Calling configure_mappers() fixes the  issue. 

However, the next thing I tried was to do joined load ( for eager loading ) 
, and it fails. 

This is what I tried : 


order = db.session.query(Order).join(Order.items.of_type(order_items)).
options(joinedload(Order.items.of_type(order_items))).all() 




This returns an error: 

InvalidRequestError: Detected unaliased columns when generating joined load.  
Make sure to use aliased=True or flat=True when using joined loading with 
with_polymorphic().



So I added aliased= True in my polymorphic union, and when i query, i the same 
error: 


InvalidRequestError: Detected unaliased columns when generating joined load.  
Make sure to use aliased=True or flat=True when using joined loading with 
with_polymorphic().




On Wednesday, 7 March 2018 16:05:49 UTC-5, Mike Bayer wrote:
>
> my test doesn't have that problem, try calling configure_mappers() 
> first.   Try running the test case I have as given. 
>
> On Wed, Mar 7, 2018 at 4:02 PM, Harshvardhan Gupta 
> <harsh...@gmail.com <javascript:>> wrote: 
> > Thanks for the reply. 
> > 
> > Sorry, I will be more careful when i sent code snippets. 
> > 
> > I tried this out after you asked me to remove flat =True, so the code 
> looks 
> > like this now : 
> > 
> > 
> > pjoin = polymorphic_union({ 
> >     'order_test_item': OrderTestItem.__table__, 
> > }, 'type', 'pjoin')   # I dont think 'type' should exist. 
> > 
> > 
> > order_items = with_polymorphic( 
> >     OrderItem, [OrderTestItem], selectable=pjoin) 
> > 
> > 
> > Now i get a different Error : 
> > 
> > 
> --------------------------------------------------------------------------- 
> > UnmappedClassError                        Traceback (most recent call 
> last) 
> > <ipython-input-10-d281fb038587> in <module>() 
> >       4 
> >       5 order_items = with_polymorphic( 
> > ----> 6     OrderItem, [OrderTestItem], selectable=pjoin) 
> > 
> > 
> ~/.virtualenvs/app-flask-rest-backend-36/lib/python3.6/site-packages/sqlalchemy/orm/util.py
>  
>
> > in with_polymorphic(base, classes, selectable, flat, polymorphic_on, 
> > aliased, innerjoin, _use_mapper_path, _existing_alias) 
> >     771        only be specified if querying for one specific subtype 
> only 
> >     772     """ 
> > --> 773     primary_mapper = _class_to_mapper(base) 
> >     774     if _existing_alias: 
> >     775         assert _existing_alias.mapper is primary_mapper 
> > 
> > 
> ~/.virtualenvs/app-flask-rest-backend-36/lib/python3.6/site-packages/sqlalchemy/orm/base.py
>  
>
> > in _class_to_mapper(class_or_mapper) 
> >     308         return insp.mapper 
> >     309     else: 
> > --> 310         raise exc.UnmappedClassError(class_or_mapper) 
> >     311 
> >     312 
> > 
> > UnmappedClassError: Class 'models.Item.OrderItem' is not mapped 
> > 
> > 
> > My models are defined as my original post, like this : 
> > 
> > 
> > class OrderItem(Dictifiable, AbstractConcreteBase, db.Model): 
> >  pass 
> > 
> > 
> > class OrderTestItem(OrderItem): 
> >  order_id = Column(Integer, ForeignKey("order.id"), primary_key=True) 
> >  test_id = Column(Integer, ForeignKey("test.id"), primary_key=True) 
> > 
> >  test = relationship('Test') 
> >  order = relationship('Order') 
> > 
> >  __mapper_args__ = { 
> >  'polymorphic_identity': 'order_test_item', 
> >  'concrete': True, 
> >  } 
> > 
> > 
> > class Order(Dictifiable, db.Model): 
> >     id = Column(Integer, Sequence('user_id_seq'), primary_key=True) 
> >     rp_id = Column(Integer, nullable=False) 
> > 
> >     user_id = Column(Integer, ForeignKey('user.id')) 
> > 
> >     user = relationship('User') 
