Rails：has_many：through。 需要返回具有唯一列值的记录

Question

In my User model:

has_many :followed_recommendations, :through => :followed_users, :source => :recommendations, class_name: Recommendation

A recommendation has a movie_id column. A user can get multiple recommendations for the same movie but I would like to return only 1.

So I need a way to get only the :followed_recommendations that have a unique movie_id value but not sure how to do this. The example I keep seeing coming up is:

has_many :products, -> { distinct }, through: :orders

But that is looking at the full product record whereas I just want distinct by one column.

Answer 1

你试过了吗：

 has_many :followed_recommendations, ->{group(:movie_id)}, :through => :followed_users, :source => :recommendations, class_name: Recommendation

Answer 2

You have a movie_id column in your Recommendation model, so I assume you have this association.

class Recommendation < ActiveRecord::Base
  belongs_to :movie
end

Then you could use the way with distinct like you posted in your question.

class User < ActiveRecord::Base
  has_many :followed_recommendations, :through => :followed_users, :source => :recommendations, class_name: Recommendation
  has_many :followed_recommended_movies, -> { distinct }, :through => :followed_recommendations, :class_name => Movie, source: :movie
end