On Nov 20, 2012, at 4:31 AM, AlexVhr wrote:
> I'm trying to incapsulate some functionality (some columns mainly) into base
> classes to inherit my models from them. The setup looks like this:
>
> class EntityTemplate():
> @declared_attr
> def __tablename__(cls):
> return cls.__name__.lower()
> id = Column(Integer(), primary_key=True)
> timestamp = Column(DateTime())
>
> class DocumentTemplate(EntityTemplate):
> date = Column(Date())
> number = Column(String(5))
>
> Entity = declarative_base(cls=EntityTemplate, name='Entity')
> Document = declarative_base(cls=DocumentTemplate, name='Document')
> I'm trying to use it like this:
>
> class Customer(Entity):
> name = Column(String(25))
> address = Column(String(50))
>
> class Invoice(Document):
> customer_id = Column(Integer, ForeignKey('customer.id'))
> customer = relationship("Customer")
> total = Column(Numeric(10,2))
>
> Entity.metadata.create_all(engine)
> Document.metadata.create_all(engine)
> But on the last line I get this:
>
> sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column
> 'invoice.customer_id' could not find table 'customer' with which to generate
> a foreign key to target column 'id'
> If I inherit Invoice from Entity instead of Document, everything is fine
> (except the fact that columns date and number are missing). Why? (I'm using
> SQLAlchemy-0.7.9-py3.2). Thanks!
>
>
the use of two different declarative_base() makes this more complicated as
there is no common MetaData collection between the two classes which allows
foreign keys to be resolve based on string names, as well as class names like
"Customer" to be resolved. the Base + MetaData combination represent a pair of
registries that allow these string lookups to work.
So using one declarative base would solve the issue, else you need to forego
the usage of string identifiers and pass object references instead:
customer_id = Column(Integer, ForeignKey(Customer.id))
customer = relationship(Customer)
but there's really no need to use two different declarative bases, your
EntityTemplate and DocumentTemplate are mixins, which if you'd like them to be
packed into a single base class can be accomplished using a subclass of a
single Base with the __abstract__ = True flag.
http://docs.sqlalchemy.org/en/rel_0_8/orm/extensions/declarative.html#abstract
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalchemy@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
