表（模型）用Flask SQLAlchemy继承 [英] Table(Model) Inheritance with Flask SQLAlchemy

问题描述

我遵循这个问题的建议，但是我仍然收到这个错误：
sqlalchemy.exc.NoForeignKeysError：在'投资'和'real_estate'之间找不到任何外键关系。


模特 $ b <$ p $投资（db.Model）：

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

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}
$ b $ class RealEstate（投资）：

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

我也更新了这个答案中的例子，以反映SQLAlchemy的文档中的变化，但仍然是错误。 目标这里是我不希望由RealEstate继承的属性在投资表。我想继承和保留RealEstate表的所有这些属性。

任何人都可以看到我错过了什么？

id 属性必须是引用投资的外键。否则，你怎么能说每个RealEstate都是一项投资？

将您的RealEstate类定义更改为以下内容：

  class RealEstate （投资）：
 
 __tablename__ ='real_estate'
 __mapper_args__ = {'polymorphic_identity'：'real_estate'} 
＃下面的id应该引用Investment。因此，将其定义为外键。 
 id = Column（Integer，ForeignKey（'investment.id'），primary_key = True）
 current_balance = Column（db.Float）
  

I followed the advice in this question but I'm still receiving this error: sqlalchemy.exc.NoForeignKeysError: Can't find any foreign key relationships between 'investment' and 'real_estate'.

Models

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)

I also updated the examples in that answer to reflect changes in SQLAlchemy's docs but, still, the error.

The goal here is that I don't want the attributes inherited by RealEstate to be in the Investment table. I would like to inherit and retain all of these attributes with the RealEstate table.

Can anyone see what I missed?

解决方案

The id attribute in RealEstate must be a foreign key referencing the Investment. Otherwise, how can you say that every RealEstate is an investment ?

Change your RealEstate class definition to the following:

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)

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