表(模型)与Flask SQLAlchemy的继承

Question

我按照这个问题的建议,但我仍然收到这个错误: sqlalchemy.exc.NoForeignKeysError: Can't find any foreign key relationships between 'investment' and 'real_estate'.

楷模

class Investment(db.Model):

    __tablename__ = 'investment'
    __mapper_args__ = {'polymorphic_identity': 'investment'}

    id = Column(db.Integer, primary_key=True)
    item_name = Column(db.String(64))
    investment_type = Column(db.String(32), nullable=False)
    __mapper_args__ = {'polymorphic_on': investment_type}

class RealEstate(Investment):

    __tablename__ = 'real_estate'
    __mapper_args__ = {'polymorphic_identity': 'real_estate'}
    id = Column(db.Integer, primary_key=True)
    current_balance = Column(db.Float)

我还更新了该答案中的示例,以反映SQLAlchemy文档中的更改,但仍然是错误.

这里的目标是我不希望RealEstate继承的属性在Investment表中.我想使用RealEstate表继承并保留所有这些属性.

谁能看到我错过的东西？

Answer 1

RealEstate 中的属性id必须是引用 Investment 的外键。否则，你怎么能说每一个房地产都是投资呢？

将您的 RealEstate 类定义更改为以下内容：

class RealEstate(Investment):
    __tablename__ = 'real_estate'
    __mapper_args__ = {'polymorphic_identity': 'real_estate'}
    # This id below should reference Investment. Hence, define it as foreign key. 
    id = Column(Integer, ForeignKey('investment.id'), primary_key=True)
    current_balance = Column(db.Float)