I think what the OP would have to do is write a UNION, that is: s.query(Child1).filter(Child1.thing == "thing").union( s.query(Child2).filter(Child2.thing == "thing") )
that's how this problem is approached in SQL. With SQLAlchemy, any problem should be solved by considering the desired structure in SQL first. On Wed, Feb 3, 2021, at 10:14 AM, Simon King wrote: > I don't think you're going to find a way to do that built in to SQLAlchemy. > > When you write "session.query(Parent)", SQLAlchemy constructs a query > against the "parent" table. But to filter by your "is_done" property, > it would suddenly need to join every child table into the query and > construct a complicated WHERE clause along the lines of "(type_ = > 'child_one' AND child_one.requested_type_one = > child_one.delivered_type_one) OR (type_ = 'child_two' AND > child_two.requested_type_two = child_one.delivered_type_two)". > > In theory, I think you *could* implement this as a hybrid property on > Parent, where the "expression" part of the hybrid property constructs > a subquery with a union or a join of all the child tables. It'll be > pretty messy, and might not perform particularly well. > > Simon > > On Wed, Feb 3, 2021 at 10:08 AM Mehrdad Pedramfar > <[email protected]> wrote: > > > > The structure I have created is like below: > > > > > > class Parent(Base): > > __tablename__ = 'parent' > > > > id = Field( > > Integer, > > primary_key=True > > ) > > > > type_ = Field( > > String(50), > > readonly=True > > ) > > > > __mapper_args__ = { > > 'polymorphic_on': type_, > > } > > > > class ChildOne(Parent): > > __tablename__ = 'child_one' > > __mapper_args__ = { > > 'polymorphic_identity': 'child_one' > > } > > > > id = Field( > > Integer, > > ForeignKey('parent.id'), > > primary_key=True > > ) > > > > requested_type_one = Column( > > Integer, > > nullable=False, > > ) > > delivered_type_one = Column( > > Integer, > > nullable=False, > > ) > > is_done = column_property( > > requested_type_one == delivered_type_one > > ) > > > > class ChildTwo(Parent): > > __tablename__ = 'child_two' > > __mapper_args__ = { > > 'polymorphic_identity': 'child_two' > > } > > > > id = Field( > > Integer, > > ForeignKey('parent.id'), > > primary_key=True > > ) > > > > requested_type_two = Column( > > Integer, > > nullable=False, > > ) > > delivered_type_two = Column( > > Integer, > > nullable=False, > > ) > > is_done = column_property( > > requested_type_two == delivered_type_two > > ) > > > > > > What I am looking for is to execute ORM query like this: > > > > session.query(Parent).filter(Parent.is_done.is_(True)).all() > > > > which raises `Parent class does not have is_done` error. > > > > I want that parent class gets Child class's `is_done` based on different > > types of child classes, I have tried to created `is_done` as > > `column_property` on parent but I couldn't make it work. Also I tried using > > `hybrid_property` and neither it is. > > > > What should I do to make Parent class get `is_done` from its children? > > > > stackoverflow link: > > https://stackoverflow.com/questions/66024558/creating-column-sqlalchemy-property-on-parent-class-based-on-child-column-proper > > > > -- > > 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 [email protected]. > > To view this discussion on the web visit > > https://groups.google.com/d/msgid/sqlalchemy/1310342569.2406235.1612346870964%40mail.yahoo.com. > > -- > 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 [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/CAFHwexdFiYC-AotO5ZNcNFLGfnYXEHmJpHB%3DWg3hQ0mCXHKu5g%40mail.gmail.com. > -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy/eb9c420b-3f51-4459-8c35-e519e59dfed9%40www.fastmail.com.