> >     items = relationship('OrderItem') 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > On Wednesday, 7 March 2018 15:48:58 UTC-5, Mike Bayer wrote: 
> >> 
> >> here's a full MCVE, which with "flat=True" reproduces your issue 
> >> exactly (send me this next time).   The issue is the "flat=True", take 
> >> that out because it isn't compatible with a concrete union - it 
> >> implies the "aliased" flag and that gets in the way of what the 
> >> polymorphic_union() function is doing already. 
> >> 
> >> 
> >> from sqlalchemy import * 
> >> from sqlalchemy.orm import * 
> >> from sqlalchemy.ext.declarative import declarative_base 
> >> from sqlalchemy.ext.declarative import declared_attr 
> >> from sqlalchemy.ext.declarative import AbstractConcreteBase 
> >> 
> >> Base = declarative_base() 
> >> 
> >> 
> >> class OrderItem(AbstractConcreteBase, Base): 
> >>     pass 
> >> 
> >> 
> >> class OrderTestItem(OrderItem): 
> >>     __tablename__ = 'order_test_item' 
> >> 
> >>     order_id = Column(Integer, ForeignKey("order.id"), 
> primary_key=True) 
> >>     test_id = Column(Integer, ForeignKey("test.id"), primary_key=True) 
> >> 
> >>     test = relationship('Test') 
> >>     order = relationship('Order') 
> >> 
> >>     __mapper_args__ = { 
> >>         'polymorphic_identity': 'order_test_item', 
> >>         'concrete': True 
> >>     } 
> >> 
> >> 
> >> class User(Base): 
> >>     __tablename__ = 'user' 
> >>     id = Column(Integer, primary_key=True) 
> >> 
> >> 
> >> class Test(Base): 
> >>     __tablename__ = 'test' 
> >>     id = Column(Integer, primary_key=True) 
> >> 
> >> 
> >> class Order(Base): 
> >>     __tablename__ = 'order' 
> >> 
> >>     id = Column(Integer, primary_key=True) 
> >> 
> >>     user_id = Column(Integer, ForeignKey('user.id')) 
> >> 
> >>     user = relationship('User') 
> >>     items = relationship('OrderItem') 
> >> 
> >> e = create_engine("sqlite://", echo=True) 
> >> Base.metadata.create_all(e) 
> >> 
> >> s = Session(e) 
> >> 
> >> t1, t2 = Test(), Test() 
> >> s.add(Order(items=[OrderTestItem(test=t1), OrderTestItem(test=t2)])) 
> >> s.commit() 
> >> 
> >> 
> >> pjoin = polymorphic_union({ 
> >>     'order_test_item': OrderTestItem.__table__, 
> >> }, 'type', 'pjoin') 
> >> 
> >> order_items = with_polymorphic( 
> >>     OrderItem, [OrderTestItem], selectable=pjoin) 
> >> 
> >> 
> >> s = Session(e) 
> >> order = s.query(Order).join(Order.items.of_type(order_items)).all() 
> >> 
> >> 
> >> 
> >> 
> >> On Wed, Mar 7, 2018 at 3:36 PM, Harshvardhan Gupta 
> >> <harsh...@gmail.com> wrote: 
> >> > Thanks for replying. 
> >> > I forgot to show the error. 
> >> > It is this: 
> >> > 
> >> > 1054, "Unknown column 'pjoin.order_id' in 'on clause'") [SQL: "SELECT 
> >> > `order`.id AS order_id, `order`.rp_id AS order_rp_id, `order`.user_id 
> AS 
> >> > order_user_id \nFROM `order` INNER JOIN (SELECT 
> order_test_item.order_id 
> >> > AS 
> >> > order_id, order_test_item.test_id AS test_id, 'order_test_item' AS 
> type 
> >> > \nFROM order_test_item) AS anon_1 ON `order`.id = pjoin.order_id" 
> >> > 
> >> > 
> >> > 
> >> > 
> >> > On Wednesday, 7 March 2018 15:28:54 UTC-5, Mike Bayer wrote: 
> >> >> 
> >> >> On Tue, Mar 6, 2018 at 8:36 PM, Harshvardhan Gupta 
> >> >> <harsh...@gmail.com> wrote: 
> >> >> > I tried to use AbstractConcreteBase for polymorphic relationships 
> , 
> >> >> > but 
> >> >> > I am 
> >> >> > getting errors. The examples in sqlalchemy cover normal 
> polymorphism 
> >> >> > well, 
> >> >> > but not those with Abstract Base classes. 
> >> >> > 
> >> >> > 
> >> >> > I have already asked a question on stack overflow . 
