Question

I am using a has many through association as follows:

class Rating < ActiveRecord::Base  
  has_many :recommendation_ratings, :dependent => :destroy
  has_many :recommendations, :through => :recommendation_ratings
end

class Recommendation < ActiveRecord::Base  
  has_many :recommendation_ratings, :dependent => :destroy
  has_many :ratings, :through => :recommendation_ratings
end

class RecommendationRating < ActiveRecord::Base  
  validates :recommendation_id, presence: true
  validates :rating_id, presence: true

  belongs_to :recommendation
  belongs_to :rating
end

I am currently creating my associations in my controller as follows:

   rr   = RecommendationRating.find_by_recommendation_id(recommendation_id)
   rr ||= RecommendationRating.new(recommendation_id: recommendation_id)

   rr.rating_id = rating_id
   rr.save

Alternatively, I could assign ratings to recommendations like so:

   @recommendation = Recommendation.find(recommendation_id)
   @rating = Rating.find(rating_id)
   @recommendation.ratings << @rating

Which is the correct method to associate these records, and is there a downside to doing it the first way?

Answer 1

That depends on what you need.

The first one updates a recommendation_rating record if it already exists and enables you to run callbacks and validation after calling save

The second one creates a rating everytime you call << and it creates the record directly on the database so no validation and callback is triggered.