They seem to be runnable except the base should be DeclarativeMeta The relationships aren’t to the same target in real life,
It’s like this: Class BaseClass: ... Class SubClassA(BaseClass) ... Class SubclassB(BaseClass): ... (Plus Many other subclasses) A Mixer “BaseClassBaseClass” such that child subclassA and subclassB are both present in mix_base_class_bass_class BaseClass has relationships to BaseClass, SubClassA and SubClassB, so you can access only SubClassAs and SubClassBs or all SubClassXs that could be filtered to whatever subclass you need. All these relationships use the same mixer table, because they all share a primary key with BaseClass (and removing the need to make explicit mixed tables for every subclass). Mark Aquino ________________________________ From: sqlalchemy@googlegroups.com <sqlalchemy@googlegroups.com> on behalf of Mike Bayer <mike...@zzzcomputing.com> Sent: Thursday, December 17, 2020 7:08:58 PM To: noreply-spamdigest via sqlalchemy <sqlalchemy@googlegroups.com> Subject: Re: [sqlalchemy] Re: Can't delete cascade many-to-many with polymorphic relationships unless using lazy=dynamic your examples aren't complete or runnable so I don't really know what the issue is, although having two relationships to the same target class seems a little unusual and I'm not sure why you'd need that. On Thu, Dec 17, 2020, at 6:01 PM, maqui...@gmail.com<mailto:maqui...@gmail.com> wrote: I think I may have just found a solution? Not sure if this is correct but it looks like it worked when i changed the "extra" relationship to passive_deletes=True instead of cascade class ChildClass(XPressoBase): __tablename__ = "child_class" id = Column("id", UUID(as_uuid=True), primary_key=True, default=uuid4()) parents = relationship("ParentClass", secondary="mix_parent_class_child_class", passive_deletes=True) children = relationship("ChildChildClass", secondary="mix_child_class_child_child_class", cascade="all, delete") children2 = relationship("ChildChildClass", secondary="mix_child_class_child_child_class", passive_deletes=True) On Thursday, December 17, 2020 at 5:50:06 PM UTC-5 maqui...@gmail.com wrote: I have a polymorphic data model where association tables are to base classes and some relationships that link to different child classes to filter out the non-matching base classes, however these seem to result in sqlalchemy being unable to delete cascade properly In a real case lets say i have class Base(): children = relationship("Base", secondary="mix_base_base", cascade="all, delete") someTypes = relationship("SomeType", secondary="mix_base_base", cascade="all, delete") other_types = relationship("OtherType", secondary="mix_base_base", cascade="all") class SomeType(Base): parents = relationship("Base", secondary="mix_base_base", passive_deletes=True) class OtherType(Base): parents = relationship("Base", secondary="mix_base_base", passive_deletes=True) if I delete a base that doesn't have relationships to SomeType and OtherType, then everything works great. However once I add those extra relationships sqlalchemy no longer deletes the children relationships. This can be overcome by using lazy="dynamic" on the relationships, but at GREAT performance cost (about 100%), which isn't good. Does anyone know how to get around this without using dynamic loading? The specific relationships are important for front end pagination of data, but the performance cost is too great for the amount of data in this system to double the query times. a simplified and stupid workable example where I just add a redundant children2 relationship to ChildClass, resulting in the same problem: from uuid import uuid4 from sqlalchemy import Column from sqlalchemy.dialects.postgresql.base import UUID from sqlalchemy.orm import relationship from webapp.database.orm.base import XPressoBase class ChildClass(Base): __tablename__ = "child_class" id = Column("id", UUID(as_uuid=True), primary_key=True, default=uuid4()) parents = relationship("ParentClass", secondary="mix_parent_class_child_class", passive_deletes=True) children = relationship("ChildChildClass", secondary="mix_child_class_child_child_class", cascade="all, delete") children2 = relationship("ChildChildClass", secondary="mix_child_class_child_child_class", cascade="all, delete") class ChildChildClass(Base): __tablename__ = "child_child_class" id = Column("id", UUID(as_uuid=True), primary_key=True, default=uuid4()) parents = relationship("ChildClass", secondary="mix_child_class_child_child_class", passive_deletes=True) class ParentClass(Base): __tablename__ = "parent_class" id = Column("id", UUID(as_uuid=True), primary_key=True, default=uuid4()) children = relationship("ChildClass", secondary="mix_parent_class_child_class", cascade="all, delete") from sqlalchemy.sql.schema import Table, ForeignKey, Column, UniqueConstraint from webapp.database.orm.base import XPressoBase mix_parent_class_child_class = Table( "mix_parent_class_child_class", XPressoBase.metadata, Column("parent_class_id", ForeignKey("parent_class.id<http://parent_class.id>", ondelete="CASCADE"), nullable=False), Column("child_class_id", ForeignKey("child_class.id<http://child_class.id>"), nullable=False), UniqueConstraint( "parent_class_id", "child_class_id", name="uix_parent_class_child_class" ), ) mix_child_class_child_child_class = Table( "mix_child_class_child_child_class", XPressoBase.metadata, Column("child_class_id", ForeignKey("child_class.id<http://child_class.id>", ondelete="CASCADE"), nullable=False), Column("child_child_class_id", ForeignKey("child_child_class.id<http://child_child_class.id>"), nullable=False), UniqueConstraint( "child_class_id", "child_child_class_id", name="uix_child_class_child_child_class" ), ) -- 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. 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