Rails 3 complex associations using nested_has_many_through - ruby-on-rails

Question

I have been trying to develop a movie based rails application which has support for multiple regions (Hollywood, Bollywood etc). I call the multiple regions as languages in the application.
Each language has its own set of data i.e., english has all the movies related to hollywood and language hindi has all the movies related to bollywood.
Language Model
class Language < ActiveRecord::Base
has_many :movies
has_many :cast_and_crews, :through => :movies, :uniq => true
has_many :celebrities, :through => :cast_and_crews, :uniq => true
# FIXME: Articles for celebrities and movies
has_many :article_associations, :through => :celebrities
has_many :articles, :through => :article_associations, :uniq => true
end
Here movies and celebrities both have articles using the article_association class.
Movie Model
class Movie < ActiveRecord::Base
belongs_to :language
has_many :cast_and_crews
has_many :celebrities, :through => :cast_and_crews
has_many :article_associations
has_many :articles, :through => :article_associations, :uniq => true
end
Celebrity Model
class Celebrity < ActiveRecord::Base
has_many :cast_and_crews
has_many :movies, :through => :cast_and_crews, :uniq => true
has_many :article_associations
has_many :articles, :through => :article_associations, :uniq => true
end
class ArticleAssociation < ActiveRecord::Base
belongs_to :article
belongs_to :celebrity
belongs_to :movie
end
and this is how my Article model is defined
class Article < ActiveRecord::Base
has_many :article_associations
has_many :celebrities, :through => :article_associations
has_many :movies, :through => :article_associations
end
What I am trying to achieve is language.article should return all the articles related to celebrities and movies.
The reason why I am not using SQL is find_by_sql does not support ActiveRelation and I will not be able use has_scope functionality.
I am using nested_has_many_through, has_scope and inherited_resources gems
Any help in this will be greatly appreciated.

Answer 1

Rails 3.1 now has support for nesting relations. Of course the built in one should be better then a plugin :)
http://railscasts.com/episodes/265-rails-3-1-overview

Answer 2

There are few tricks that should allow what you need, going out of Article you can query all the Moviesfor given language id
class Article < ActiveRecord::Base
has_many :article_associations
has_many :celebrities, :through => :article_associations
has_many :article_movies, :through => :article_associations, :class => 'Movie'
scope :for_language, lambda {|lang_id|
joins(
:article_associations=>[
:article_movies,
{:celebrities => { :cast_and_crews => :movies } }
]
).where(
'movies.language_id = ? OR article_movies.language_id = ?',
lang_id, lang_id
)
}
end
Then in language define a method that will use earlier scope of Article
class Language < ActiveRecord::Base
has_many :movies
has_many :cast_and_crews, :through => :movies, :uniq => true
has_many :celebrities, :through => :cast_and_crews, :uniq => true
def articles
Article.for_language id
end
end
The only unsure part here is how :article_movies will be represented in sql ...

Answer 3

ok This is what I did to fix this.
Added the following scope in my Article class
def self.region(region_id)
joins(<<-eos
INNER JOIN
(
SELECT DISTINCT aa.article_id
FROM regions r
LEFT JOIN movies m on m.region_id = r.id
LEFT JOIN cast_and_crews cc on cc.movie_id = m.id
LEFT JOIN celebrities c on c.id = cc.celebrity_id
LEFT JOIN events e on e.region_id = r.id
LEFT JOIN article_associations aa on (aa.event_id = e.id or aa.movie_id = m.id or aa.celebrity_id = c.id)
WHERE r.id = #{region_id}
) aa
eos
).where("aa.article_id = articles.id")
end
This gives me a ActiveRecord::Relation instance that I am expected which retrieves all the records for a movie, celebrity or event.
Thanks for all who helped me.
If you have any comments to improve it please comment it. Very much appreciated.