Question

I have users, posts and comments. User can post only one comment to each post.

class User < ActiveRecord::Base
  has_many :posts
  has_many :comments
end

class Post < ActiveRecord::Base
  has_many :comments
  belongs_to :user
end

class Comment < ActiveRecord::Base
  belongs_to :user
  belongs_to :post
end

On userpage (http://host/users/1 for example) I want to show all posts where the given user has commented. Each post then will have all other comments.

I can do something like this in my User controller:

def show
  @user = User.find(params[:user_id])
  @posts = []
  user.comments.each {|comment| @posts << comment.post}
end

This way I will find User, then all his comments, then corresponding post to each comment, and then (in my view) for each post I will render post.comments. I’m totally new in Rails, so I can do this =) But I think it’s somehow bad and there is a better way to do this, maybe I should use scopes or named_scopes (don’t know yet what this is, but looks scary).

So can you point me out to the right direction here?

Answer 1

You could define an association which retrieves all the posts with comments in a single query. Keeping it in the model reduces the complexity of your controllers, enables you to reuse the association and makes it easier to unit test.

class User < ActiveRecord::Base
  has_many :posts_with_comments, :through => :comments, :source => :post
  # ...
end

:through is an option for has_many to specify a join table through which to perform the query. We need to specify the :source as Rails wouldn’t be able to infer the source from :post_with_comments.

Lastly, update your controller to use the association.

def show
  @user  = User.find(params[:user_id])
  @posts = @user.posts_with_comments
end

To understand more about :through and :source take a look at the documentation.