On Sep 22, 11:37 pm, Michael Bayer <mike...@zzzcomputing.com> wrote: > On Sep 22, 2010, at 4:30 AM, Yap Sok Ann wrote: > > > > > This is related to topic "need 0.6_beta2-compat declarative meta" > >http://groups.google.com/group/sqlalchemy/browse_thread/thread/ae7cb9... > > > Prior to version 0.6, I use the following code to automatically add a > > primary key if the table doesn't have one defined: > > > from sqlalchemy.ext.declarative import declarative_base, > > DeclarativeMeta > > from sqlalchemy.schema import Column > > from sqlalchemy.types import Integer > > > class Meta(DeclarativeMeta): > > def __init__(cls, classname, bases, dict_): > > for attr in dict_.itervalues(): > > if isinstance(attr, Column) and attr.primary_key: > > break > > else: > > dict_['id'] = Column(Integer, primary_key=True) > > return super(Meta, cls).__init__(classname, bases, dict_) > > > Base = declarative_base(metaclass=Meta) > > > Of course, that doesn't work anymore in 0.6. The suggestion from the > > aforementioned threads is to replace: > > > dict_['id'] = Column(Integer, primary_key=True) > > > with > > > cls.id = Column(Integer, primary_key=True) > > > Unfortunately, that alone doesn't work in this case. The problem is > > that the Base class itself will be the first one to go through the > > Meta.__init__() method, so the whole thing essentially becomes: > > > Base.id = Column(Integer, primary_key=True) > > > For it to work, I have to wrap the code in an if-block, i.e. > > > class Meta(DeclarativeMeta): > > def __init__(cls, classname, bases, dict_): > > if classname != 'Base': > > for attr in dict_.itervalues(): > > if isinstance(attr, Column) and attr.primary_key: > > break > > else: > > cls.id = Column(Integer, primary_key=True) > > return super(Meta, cls).__init__(classname, bases, dict_) > > > which looks rather ugly. Is there a cleaner way to achieve this? > > I didn't think metaclasses were supposed to be pretty ? Checking that > you're not "the base" is pretty standard metaclass stuff. If the > hardcoded name is the issue, you can look in bases: > > if object not in bases: > > or something more generic: > > for k in cls.__mro__[1:]: > if isinstance(k, Meta): > # you're a Base subclass > Good point. I shall stick with the name checking solution then. Thank you for your help.
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