Re: [sqlalchemy] relationship supersedes the same relationship on inherited mapper can cause dependency issues during flush

[Mike Bayer]

On 6/18/15 5:04 PM, Kevin Qiu wrote:
Error: SAWarning: Warning: relationship 'staff_obj' on mapper 
'Mapper|ProjectApp|PROJECT_APP' supersedes the same relationship on 
inherited mapper 'Mapper|Application|APPLICATION'; this can cause 
dependency issues during flush
  self._check_conflicts()

Hi !

Thanks for this email.  But I can't do very much with it. First off, I'm 
assuming the "question" here is, "why am I getting this warning?".  The 
only answer to that at the moment would be what the message itself says; 
it means you have another relationship called "staff_obj" on the 
Application class that is conflicting.

We don't see that in your example code, but the example code omits many 
details such as what the "app_category" object is as well as any kind of 
foreign key between Application and ProjectApp, so I can only assume 
that a second "staff_obj" relationship must be in the real code as 
well.   If this is not the case, then you'd need to supply a fully 
working test case - below I've provided one which you can alter to show 
me how it is producing this warning when it shouldn't be.   The example 
includes assumed values of the missing elements added back in, and it 
runs without warnings.

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class Staff(Base):
    __tablename__ = 'STAFF'
    staff_id = Column(String(20), primary_key=True)


class Application(Base):
    __tablename__ = 'APPLICATION'
    app_id = Column(Integer, primary_key=True)

    # I had to add this because it was missing from the example
    app_category = Column(String)

    __mapper_args__ = {
        'polymorphic_identity': 'application',
        'polymorphic_on': app_category
    }


class ProjectApp(Application):
    __tablename__ = 'PROJECT_APP'

    app_id = Column(Integer, primary_key=True)

    # I had to add this since to support joined table inheritance
    # there needs to be a foreign key relationship
    super_app_id = Column(Integer, ForeignKey('APPLICATION.app_id'))

    # I had to comment this out because there is no C_SUPERVISOR
    # mapping here
    # c_supervisor = Column(String(62), 
ForeignKey('C_SUPERVISOR.c_sup_email'))

    u_supervisor = Column(String(20), ForeignKey('STAFF.staff_id'))
    staff_obj = relationship('Staff', backref='projectapp_objs')
    __mapper_args__ = {
        'polymorphic_identity': 'projApp',
    }

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

s = Session(e)
p1, p2, p3 = ProjectApp(), ProjectApp(), ProjectApp()

s.add_all([
    Staff(staff_id='s1', projectapp_objs=[p1, p2]),
    Staff(staff_id='s2', projectapp_objs=[p3]),
])
s.commit()

assert p2.staff_obj.staff_id == 's1'

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