在Python中，使用变量的方式在速度，CPU，内存等方面更有效率？(Which way of using variables is more efficient in terms of speed, cpu, memory, etc in python?)

 字段element_type设置为父类，因为ActiveRecord期望您在从其他模型派生时使用单表继承。 该字段将引用基类，因为它引用了存储每个实例的表。 
 
 如果CachedElement存储在它们自己的表中，那么使用Ruby模块替换继承的使用可能会更有帮助。 在类之间共享逻辑的标准方法是使用混合而不是继承。 例如： 
 
module Cacheable
  # methods that should be available for all cached models
  # ...
end

class Outcome < ActiveRecord::Base
  include Cacheable
  # ... 
end
 
 您现在可以轻松地使用多态关联，并将element_type设置为正确的类。 

The field element_type is set to the parent class because ActiveRecord expects you to use single-table inheritance when deriving from other models. The field will reference the base class because it refers to the table that each instance is stored in.
 
If the children of CachedElement are stored in their own tables, it may be more helpful to replace the use of inheritance with the use of Ruby modules. The standard approach for sharing logic between classes is to use mix-ins instead of inheritance. For example:
 
module Cacheable
  # methods that should be available for all cached models
  # ...
end

class Outcome < ActiveRecord::Base
  include Cacheable
  # ... 
end
 
You can now easily use polymorphic associations as you have been doing already, and element_type will be set to the proper class.