在Rails中建立多对多关联的正确方法是什么

Question

So I've got three models in my app, a User, Review and a Movie model. A user can review many movies (one per movie), a Movie can have many reviews from many users. Their connection is a review.

Am I doing the following setup right?

class Movie < ActiveRecord::Base
  has_many :reviews, :through => :users

end

class Review < ActiveRecord::Base
  belongs_to :user
  belongs_to :project
end

class User < ActiveRecord::Base
  has_many :reviews, :through => :movies

end

I'm hoping I can do something like:

User.reviews (which would give me back the user's reviews and the corresponding id of the movie which the review relates to)

Thanks

Answer 1

I believe this is the approach you should be taking

class User < ActiveRecord::Base
  has_many :reviews
  has_many :movies, :through => :reviews
end

class Review < ActiveRecord::Base
  belongs_to :user
  belongs_to :movie
end

class Movie < ActiveRecord::Base
  has_many :reviews
  has_many :users, :through => :reviews
end

You would also want to validate uniqueness in the model Review and/or enforce uniqueness on the join-table to only allow a single user per movie. It's up to you if you want to take this UQ constraint into the schema as well (DHH says 'Yes', I say 'the slathering of dumb persistance' is a 'No no'...)

User.reviews will give you the 'join records', ie along the lines of <Review user_id=x, movie_id=y> Certainly, you'd have a lot more columns on the join table pertaining to the review, such as :summary, :content etc. It's easy enough to access the movie from a review, ie Movie.find_by_id(User.reviews.last.movie_id).title