SQLALchemy懒惰编译类

步骤是:

1) 在那之后,我编写了一个函数,它接受一个参数(类名)检查它是否尚未加载,并创建属性、外键和关系,比如 class.attrib=Column(String)

__new__ 用于创建类, __getattr__ 用于查询和可能需要 __setattr__

  def __new__(cls,*args,**kwargs):
    if cls.__name__ not in sl_loaded_classes: sl_load_function(cls.__name__)
    return super(MyCLA,cls).__new__(cls)

  def __getattr__(self,attr):
    if "MyClass" not in sl_loaded_classes: sl_load_function("NameType")
    if False: pass
    elif attr=="relation" and "RelatedClass" not in sl_loaded_classes:
      sl_load_function("RelatedClass")
      for sl_class in gc.get_objects():
        if isinstance(sl_class,self.__class__):
          config.session.refresh(sl_class)
    else: return config.Base.__getattr__(self, attr)
    return getattr(self,attr)