Thanks for your help! I found the solution :) Instead of doing
dict_['id'] = Column(...) I just do cls.id = Column(...) and it works. Kudos to the writer of this wiki entry http://www.sqlalchemy.org/trac/wiki/UsageRecipes/AutoSequenceGeneration . The comments in there led me to the solution finally. -Matthias On 27 Jul., 15:38, Michael Bayer <mike...@zzzcomputing.com> wrote: > On Jul 27, 2011, at 2:12 AM, Matthias wrote: > > > > > > > Hello, > > > I'm currently writing my own version of the "magic" orm. I'd like it > > to generate id columns automatically. I tried it like shown below. > > > When using the code I get an exception: > > > ArgumentError: Mapper Mapper|Version|version could not assemble any > > primary key columns for mapped table 'Join object on content(55261328) > > and version(64443600)' > > > The problem seems to be in the WithId metaclass. When I put an id = > > Column(... primary = true) by hand on the Version class everything > > works. I was expecting the metaclass to do the same, but apparently > > there must be some difference, > > > Any idea how I can make the Base/Content/Version classes have id > > columns (which work with polymorphism) automatically? I'd like to stay > > away from mixin class all over the place. > > Without looking closely, just the usage of a metaclass is frequently very > difficult. I know that you don't want to use a mixin, but why not specify > your class as part of the declarative base ? > > Base = declarative_base(cls=WithIdBase) > > This question has come up at least twice, maybe three times, in the last few > weeks, so it seems as though the "mixin" section should get an explicit > section about "you can use them as the Base also" - right now its only in the > docstring. > > Another use case that was identified was that of base classes that are not > the "Base", but are in the middle of things. We might add a function to > declarative_base to build such a base, something like mybase = > declarative_base(cls=WithIdBase, derive_from_base=Base). It would be a > small patch. > > > > > -Matthias > > > Code: > > > class WithId(DeclarativeMeta): > > def __init__(cls,classname, bases, dict_): > > if 'id' not in dict_: > > dict_['id'] = Column('id', Integer, > > ForeignKey('content.id'), primary_key=True) > > DeclarativeMeta.__init__(cls, classname, bases, dict_) > > > Base = declarative_base(metaclass=WithId) > > > class Content(db.Base): > > id = db.Column('id', db.Integer, primary_key=True) > > type = db.Column(db.String(250)) > > > @classmethod > > def get_class_name(cls): > > '''Convert CamelCase class name to underscores_between_words > > table name.''' > > name = cls.__name__ > > return ( > > name[0].lower() + > > re.sub(r'([A-Z])', lambda m:"_" + m.group(0).lower(), > > name[1:]) > > ) > > > @db.declared_attr > > def __tablename__(cls): > > return cls.get_class_name() > > > @db.declared_attr > > def __mapper_args__(cls): > > args = { 'polymorphic_identity' : cls.get_class_name() } > > ContentClass = cls.__bases__[-1] > > if ContentClass is db.Base: > > args['polymorphic_on'] = cls.type > > else: > > args['inherit_condition'] = (cls.id == ContentClass.id) > > return args > > > class Version(Content): > > timestamp = Column(DateTime, default=datetime.datetime.now) > > message = Column(UnicodeText) > > #author = attribute(User, backref = > > collectionAttribute('authoredVersions')) > > > -- > > 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 > > athttp://groups.google.com/group/sqlalchemy?hl=en. -- 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.
