Class B

test/orm/test_deferred.py:2791–2794

            bs = relationship("B")

        class B(Base):
            __tablename__ = "b"
            id = Column(Integer, primary_key=True)
            a_id = Column(ForeignKey("a.id"))

        A.b_count = deferred(
            select(func.count(1)).where(A.id == B.a_id).scalar_subquery()