Topic: Composite foreign_key work around?

Hi all, this is my first post. I am a Rails newbie and have not had any success in finding a solution to this issue. I am connecting to an Oracle database for which I can only read (cannot write)--it's a reporting app for K-12 student data. Most of my tables join on simple id columns, but  I have a relationship between two tables which join on a composite of 3 columns (year_id, school_id, and period_number).

In C# I would simply create a datatable from a query, but in Rails, I don't know what my options are. It seems that composite foreign keys are not supported. Perhaps create a model from a query? Not sure how to do that.

Any suggestions would be much appreciated.