title: has_one relationship is resulting in ActiveModel::MissingAttributeError , what am I missing here?
body: <p>I feel like I am overlooking something obvious here.  I can create a story model, and a category model, but I can't relate a story to a category.  </p>
  
  <p>Here is how I reproduce the error: </p>
  
  <pre><code>s = Story.new(title: "test", picture_url: "www.google.com") 
  c = Category.last
  s.category = c
  </code></pre>
  
  <p>error: ActiveModel::MissingAttributeError: can't write unknown attribute `story_id'</p>
  
  <p>Story model</p>
  
  <pre><code>class Story &lt; ActiveRecord::Base
   has_many :chapters, dependent: :destroy
   has_many :users, through: :story_roles
   has_one :category
  end
  </code></pre>
  
  <p>Story migration file</p>
  
  <pre><code>class CreateStories &lt; ActiveRecord::Migration
    def change
      create_table :stories do |t|
        t.string :title
        t.string :picture_url
        t.integer :category_id
  
        t.timestamps
      end
    end
  end
  </code></pre>
  
  <p>Category model </p>
  
  <pre><code>class Category &lt; ActiveRecord::Base
    belongs_to :story
    validates_presence_of :body
  end
  </code></pre>
  
  <p>Category migration</p>
  
  <pre><code>class CreateCategories &lt; ActiveRecord::Migration
    def change
      create_table :categories do |t|
        t.string :body
        t.timestamps
      end
    end
  end
  </code></pre>