in django i separate model components into different files and then mixin in the relevant fields and methods. for example, suppose i define models Blog and Post in blog.py, and Rating and RatingMixin (extends object not base model). I'd give Rating a method, say Initialize, that gets called when importing the whole models folder. Rating.Initialize() would then mixin all the fields and methods in RatingMixin to the specified models. In this case, it might be useful to give Blog and Post the method "average_method".

Is this good practice?

Also, what's the advantage of keep lots of data in a single row versus multiple tables? Does it effect performance that much (esp with caching)?