RE: [sqlalchemy] Inheriting a functionality in SQLA

[Alexey Vihorev]

Yes, I tried mix-in approach, and it works, thanks.

 

From: sqlalchemy@googlegroups.com [mailto:sqlalchemy@googlegroups.com] On
Behalf Of Robert Forkel
Sent: 20 ноября 2012 г. 17:09
To: sqlalchemy@googlegroups.com
Subject: Re: [sqlalchemy] Inheriting a functionality in SQLA

 

As far as i know each declarative Base has its own metadata registry. You
are using two. Why not use multiple mixins to inherit the columns?

Am 20.11.2012 10:31 schrieb "AlexVhr" <viho...@gmail.com>:

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!

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