Run this:
from sqlalchemy.orm import configure_mappers
configure_mappers()
that ensures RefClass's deferred mapping gets set up appropriately.
On 11/08/2016 01:39 PM, [email protected] wrote:
First, thanks for your very insightful response. I'm trying to reproduce
what you've provided, but I'm getting an `InvalidRequestError` when
querying on `RefClass`:
/InvalidRequestError: SQL expression, column, or mapped entity expected
- got '<class 'RefClass'>'
/
Indeed, RefClass has no `__mapper__` attribute. Querying on any other
object works as intended though. I imagine there's a small detail I'm
missing, so I've highlighted the changes from yesterday's post.
from sqlalchemy import (
Column,
ForeignKey,
Integer,
create_engine,
)
from sqlalchemy.ext.declarative import (
AbstractConcreteBase,
declared_attr,
declarative_base,
has_inherited_table,
)
from sqlalchemy.orm import Session
Base = declarative_base()
class AClass(Base):
__tablename__ = 'aclass'
id = Column(Integer, primary_key=True)
class BClass(Base):
__tablename__ = 'bclass'
id = Column(Integer, primary_key=True)
class RefClass(AbstractConcreteBase, Base):
@declared_attr
def __tablename__(cls):
if cls.__name__ == 'RefClass':
return None
return cls.__name__.lower()
@declared_attr.cascading
def id(cls):
if cls.__name__ == 'RefClass':
return Column(Integer)
column_name = '{}.id'.format(cls.ref.__tablename__)
return Column(ForeignKey(column_name), primary_key=True)
@declared_attr
def __mapper_args__(cls):
if cls.__name__ == 'RefClass':
return {}
return {
'concrete': True,
'polymorphic_identity': cls.ref.__name__
}
class ARefClass(RefClass):
ref = AClass
class BRefClass(RefClass):
ref = BClass
engine = create_engine('sqlite://', echo=True)
Base.metadata.bind = engine
Base.metadata.create_all()
db = Session(engine)
Thanks!
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and
Verifiable Example. See http://stackoverflow.com/help/mcve for a full
description.
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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