapper = mapper(Table1, self. mTable1)
>
> if self.mTable2 == None:
> self. mTable2 = self.mDb.getTable("table2", self.mMeta)
> self.mEdoMapper = mapper(Table2, self. mTable2)
this is overly complex. You dont need any reference to mapper
objects, and the Table objects don't need to be so formally assigned
either. A simple setup looks like:
base.py
----------
# global MetaData object
metadata = MetaData()
model1.py
--------------
import base
class MyClass(object):
.....
t1 = Table('sometable', base.metadata, ...)
mapper(MyClass, t1)
# more classes and tables
model2.py
--------------
import base
class SomeOtherClass(object):
.....
t1 = Table('....', ....)
mapper(SomeOtherClass, t2, ...)
bootstrap.py
----------------
# configure the database connection/session
import base
engine = create_engine('my engine://')
Session = scoped_session(sessionmaker(bind=engine))
def create_tables():
"""create all tables which don't yet exist in the DB."""
base.metadata.create_all(engine)
application.py
-------------------
from bootstrap import Session
frmo model1 import MyClass
print Session.query(MyClass).all()
I would also recommend the usage of declarative,
http://www.sqlalchemy.org/docs/05/plugins.html#plugins_declarative
, which simply means that the separate class/Table/mapper() objects
are defined at once, and it also allows dependencies between mapped
classes to be defined using strings which can reduce or remove
circular dependency issues.
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