通过关系名称 (str) 或对象动态添加 sqlalchemy 关系

Question

我正在解析深度嵌套的 XML 分层文件并使用 SQLAlchemy 将数据保存到 PostgreSQL。解析文件中的每个树非常简单：获取元素属性，根据命名映射对其进行重命名，创建 SQLA 对象，解析子元素，添加适当的关系（父子元素），然后重复。

为了避免样板代码，我正在尝试实现递归解决方案。到目前为止，我已经成功地实现了 SQLA 对象列表的创建，但现在努力根据预先确定的辅助字典动态添加关系（例如，我将明确说明要创建哪个关系）

非常简短的示例

<ApplicationSessionStart TradeId="085747" EventTime="2021-05-02T09:00:00">
  <LotList>
      <LotInfo LotNumber="1"/>
   </LotList>
</ApplicationSessionStart>

SQLA 类with 关系：

class ApplicationSessionStart(Base):
    __tablename__ = "application_session_start"
    id = Column(Integer, primary_key=True, autoincrement="auto")
    trade_id_etp = Column(String(100), nullable=False)
    event_time = Column(DateTime, nullable=False)

    # Relationships

    lot_info = relationship(
        "LotInfo",
        back_populates="application_session_start",
        uselist=True,
    )

class LotInfo(Base):
    __tablename__ = "lot_info"
    id = Column(Integer, primary_key=True, autoincrement="auto")
    lot_number = Column(String(5), nullable=True)

    # FKs
    application_session_start_id = Column(
        Integer,
        ForeignKey("application_session_start.id"),
    )

    # Relationships
    application_session_start = relationship(
        "ApplicationSessionStart",
        back_populates="lot_info",
        uselist=True,
    )

描述 XML 数据逻辑的辅助字典 结构

gdm = {
    "ApplicationSessionStart": {
        "model": ApplicationSessionStart,
        "children": {LotInfo: "LotInfo.application_session_start"},
        "naming": {
            "EventTime": "event_time",
            "TradeId": "trade_id",
        },
    },
    "LotInfo": {
        "model": LotInfo,
        "children": None,
        "naming": {"LotNumber": "lot_number"},
    },
}

递归创建对象的

def rec_create_class_from_elem(elem, gdm, result_list=None):
    elem_name = elem.tag
    expected_children = gdm.get(elem_name).get("children")

    if result_list is None:
        result_list = []

    elem_attrs_dict = elem.attrib
    elem_correct_dict = map_naming_v2(elem_name, gdm, elem_attrs_dict)
    model = gdm.get(elem_name).get("model")
    obj = model(**elem_correct_dict)
    result_list.append(obj)
        
    if expected_children is not None:
        for k, v in expected_children.items():
            model_name_str = k.__name__
            for child in elem.findall(".//" + model_name_str):
                rec_create_class_from_elem(child, gdm, result_list)

    return result_list

函数

[、]

Answer 1

我发现通过调用 setattr 可以做到这一点

setattr(obj, relationship, [parent_obj])