Question

鉴于sqlalchemy中有几个简单的一对多关系表，我试图编写一个通用函数来将子句添加到关系集合中。表格如下所示：

class StockItem(Base):

    __tablename__ = 'stock_items'

    stock_id = Column(Integer, primary_key=True)
    description = Column(String, nullable=False, unique=True)
    department = Column(String)
    images = relationship('ImageKey', backref='stock_item', lazy='dynamic')

    def __repr__(self):
        return '<StockItem(Stock ID:{}, Description: {}, Department: {})>'.\
            format(self.stock_id, self.description, self.department)


class ImageKey(Base):

    __tablename__ = 'image_keys'

    s3_key = Column(String, primary_key=True)
    stock_id = Column(Integer, ForeignKey('stock_items.stock_id'))

    def __repr__(self):
        return '<ImageKey(AWS S3 Key: {}, Stock Item: {})>'.\
            format(self.s3_key, self.stock_id)

因此，对于给定的设置，我可以将images集合中的项目添加到给定的StockItem：

item = StockItem(stock_id=42, description='Frobnistication for Foozlebars', 
                 department='Books')
image = ImageKey(s3_key='listings/images/Frob1.jpg', stock_id=42)
item.images.append(image)

确定。到现在为止还挺好。实际上，我的应用程序将有几个关系表。当我尝试将其概括为处理任意关系的函数时，我的问题就出现了。这就是我写的内容（注意，add_item()只是一个用try/except包装对象构造来处理IntegrityError的方法：

@session_manager
def _add_collection_item(self, Parent, Child, key, collection,
                         session=None, **kwargs):
    """Add a Child object to the collection object of Parent."""
    child = self.add_item(Child, session=session, **kwargs)
    parent = session.query(Parent).get(key)
    parent.collection.append(child)  # This line obviously throws error.
    session.add(parent)

我将这个函数称为：

db._add_collection_item(StockItem, ImageKey, 42, 'images',
                        s3_key='listings/images/Frob1.jpg',
                        stock_id=42)

这显然是错误，因为父表没有collection属性。回溯：

Traceback (most recent call last):
  File "C:\Code\development\pyBay\demo1.py", line 25, in <module>
    stock_id=1)
  File "C:\Code\development\pyBay\pybay\database\client.py", line 67, in add_context_manager
    result = func(self, *args, session=session, **kwargs)
  File "C:\Code\development\pyBay\pybay\database\client.py", line 113, in _add_collection_item
    parent.collection.append(child)
AttributeError: 'StockItem' object has no attribute 'collection'

我认为无论如何都会抛出错误，因为集合名称是作为字符串传递的。

所以我的问题是，如何通过关键词而不是使用'dot'表示法将项目添加到集合中？

Answer 1

执行：

  getattr(parent, collection).append(child)

更多信息

不使用点表示法

1 个答案: