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.
-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'))
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