On Mar 29, 2008, at 9:13 AM, Bobby Impollonia wrote:
>
> Hi. I recently switched a sqlalchemy project from using manual mapping
> of classes to ext.declarative.
>
> This is in a turbogears project and I am using their metadata and
> mapper. Before I had:
>
> from turbogears.database import metadata, mapper
> users_table = sqlalchemy.Table('users', metadata, ... )
> class User(object): pass
> mapper(User, users_table)
>
> And now I have:
>
> from turbogears.database import metadata, mapper
> from sqlalchemy.ext.declarative import declarative_base
> Base = declarative_base(metadata=metadata)
> class User(Base):
> __tablename__ = 'users'
> __mapper__ = mapper
ah...we actually had not made the __mapper__ argument settable as of
yet. When using declarative, __mapper__ is readable as the actual
mapper that was created for the class. So here, putting a callable
that generates a mapper is a reasonable idea, though im not sure if
we'd want to put that as "__mapper__" or "__mapper_callable__"....i
like the former but some might say its inconsistent with itself, since
it "changes" from a callable to an actual mapper.
> Any idea how I can get User.query back and have my classes
> automatically associated with my session again? I really like
> declarative and it would be disappointing to have to go back to manual
> mapping of class just for that.
Assuming that TG is using the straight ScopedSession extended mapper,
the most straightforward way here is to use the extension provided by
your configured ScopedSession directly:
class MyClass(base):
__mapper_args__ = {'extension':myscopedsession.extension}
That extension gives you the same behavior that ScopedSession.mapper
does, including the whole "save-on-init" behavior that I'm not
thrilled about. If you only want the "query" property, there is a
newer way to do that which is not as intrusive as
ScopedSession.mapper, which is to use ScopedSession.query_property():
Base = declarative_base(metadata=metadata)
Base.query = myscopedsession.query_property()
that way all classes which extend from Base will have a "query"
attribute available, usable as MyClass.query.filter(...)....
But it still may be convenient to add the functionality you described
earlier, i.e. to just assign the desired mapper callable. Actually
now that im thinking about it it might be more convenient as a kwarg
to declarative_base, like declarative_base(mapper_factory=mapper).
what do you think ?
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