关联模型的ID列表

Question

I have 3 models: Users, Articles and Comments.

• Articel has many Comments.
• Comments belongs to Article.
• User has many comments.

Textbook case :)

I would like to make a list of Article IDs where the User has made Comments on. How do I do that?

I've tried variants of User.find(1).comments.articles_ids in the console but that gives me a undefined method error.

I'm sure it's simple, but I cant't figure it out :)

Thanks!

Answer 1

One way of doing it, that works with your current setup:

user.comments.collect(&:article_id).uniq

Alternatively I guess you could add a has_many :through to User :

class User < ActiveRecord::Base
  has_many :articles, :through => :comments
end

then you can get the ids via user.articles.collect(&:id) (perhaps also user.article_ids , but I'm not sure about that).