> >> >> > 
> >> >> > The gist of the question is: 
> >> >> > 
> >> >> > class OrderItem(Dictifiable, AbstractConcreteBase, db.Model): 
> >> >> >     pass 
> >> >> > 
> >> >> > 
> >> >> > class OrderTestItem(OrderItem): 
> >> >> >     order_id = Column(Integer, ForeignKey("order.id"), 
> >> >> > primary_key=True) 
> >> >> >     test_id = Column(Integer, ForeignKey("test.id"), 
> >> >> > primary_key=True) 
> >> >> > 
> >> >> >     test = relationship('Test') 
> >> >> >     order = relationship('Order') 
> >> >> > 
> >> >> >     __mapper_args__ = { 
> >> >> >         'polymorphic_identity': 'order_test_item', 
> >> >> >         'concrete': True 
> >> >> >     } 
> >> >> > 
> >> >> > 
> >> >> > 
> >> >> > class Order(Dictifiable, db.Model): # This class has a relation to 
> >> >> > the 
> >> >> > polymorphic class 
> >> >> > 
> >> >> >     id = Column(Integer, Sequence('user_id_seq'), 
> primary_key=True) 
> >> >> > 
> >> >> >     user_id = Column(Integer, ForeignKey('user.id')) 
> >> >> > 
> >> >> >     user = relationship('User') 
> >> >> >     items = relationship('OrderItem') 
> >> >> > 
> >> >> > 
> >> >> > I query like : 
> >> >> > 
> >> >> > pjoin = polymorphic_union({ 
> >> >> >     'order_test_item': OrderTestItem.__table__, 
> >> >> > }, 'type', 'pjoin') 
> >> >> > 
> >> >> > order_items = 
> >> >> > 
> >> >> > 
> with_polymorphic(OrderItem,[OrderTestItem],selectable=pjoin,flat=True) 
> >> >> > 
> >> >> > And my actual query : 
> >> >> > 
> >> >> > order = Order.query.join(Order.items.of_type(order_items)).all() 
> >> >> > 
> >> >> > 
> >> >> > I would like to know what the correct way to query these tables 
> is, 
> >> >> > how 
> >> >> > to 
> >> >> > eager load polymorphic tables, and how to filter on the 
> >> >> > relationships. 
> >> >> 
> >> >> looks correct to me.  what is "the error" ?   can you provide full 
> >> >> MCVE + complete stack trace? 
> >> >> 
> >> >> 
> >> >> 
> >> >> > 
> >> >> > I plan to send a pull request with an example of these test cases 
> >> >> > after 
> >> >> > I 
> >> >> > know the answers myself. 
> >> >> > 
> >> >> > 
> >> >> > -- 
> >> >> > 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. 
> >> >> > --- 
> >> >> > You received this message because you are subscribed to the Google 
> >> >> > Groups 
> >> >> > "sqlalchemy" group. 
> >> >> > To unsubscribe from this group and stop receiving emails from it, 
> >> >> > send 
> >> >> > an 
> >> >> > email to sqlalchemy+...@googlegroups.com. 
> >> >> > To post to this group, send email to sqlal...@googlegroups.com. 
> >> >> > Visit this group at https://groups.google.com/group/sqlalchemy. 
> >> >> > For more options, visit https://groups.google.com/d/optout. 
> >> > 
> >> > -- 
> >> > 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. 
> >> > --- 
> >> > You received this message because you are subscribed to the Google 
> >> > Groups 
> >> > "sqlalchemy" group. 
> >> > To unsubscribe from this group and stop receiving emails from it, 
> send 
> >> > an 
> >> > email to sqlalchemy+...@googlegroups.com. 
> >> > To post to this group, send email to sqlal...@googlegroups.com. 
> >> > Visit this group at https://groups.google.com/group/sqlalchemy. 
> >> > For more options, visit https://groups.google.com/d/optout. 
> > 
> > -- 
> > 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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> > email to sqlalchemy+...@googlegroups.com <javascript:>. 
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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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