Question

我对SQLAlchemy不熟悉，并且在涉及外键时如何创建hybrid_property表达式有点困惑。以下是我正在使用的声明性类：

class ProductColor(Base):
    __tablename__ = 'productcolor'
    value = Column(Text, nullable=False, unique=True)
    rgb = Column(Text, nullable=False)
    cmyk = Column(Text)


class ProductVariant(Base):
    __tablename__ = 'productvariant'
    product_id = Column(Integer, ForeignKey('product.id'),
                        nullable=False)
    product = relationship('Product', backref='variants')
    color1_id = Column(Integer, ForeignKey(ProductColor.id), nullable=False)
    color1 = relationship(ProductColor, foreign_keys=color1_id)
    color2_id = Column(Integer, ForeignKey(ProductColor.id))
    color2 = relationship(ProductColor, foreign_keys=color2_id)
    is_display_color = Column(Boolean, default=False)

    @hybrid_property
    def slug(self):
        return u''.join((self.color1.value, getattr(self.color2, 'value', '')))

    @slug.expression
    def slug(cls):
        pass # What do i write here?

实例属性工作正常，但我不确定要在表达式属性中放入什么。我尝试了以下内容，但它给了我AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object associated with ProductVariant.color1 has an attribute 'value'：

@slug.expression
    def slug(cls):
        return cls.color1.value + cls.color2.value

修改

我也尝试过以下内容，然后获取AttributeError: 'str' object has no attribute 'corresponding_column'：

@slug.expression
def slug(cls):
    color1 = aliased(ProductColor, 'color1')
    color2 = aliased(ProductColor, 'color2')
    return (select([func.concat(color1.value, color2.value)])
            .join(color1).filter(color1.value == cls.color1.value)
            .outerjoin(color2).filter(color2.value == cls.color2.value)
            .as_scalar())

你们对此有什么好的解决方案吗？

带有外键的SQLAlchemy hybrid_property表达式

0 个答案: