I'm trying to make three `Guy', `Father' and `Father1980' models mapped to
two `guys' and `fathers' tables. Fathers will inherit Guys and Father1980
will inherit Fathers. So I coded it as:
from sqlalchemy import (Table, Binary, Column as C, String, Integer,
ForeignKey, create_engine, MetaData)
from sqlalchemy.orm import (mapper, relationship, backref, scoped_session,
sessionmaker)
metadata = MetaData()
db_engine = create_engine('sqlite:////tmp/test.db', convert_unicode=True)
db_session = scoped_session(sessionmaker(bind=db_engine))
class Guy(object):
pass
class Father(Guy):
def __init__(self, birth):
self.birth = birth
super(Father, self).__init__()
class Father1980(Father):
def __init__(self, *args, **kwargs):
super(Father1980, self).__init__(1980, *args, **kwargs)
guys = Table('guys', metadata,
C('id', Integer, primary_key=True),
C('type', String, nullable=False)
)
fathers = Table('fathers', metadata,
C('id', ForeignKey('guys.id'), primary_key=True),
C('birth', Integer)
)
father80s = Table('fathers_80s', metadata,
C('id', ForeignKey('fathers.id'), primary_key=True),
C('birth', Integer)
)
guysMapper = mapper(Guy, guys, polymorphic_on=guys.c.type)
fathersMapper = mapper(Father, fathers, inherits=guysMapper,
polymorphic_identity='plain-father')
mapper(Father1980, fathers, inherits=fathersMapper,
polymorphic_identity='young-father')
metadata.create_all(bind=db_engine)
f1 = Father(1960)
db_session.add(f1)
f2 = Father1980()
db_session.add(f2)
db_session.commit()
But this will throw cryptic (to me) error:
Traceback (most recent call last):
File "mods.py", line 44, in <module>
polymorphic_identity='young-father')
File "/venv/lib/python2.7/site-packages/sqlalchemy/orm/__init__.py", line
1208, in mapper
return Mapper(class_, local_table, *args, **params)
File "/venv/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
219, in __init__
self._configure_properties()
File "/venv/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
878, in _configure_properties
self._adapt_inherited_property(key, prop, False)
File "/venv/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
1090, in _adapt_inherited_property
self._configure_property(key, prop, init=False, setparent=False)
File "/venv/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line
1117, in _configure_property
prop.columns[0])
File "/venv/lib/python2.7/site-packages/sqlalchemy/sql/expression.py",
line 2737, in corresponding_column
if self.c.contains_column(column):
File "/venv/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
line 612, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "/venv/lib/python2.7/site-packages/sqlalchemy/sql/expression.py",
line 2812, in columns
return self._columns.as_immutable()
AttributeError: 'Table' object has no attribute '_columns'
If I map `Father1980' to table `fathers_80s' instead of table `fathers' the
error will go. I guess mapper didn't see `guys.type' from
`fathersMapper'. Can I make this working?
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