Join model between three models, has_many :through with parameters (add join condition)

I have a join model (context) that ties three models together (files, versions, sentences). Sentences have a translation.

translation <-- sentences
                    >
                    >
       files----(context)----versions

files-> has_many :sentences, :through => :contexts
sentences -> belongs_to :translation

I want to get all sentences and their translations for a file for a given version. I want to do it with eager loading, to feed the view with the whole set and not have additional queries.

If I do file.sentences.find(:all,:include => :translation) I get all of them (for all versions). If I add conditions, say 'version_id = 2', then they applied to all records, not to the join and I lose the untranslated sentences.

I've made it work by adding at runtime, right before the .find(), a has_many relationship, like this:

Files.has_many "sentences_by_version_#{vid}".to_sym,:class_name => 'Context',:conditions => ['contexts.versio_id = ?',vid]

And then including :sentences_by_version_2 (or whatever id's value is).

Is there a cleaner way to do this with eager loading? The has_many has to be created everytime. Maybe overloading a method of my class and using a lambda? Any ideas?

I need to get the sentences (with outer join), not the contexts, because that yields the sentences that are not translated. So, somehow I need to push a condition on the join.

Thanks, Eduardo.