How to associate a Devise User with another existing model? - ruby-on-rails

Question

I am very new to Ruby on Rails and have setup Devise for authentication. I have an existing model that I created prior to adding Devise. That model is called Article. I believe I have done everything I need to do in order to use the association=(associate) method that "assigns an associated object to this object. Behind the scenes, this means extracting the primary key from the associate object and setting this object’s foreign key to the same value" which is exactly what I need to do.
Here is Devise's User model:
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
has_one :article
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
end
Here is my Article model:
class Article < ActiveRecord::Base
belongs_to :user
validates :name, presence: true, length: { minimum: 5 }
end
Here is my migration:
class AddUserRefToArticles < ActiveRecord::Migration
def change
add_reference :articles, :user, index: true
end
end
Here is my create method from my articles_controller.rb:
def create
#article.user = current_user
#article = Article.new(post_params)
if #article.save
redirect_to #article
else
render 'new'
end
end
And here is what happens when my controller runs:
NoMethodError in ArticlesController#create
undefined method `user=' for nil:NilClass
The highlighted code is #article.user = current_user. I was at least glad to know that I wrote that line of code similar to the popular answer in the Devise how to associate current user to post? question that I saw on here before posting this one.
I know I'm making a rookie mistake. What is it?

Answer 1

A new User instance needs to be assigned to #article before you can access any of the instance's attributes/associations. Try the following:
#article = Article.new(post_params) # Assign first
#article.user = current_user # Then access attributes/associations
The code posted in the question yields a nil:NilClassexception because the user association is being invoked on #article, which is nil because nothing has yet been assigned to it.