Whenever I try to establish an adjacency list relationship within a
child class (Department --> Parent Department in this case) the orm
complains about foreign key columns present in both the parent and
child class, and won’t construct the mapping. Below is an example
illustrating the problem. I'd appreciate any insight.
Thanks,
Michael Naber
from sqlalchemy.orm import scoped_session, sessionmaker, relationship,
backref
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine, Column, Integer, String,
ForeignKey, Text, Date
Session = scoped_session(sessionmaker())
Base = declarative_base()
engine = create_engine('sqlite:///data.db')
Session.configure(bind=engine)
class Node(Base):
__tablename__ = 'node'
id = Column(Integer, primary_key=True)
name = Column(String(100))
discriminator = Column('discriminator', String(50))
class Department(Node):
__tablename__ = 'department'
__mapper_args__ = {'polymorphic_identity': 'department'}
id = Column(Integer, ForeignKey('node.id'), primary_key=True)
description = Column(Text)
parent_department_id = Column(Integer,
ForeignKey('department.id'))
parent_department = relationship("Department",
primaryjoin="Department.parent_department_id==Department.id",
foreign_keys="Department.parent_department_id",
backref=backref("subdepartments"), remote_side="Department.id")
Base.metadata.drop_all(checkfirst=True, bind=Session.bind)
Base.metadata.create_all(bind=Session.bind)
s = Session()
d = Department(name='Great Department', description='some text')
s.add(d)
s.commit()
for dept in s.query(Department).all():
print dept.id
print dept.name
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