Great, and to answer your TODO no, metadata.bind = engine is not necessary and
I try to discourage people from using that activity by default (but the
plethora of Turbogears and Pylons tutorials that keep using it makes this task
more or less impossible). A discussion of that feature specifically is at
http://www.sqlalchemy.org/docs/core/schema.html#binding-metadata-to-an-engine-or-connection
.
On Aug 17, 2011, at 12:03 PM, Tim Black wrote:
> Michael,
>
> Thank you for your advice. It took me a while to figure out how to follow
> it, but in the end it worked. After reading the (excellent) SQLAlchemy docs
> a lot more, and some other discussion group posts that explained the function
> of the engine, metadata, and session objects, and reassured me it was
> possible to have two databases, two engines, one metadata, and one session, I
> figured out how to modify the TurboGears 2.1 multiple database setup (linked
> below) to work that way. For others' reference, the essential modifications
> to TurboGears' multiple databases setup (not including the necessary changes
> to imports in model sub-modules) for making a relation between two databases
> are below.
>
> Tim
>
> --- /tmp/bzr-diff-EWNNdM/old/projects/projects/model/__init__.py
> +++ /tmp/bzr-diff-EWNNdM/new/projects/projects/model/__init__.py
> @@ -12,16 +12,16 @@
>
> -maker2 = sessionmaker(autoflush=True, autocommit=False,
> - extension=ZopeTransactionExtension())
> -DBSession2 = scoped_session(maker2)
> +#maker2 = sessionmaker(autoflush=True, autocommit=False,
> +# extension=ZopeTransactionExtension())
> +#DBSession2 = scoped_session(maker2)
>
> -DeclarativeBase2 = declarative_base()
> +#DeclarativeBase2 = declarative_base()
>
> @@ -35,11 +35,11 @@
>
> -metadata2 = DeclarativeBase2.metadata
> +#metadata2 = DeclarativeBase2.metadata
>
> @@ -49,10 +49,12 @@
>
> def init_model(engine1, engine2):
> """Call me before using any of the tables or classes in the model."""
>
> # DBSession.configure(bind=engine)
> DBSession.configure(bind=engine1)
> - DBSession2.configure(bind=engine2)
> + DBSession.configure(binds={Ticket:engine2})
> + #DBSession2.configure(bind=engine2)
>
> + # TODO: Is this statement necessary, since the engines are already
> configured in the session?
> metadata.bind = engine1
> - metadata2.bind = engine2
> + #metadata2.bind = engine2
>
> On 08/13/2011 05:43 PM, Michael Bayer wrote:
>>
>> Do you have the "metadata" in Table shared with the metadata used by
>> DeclarativeBase ? Otherwise the name "ticket" won't be located via the
>> ForeignKey you're declaring in the WorkDone class. As an alternative you
>> could link the ForeignKey to "ticket.c.id" but would be easier if you could
>> use the "DeclarativeBase.metadata" for all table definitions.
>>
>> Otherwise yes you need to ensure that trac.py and main.py have both been
>> imported before you attempt to use the mappings.
>>
>>
>> On Aug 13, 2011, at 4:01 PM, Tim Black wrote:
>>
>>> I'm getting the following error message running TurboGears 2.1.1 and
>>> SQLAlchemy 0.7.2, using TurboGears' multiple database setup described here:
>>> http://turbogears.org/2.1/docs/main/MultipleDatabases.html.
>>> Both databases are SQLite3 databases; one is the main database for the
>>> TurboGears app; the other is a Trac 0.11.4 database. Can you help me
>>> figure out what I'm doing wrong?
>>>
>>> InvalidRequestError: One or more mappers failed to initialize - can't
>>> proceed with initialization of other mappers. Original exception was: When
>>> initializing mapper Mapper|WorkDone|work_done, expression 'ticket' failed
>>> to locate a name ("name 'ticket' is not defined"). If this is a class name,
>>> consider adding this relationship() to the <class
>>> 'projects.model.main.WorkDone'> class after both dependent classes have
>>> been defined.
>>>
>>> In my model/__init__.py, I import the model objects in this order (the
>>> traceback makes me think this is the right place to work--either I need to
>>> change the import order here, or add the relation() after the final import,
>>> but neither of these solutions have seemed to work):
>>>
>>> from projects.model.trac import ticket
>>> from projects.model.main import WorkDone
>>> # To follow the error message's instructions, I tried adding a relation()
>>> here, but it generated a further error; maybe I didn't get the syntax right.
>>>
>>> If I should add a relation immediately above, what is the right syntax?
>>> But this also seems like a hack to add a relation() here; if I have to add
>>> a relation() here, does that mean my current code has circular dependencies?
>>>
>>> Here's the rest of my relevant code (with important items in bold):
>>>
>>> In projects/model/trac.py, I have the following (I haven't put any
>>> relation() or backref in this table definition, because this file is
>>> borrowed mostly unmodified from Trac's experimental SQLAlchemy model object
>>> code, and I want to keep it that way):
>>>
>>> # begin Tim's modification
>>> from projects.model import metadata2
>>> metadata = metadata2
>>> # end Tim's modification
>>>
>>> # Ticket system
>>> ticket = Table('ticket', metadata,
>>> Column('id', Integer, primary_key=True),
>>> Column('type', Text),
>>> Column('time', Integer, index=True),
>>> Column('changetime', Integer),
>>> Column('component', Text),
>>> Column('severity', Text),
>>> Column('priority', Text),
>>> Column('owner', Text),
>>> Column('reporter', Text),
>>> Column('cc', Text),
>>> Column('version', Text),
>>> Column('milestone', Text),
>>> Column('status', Text, index=True),
>>> Column('resolution', Text),
>>> Column('summary', Text),
>>> Column('description', Text),
>>> Column('keywords', Text))
>>>
>>> In projects/model/main.py, I have:
>>>
>>> class WorkDone(DeclarativeBase):
>>> __tablename__ = 'work_done'
>>> id = Column(Integer, primary_key=True)
>>> ticket_id = Column('ticket_id', Integer, ForeignKey('ticket.id')) #
>>> many-to-one
>>> ticket = relation('ticket', primaryjoin=ticket_id == 'ticket.id')
>>>
>>> The traceback is generated by line 105 of my projects/controllers/root.py,
>>> which reads:
>>>
>>> for p in DBSession.query(model.Project):
>>>
>>> projects/model/main.py contains:
>>>
>>> class Project(DeclarativeBase):
>>> id = Column(Integer, primary_key=True)
>>> workDone = relation('WorkDone') # one-to-many
>>>
>>> ...and that same class contains several properties that reference the
>>> WorkDone model object like this one does:
>>>
>>> @property
>>> def totalHours(self):
>>> return sum([w.elapsed for w in self.workDone])
>>>
>>> Thank you for any help you can offer!
>>>
>>> Tim
>>>
>>>
>
>
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