python - SAWarning : Object of type <Child> not in session, 沿着 'Parent.children' 的添加操作将不会继续

Question

我被困在这个问题上，不知道如何解决。这是我的 models.py 文件:

模型.py

class TripDetail(db.Model):
    """
    Base class for every table that contains info about a trip.
    """
    __abstract__ = True
    __bind_key__ = 'instructions'

    id = db.Column(db.Integer, primary_key=True)
    # list of fields    

class Overview(TripDetail):
    """
    Class that contains general information about a trip.
    """
    __tablename__ = 'overviews'
    __table_args__ = (
        db.ForeignKeyConstraint(['user_id', 'calendar_id'], ['calendars.user_id', 'calendars.id'], ondelete='CASCADE'),
    )  # constraints on other tables, omitted here
    user_id = db.Column(db.Integer, primary_key=True)
    calendar_id = db.Column(db.Integer, primary_key=True)
    calendar = db.relationship('Calendar', backref=db.backref('overviews', cascade='delete'), passive_deletes=True)
    # other fields

class Step(TripDetail):
    __tablename__ = 'steps'

    overview_id = db.Column(db.Integer, db.ForeignKey('overviews.id', ondelete='CASCADE'))
    overview = db.relationship('Overview', backref=db.backref('steps', cascade='delete'), passive_deletes=True)
    # also other fields

这就是我将项目添加到数据库的方式(响应参数包含一个与类匹配的字典，以这种方式可以直接解包):

def add_instruction(response):
    """
    Adds a travel instruction to the database.
    """
    steps = response.pop('steps')
    overview = Overview(**response)
    for step in steps:
        Step(overview=overview, **step)
    db.session.add(overview)
    db.session.commit()
    logger.info(f"Stored instruction with PK {(overview.id, overview.user_id, overview.calendar_id, overview.event_id)}")

现在，overviews 表已正确填写，但 steps 仍为空。检查日志，我收到此警告:

SAWarning: Object of type not in session, add operation along 'Overview.steps' will not proceed (orm_util.state_class_str(state), operation, prop))

我做错了什么？

Answer 1

通常，当 add() 将对象添加到 session 时，它们的相关对象将按照您的需要自动添加。该行为由关系的 cascade 控制。 .

在 Steps.overview 中将 cascade 设置为 'delete' 会删除默认的 'save-update' ，这就是打开自动添加的原因。您可以使用cascade='save-update, delete' 将其添加回去，但请查看possible traits并查看您可能还需要什么。一个常见的集合是'all, delete-orphan'。

请记住这些是严格的 ORM 行为；在级联中设置 'delete' 不会设置列的 ON [event] CASCADE。