Question

我按照question中的建议，但我仍然收到此错误： sqlalchemy.exc.NoForeignKeysError: Can't find any foreign key relationships between 'investment' and 'real_estate'.

模型

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的文档中的更改，但仍然是错误。

这里的目标是我不希望RealEstate继承的属性在投资表中。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id属性必须是引用Investment的外键。否则，你怎么能说每个RealEstate都是投资？

将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)

表（模型）与Flask SQLAlchemy的继承

1 个答案: