I'm trying to do something a little unusual, I'm open to alternative ideas
for how to accomplish this as well but I think I need a 3 column mixer
table with 3 foreign keys.
Right now I have many to many relationships between 3 tables, e.g.
a m2m b
b mbm c
however, I really something like (a_id, b_id, c_id) (again, could be a
different way that i'm totally open to using) because only some Bs and Cs
will be valid for an A, and so forth.
i still need to be able to associate many to many with each other, but with
a discriminator (where) on the third column like a.bs where c=some_value
Is an association object capable of this or am I barking up the wrong tree?
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Integer, Column, ForeignKey
from sqlalchemy.orm import relationship
Base = declarative_base()
class Association(Base):
__tablename__ = 'association'
a_id = Column(ForeignKey('a.id'), primary_key=True)
b_id = Column(ForeignKey('b.id'), primary_key=True)
c_id = Column(ForeignKey('c.id'), primary_key=True)
parent = relationship("A", back_populates="children")
child = relationship("B", back_populates="parents")
#cousin = relationship("C", back_populates="relatives") ???
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
children = relationship("Association", back_populates="parent")
class B(Base):
__tablename__ = 'b'
id = Column(Integer, primary_key=True)
parents = relationship("Association", back_populates="child")
class C(Base):
__tablename__ = 'c'
id = Column(Integer, primary_key=True)
# relatives = relationship("Association", back_populates="cousin")
--
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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