Question

Let’s say I have a User model which has_many :posts, while Post has_many :comments.

If I do @user.posts.map {|post| post.comments}.flatten I’ll get all the comments on the user’s posts. Is there somewhere to configure the Post or Comment model to detect it’s being referenced in the context of a specific user and only return the specific user’s comments?

That is, @user.posts.map {|post| post.comments}.flatten and @posts.map {|post| post.comments}.flatten (assuming the same posts) wouldn’t return the same number of comments (assuming multiple users are commenting).

From a previous SO question’s answers, it sounds like I want some sort of nested has_many through. Is that correct? Is there any easy way in Rails 3 to detect the ‘source’?

Answer 1

Updated answer:

Here’s a method that’ll get a post’s author’s comments

class Post < ActiveRecord::Base
  belongs_to :user   # So, there's a user_id attribute
  has_many :comments

  def authors_comments
    comments.where("user_id = ?", user_id)
  end
end

That should let you do:

@user.posts.each { |post| puts post, post.authors_comments }

it’s not as efficient as the other method, though; n posts will result in n SQL queries to get the comments. But it’s pretty close to what was described in the comment below.

---

Original answer (for posterity)

It ain’t the prettiest, but you can do something like

class User < ActiveRecord::Base
  has_many :posts    # All the user's posts
  has_many :comments # All the user's comments on all posts

  # All comments made on any of user's posts
  has_many :replies, :through => :posts, :source => :comments

  def replies_to_self
    replies.where("comments.user_id = ?", id)
  end
end

Call @user.replies_to_self to get the users’ comments to his/her own posts

You end up with SQL like this:

SELECT
    "comments".*
FROM
    "comments"
INNER JOIN
    "posts"
ON
    "comments"."post_id" = "posts"."id"
WHERE
    "posts"."user_id" = X AND "comments"."user_id" = X

(where X would be the user’s id)