Sqlalchemy: on delete set null

class Parent(Base):
 
    __tablename__ = 'parent'
 
    id=sa.Column(sa.Integer, primary_key=True)
    name=sa.Column(sa.String(), nullable=False)
    age=sa.Column(sa.Integer(), nullable=False)
    profession=sa.Column(sa.String(), nullable=False)
 
    childs = relationship("Child", back_populates='parents', passive_deletes=True)
 
    def __repr__(self):
        return f'[parent]: id="{self.id}", name="{self.name}", age="{self.age}, "profession="{self.profession}"'
 
    def __str__(self):
        return f'[parent]: id="{self.id}", name="{self.name}", age="{self.age}, "profession="{self.profession}"'
 
class Child(Base):
 
    __tablename__ = 'child'
 
    id=sa.Column(sa.Integer, primary_key=True)
    name=sa.Column(sa.String(), nullable=False)
    age=sa.Column(sa.Integer(), nullable=False)
    parent_id=sa.Column(sa.Integer, sa.ForeignKey("parent.id", ondelete='SET NULL'))
 
    parents = relationship("Parent", back_populates='childs')
 
    def __repr__(self):
        return f'[child]: id="{self.id}", name="{self.name}", age="{self.age}, parent_id={self.parent_id}'
 
    def __str__(self):
        return f'[child]: id="{self.id}", name="{self.

with my_sessionmaker() as session:
        # query = sa.delete(Parent).where(Parent.id == 1)
        # session.execute(query)
        parent = session.get(Parent, 1)
        session.delete(parent)
        session.commit()
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