pep8/flake8
- The :mod:`sqlalchemy.ext.automap` extension will now set
``cascade="all, delete-orphan"`` automatically on a one-to-many
relationship/backref where the foreign key is detected as containing
one or more non-nullable columns.  This argument is present in the
keywords passed to :func:`.automap.generate_relationship` in this
case and can still be overridden.  Additionally, if the
:class:`.ForeignKeyConstraint` specifies ``ondelete="CASCADE"``
for a non-nullable or ``ondelete="SET NULL"`` for a nullable set
of columns, the argument ``passive_deletes=True`` is also added to the
relationship.  Note that not all backends support reflection of
ondelete, but backends that do include Postgresql and MySQL.
fixes #3210