Ruby on Rails

Hi to all.

I am working for a translation agency and I have the task to create an auto-estimate system and ordering/invoicing administration system. I am stuck on how to manage the language pairs.
I created a Language model with the language name and a LanguagePair with a source language, a target language and a rate per words attributes. I tried with:

LanguagePair
belongs_to :source, :class_name => "Language", :foreign_key => "source_id"
belongs_to :target, :class_name => "Language", :foreign_key => "target_id"

and also by replacing the source and target in the LanguagePair with a string type and loading it with a Language.all.permutation(2).to_a and eliminate the need for nesting.
In the end I will create a sort of cart and lineitem model and add the LanguagePair to the cart as a LineItem.

Is there a "best" way to do this maybe with a Language self-referential model?


thanks in advance