[sqlalchemy] how to "explicitly" combine columns, for example get the child class value from a query on parent class from same named column?

[Mark Aquino]

I have a polymorphic class structure like this, with a lot of classes 
extending the parent class.  
In reality I'm using a Mixin that declares the visible_id column and it's 
defined with @declared_attr.cascading, but for simplicity:



class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
   visible_id = Column(Integer)

class B(A):
    __tablename__ = 'b'
    id = Column(Integer, ForeignKey("A.id"), primary_key=True)
    visible_id = Column(Integer)


What I need for my application is to query A.visible_id and return the 
CHILD values for B.visible_id (and all the others).

The inheritance works fine, i.e. if i query all As in the database, my 
response is a list of [B] objects, but unless I directly query B the 
visible_id from A takes precedence and I cannot query A.visible_id if I 
remove it from A.

Can anyone tell me how to configure this? 

Thanks!

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