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copied!<p>You definitely can do this. The code below is using the <code>declarative_base</code>, but shows the model setup which works. <code>D</code> class is both a parent and a child using class inheritance. However, the <code>polymorphic_identity</code> is stored only on the top level. Make sure you have all proper foreign keys and class inheritances set up.</p> <p>*Note: you example defines type_id as Numeric, however the values seem to be Strings.*</p> <pre><code>Base = declarative_base(cls=_BaseMixin) Base.query = session.query_property() class BaseModel(Base): __tablename__ = 'entities' id = Column(Integer, primary_key=True) #type_id = Column(Integer, nullable=False) type_id = Column(String, nullable=False) __mapper_args__ = { 'polymorphic_identity': 'entity', 'polymorphic_on':type_id, 'with_polymorphic':'*' } class ModelB(BaseModel): __tablename__ = 'modelB' __mapper_args__ = {'polymorphic_identity': 'modelB'} id = Column(Integer, ForeignKey('entities.id'), primary_key=True) name = Column(String, nullable=False) class ModelC(BaseModel): __tablename__ = 'modelC' __mapper_args__ = {'polymorphic_identity': 'modelC'} id = Column(Integer, ForeignKey('entities.id'), primary_key=True) name = Column(String, nullable=False) class ModelD(BaseModel): __tablename__ = 'modelD' __mapper_args__ = {'polymorphic_identity': 'modelD'} id = Column(Integer, ForeignKey('entities.id'), primary_key=True) name = Column(String, nullable=False) class ModelE(ModelD): __tablename__ = 'modelE' __mapper_args__ = {'polymorphic_identity': 'modelE'} id = Column(Integer, ForeignKey('entities.id'), ForeignKey('modelD.id'), primary_key=True) name = Column(String, nullable=False) class ModelF(ModelD): __tablename__ = 'modelF' __mapper_args__ = {'polymorphic_identity': 'modelF'} id = Column(Integer, ForeignKey('entities.id'), ForeignKey('modelD.id'), primary_key=True) name = Column(String, nullable=False) </code></pre>

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