You could inject the attributes in a metaclass:
def common_columns():
return dict(id = Column(Integer, primary_key=True),
foo = Column(String))
Base = None
class mymeta(DeclarativeMeta):
def __init__(self, name, bases, attrs):
if Base is not None:
# a real sub class
attrs.update(common_columns())
DeclarativeMeta.__init__(self, name, bases, attrs)
Base = declarative_base(metaclass=mymeta)
But note that the declarative system has a counter so the column
definitions are ordered correctly for create statements. I don't know
if this would adversely affect that.
On Dec 17, 9:30 pm, Chris Withers <ch...@simplistix.co.uk> wrote:
> Hi All,
>
> So, say you have some common methods and field definitions that you want
> to share across a bunch of mapper classes. My python head says that
> these should all go in a base class, say, for example:
>
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.schema import Column
> from sqlalchemy.types import Integer, String, DateTime
>
> Base = declarative_base()
>
> class TheBase(Base):
>
> id = Column(Integer, primary_key=True)
> ref = Column(Integer, nullable=False, index=True)
> valid_from = Column(DateTime(), nullable=False, index=True)
> valid_to = Column(DateTime(), index=True)
> entered_by = Column(String(255), nullable=False, index=True)
> deleted_by = Column(String(255), index=True)
>
> def some_func(self, x,y):
> ...
>
> But, this results in:
>
> sqlalchemy.exc.InvalidRequestError: Class <class 'TheBase'> does not
> have a __table__ or __tablename__ specified and does not inherit from an
> existing table-mapped class.
>
> How should I create a class like this? This isn't about table
> inheritance or the like and I'm *sure* I was told an easy solution for
> this specific use case before, but I can't find it for the life of me now...
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
> -http://www.simplistix.co.uk
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