Hi,
I am trying to implement tables to store a basic multiple inheritance
scheme via SA. I am pretty new to SA and could use some help with the
following code:
<code>
from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.associationproxy import association_proxy
Base = declarative_base()
def _create_inheritance(supertype, subtype):
return Inheritance(supertype, subtype)
class Inheritance(Base):
__tablename__ = 'Inheritance'
sub_name = Column(String(50), ForeignKey('Types.name'),
primary_key=True)
super_name = Column(String(50), ForeignKey('Types.name'),
primary_key=True)
def __init__(self, supertype, subtype):
self.supertype = supertype
self.subtype = subtype
class Types(Base):
__tablename__ = 'Types'
name = Column(String(50), primary_key=True)
abstract = Column(Boolean)
subtypes = association_proxy('Inheritance', 'subtypes', creator =
_create_inheritance)
supertypes = association_proxy('Inheritance', 'supertypes',
creator = _create_inheritance)
def __init__(self, name, abstract = False):
self.name = name
self.abstract = abstract
def __repr__(self):
return "Type(%r)" % (self.name)
class Members(Base):
__tablename__ = 'Members'
name = Column(String(50), primary_key=True)
type_name = Column(String(50),ForeignKey('Types.name'))
type = relationship("Types", backref= "of_members", uselist=False)
of_type_name = Column(String(50),ForeignKey('Types.name'),
primary_key=True)
of_type = relationship("Types", backref='members')
def __init__(self, name, tp):
self.name = name
self.type = tp
def __repr__(self):
return "Member(%r, %r)" % (self.name, type.name)
engine = create_engine('sqlite:///:memory:', echo=False)
Base.metadata.create_all(engine)
if __name__ == "__main__":
Session = sessionmaker(bind=engine)
session = Session()
c1 = Types("A") #<= error below
c2 = Types("B")
c3 = Types("C")
c1.members.append(Members("m1", c2))
</code>
I have the following 2 questions:
1) did i get the relationship between Types and Inheritance right? I
want to be able to call supertypes and subtypes from any type
directly.
2) loose question: how does sqlalchemy handle type errors, e.g. when i
have an A.attr = Column(String), a = A(), a.attr = 15? (i use sqlite
now, which accepts putting string in integer columns, but later i will
use another DB )
3) I get an error for the above code related to the Members class
which i don't understand, can anyone explain/help with a fix:
Traceback (most recent call last):
File "D:\Documents\Code\NetBeans\test\Alchemy\src\alchemy.py", line
60, in <module>
c1 = Types("A")
File "<string>", line 4, in __init__
File "C:\Python27\lib\site-packages\sqlalchemy\orm\state.py", line
100, in initialize_instance
fn(self, instance, args, kwargs)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
2413, in _event_on_init
instrumenting_mapper.compile()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
807, in compile
mapper._post_configure_properties()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
837, in _post_configure_properties
prop.init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\interfaces.py",
line 475, in init
self.do_init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\properties.py",
line 899, in do_init
self._determine_joins()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\properties.py",
line 1028, in _determine_joins
% self)
sqlalchemy.exc.ArgumentError: Could not determine join condition
between parent/child tables on relationship Members.type. Specify a
'primaryjoin' expression. If 'secondary' is present, 'secondaryjoin'
is needed as well.
Any help and clarifications are welcome!
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