Aggregate Models that don't correspond directly to DB table


I am having trouble deciding whether to make some classes part of the
model or the controller.

These objects will represent rollups of various joined database tables.
I want to use them to build up a tree structure to make it easier to
drill through reports compiled over hundreds of thousands of database

I don’t want to persist the rollups. I just want to store them in the
session hash.

I plan to use ActiveRecord::Base.connection.select_all inside the
objects to populate themselves.

Are these objects part of the Model or the Controller?