Personally I would make models a package rather than just a module (since you sy you have a lot of order related logic). I would create one or more modules in t

Personally I would make models a package rather than just a module (since you sy you have a lot of order related logic). I would create one or more modules in this package, presumably one of those for orders. Then I would actually create the base logic which clearly belongs to one Order instance as methods on the Order class. If you have something like "can x and y and (...)" be ordered together I would make an unbound function in your orders module which takes an iterable (Lists etc.) of Orders and works on it. Note that I am by no means a Django guru or something like that.