Hi all,
I tried to convert some existing code containing an adjacency list to
mix-ins, and the mix-in version doesn't seem to be liked by SQLAlchemy
0.6_beta1:
Original code that works:
class ClassDefaults(DeclarativeMeta):
def __init__(cls,classname, bases, dict_):
dict_['id'] = Column(Integer, Sequence("id_seq",
optional=True), primary_key=True)
return DeclarativeMeta.__init__(cls, classname, bases, dict_)
Base = declarative_base(metaclass=ClassDefaults)
class Location(Base):
__tablename__ = 'location'
parent_id = Column(Integer, ForeignKey('location.id'))
parent = relation('Location', backref=backref('children'),
remote_side='location.c.id')
name = UniqueString(25)
desc = Column(String(80))
New Mix-In code that doesn't work:
Base = declarative_base()
class Common(object):
id = Column(Integer, Sequence('id_seq', optional=True),
primary_key=True)
class Location(Base,Common):
__tablename__ = 'location'
parent_id = Column(Integer, ForeignKey('location.id'))
parent = relation('Location', backref=backref('children'),
remote_side='location.c.id')
name = UniqueString(25)
desc = Column(String(80))
SQLAlchemy complains:
Traceback (most recent call last):
File "base.py", line 60, in <module>
class Location(Base,Common):
File "/usr/lib64/python2.6/site-packages/sqlalchemy/ext/declarative.py",
line 561, in __init__
_as_declarative(cls, classname, dict_)
File "/usr/lib64/python2.6/site-packages/sqlalchemy/ext/declarative.py",
line 554, in _as_declarative
cls.__mapper__ = mapper_cls(cls, table, properties=our_stuff, **mapper_args)
File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/__init__.py",
line 778, in mapper
return Mapper(class_, local_table, *args, **params)
File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/mapper.py",
line 189, in __init__
self._configure_pks()
File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/mapper.py",
line 435, in _configure_pks
"key columns for mapped table '%s'" % (self, self.mapped_table.description))
sqlalchemy.exc.ArgumentError: Mapper Mapper|Location|location could
not assemble any primary key columns for mapped table 'location'
Question: do Mix-ins complicate the mechanism by which adjacency lists
are defined? If so, how does one work around this (and maybe update
the Mix-in docs to show an example of how to work around this issue?)
Thanks,
Daniel
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