Question

I am currently building very simple Comment system on Rails. The primary models are User, Albumpost, and Comment. Users can post Albumposts. For each Albumpost, Users can add Comments to the Albumpost. As a result, a Comment belongs to a User and belongs to an Albumpost.

The problem I’m having is that even with the proper associations in my models (see below), I can’t get

@comment.user.name

when I’m trying to render the comments in the albumpost ‘show’ page (/views/albumposts/show.html.erb). When I go to the page, I can’t get @comment.user.name (doesn’t understand the association) and get a

"undefined method `name' for nil:NilClass"

Oddly I can get

@comment.albumpost.content

I’ve double-checked my models and also added the proper foreign keys to the models. Am I doing something wrong in the controllers?

Here are my models:

class Comment < ActiveRecord::Base
  attr_accessible :body, :albumpost_id, :user_id
  belongs_to :albumpost
  belongs_to :user
end

class Albumpost < ActiveRecord::Base
  attr_accessible :content
  belongs_to :user
  has_many :comments, dependent: :destroy
end

class User < ActiveRecord::Base
  attr_accessible :name, :email, :password, :password_confirmation
  has_many :albumposts, dependent: :destroy
  has_many :comments, dependent: :destroy
end

Here are the relevant parts of my Albumpost and Comments controllers:

class AlbumpostsController < ApplicationController
  def show
    @albumpost = Albumpost.find(params[:id])
    @comments = @albumpost.comments
    @comment = Comment.new
    @comment.albumpost_id = @albumpost.id
    @comment.user_id = current_user.id
  end
end

class CommentsController < ApplicationController
  def create
    albumpost_id = params[:comment].delete(:albumpost_id)
    @comment = Comment.new(params[:comment])
    @comment.albumpost_id = albumpost_id
    @comment.user_id = current_user.id
    @comment.save
    redirect_to albumpost_path(@comment.albumpost)
  end
end

Answer 1

I think you should prefer setting objects to relations instead of setting their ids. For example, you should do this:

 @comment.user = current_user

instead of

 @comment.user_id = current_user.id

ActiveRecord will take care of setting corresponding *_id fields. I’m not sure how it handles the reverse. (it should autoload though, if I understand correctly)