title: Can't get user association working in rails
body: <p>I've been struggling to get an association working. A user <code>has_many :campaigns</code> and a campaign <code>belongs_to :user</code></p>
  
  <p>but when I try to create a new campaign, it gives me an error saying campaigns is an invalid method</p>
  
  <pre><code>def index
      @campaigns = Campaign.all.order("created_at DESC")
    end
  
    # GET /campaigns/1
    # GET /campaigns/1.json
    def show
    end
  
    # GET /campaigns/new
    def new
      @campaign = current_user.campaigns.build
    end
  
    # GET /campaigns/1/edit
    def edit
    end
  
    # POST /campaigns
    # POST /campaigns.json
      def create
      @campaign = current_user.campaigns.new(campaign_params)
  
      if @campaign.save
        redirect_to @campaign
      else
        render 'new'
      end
  </code></pre>
  
  <p>I already did all the user_id migration and stuff</p>
  
  <pre><code>class Campaign &lt; ActiveRecord::Base
      belongs_to :user
  end
  
  
  
     class User &lt; ActiveRecord::Base
  
    devise :database_authenticatable, :registerable,
           :recoverable, :rememberable, :trackable, :validatable
    has_many :campaigns
  end
  </code></pre>
  
  <p>Error Message: undefined method `campaigns' for #</p>