Rails - Jul 2008 - 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.

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