Polymorphic tables cause ValueError: can't find value for column parent.name in the results returned about sqlakeyset

[mekhami]

To clarify, it seems to happen when using Joined Table Inheritance

[chenghlee]

To clarify, this is the inheritance pattern that triggers the error:

from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Parent(Base):
    id_ = Column(Integer, primary_key=True)
    cls = Column(Integer, nullable=False, default=0)
    name = Column(String)

    __tablename__ = 'parent'
    __mapper_args__ = {
        'polymorphic_on': cls,
        'polymorphic_identity': 0
    }


class ChildA(Parent):
    child_a_id = Column(Integer, ForeignKey('parent.id_'), primary_key=True)

    __tablename__ = 'child_a'
    __mapper_args__ = {'polymorphic_identity': 1}


class ChildB(Parent):
    child_b_id = Column(Integer, ForeignKey('parent.id_'), primary_key=True)

    __tablename__ = 'child_b'
    __mapper_args__ = {'polymorphic_identity': 2}

The problem seems to come from paging.py, line 74

if entity.__tablename__ == ocol.table_name:

For the joined table inheritance pattern, entity.__tablename__ is not equal to ocol.table_name if ocol comes from the parent table. If you replace that if with something like:

if hasattr(thing, ocol.name):

this bug disappears. But strong warning, I'm not 100% where using hasattr would break any or everything else in the package.

[djrobstep]

Hi, thank you to both of you for reporting this issue!

@chenghlee your suggested change and rationale seems reasonable and I'm happy to make this change (provided the existing tests still pass of course). Do either of you feel like putting together a pull request for this with a simple test case?

Or else I'll fix it up when I get around to it, however that may take a while as I am rather busy at the moment.

[chenghlee]

@djrobstep: I should have some time over the next few days to put together a pull request for this.

[djrobstep]

@chenghlee Super stuff! If you have any questions about the code or whatever just ask.