Rails polymorphic comments undefined method user_n

So I followed the Railscast 154 about implementing polymorphic associations and I was able to get it up and running, but whenever I try to call the user who commented I get an undefined method.

Here's my Migration:

class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.text :content
      t.belongs_to :commentable, polymorphic: true
      t.references :member

      t.timestamps
    end
    add_index :comments, [:commentable_id, :commentable_type]
    add_index :comments, :member_id
  end
end

CommentsController:

class CommentsController < ApplicationController

before_filter :authenticate_member!
before_filter :load_commentable

  def create
    @comment = @commentable.comments.new(params[:comment])
    if @comment.save
      redirect_to :back
    else
      render :new
    end
  end

  def destroy
    @comment = Comment.find(params[:id])
    @comment.destroy

    if @comment.destroy
      redirect_to :back
    end
  end

  private

  def load_commentable
    klass = [Status, Medium].detect { |c| params["#{c.name.underscore}_id"] }
    @commentable = klass.find(params["#{klass.name.underscore}_id"])
  end

MediaController:

def show
    @medium = Medium.find(params[:id])
    @commentable = @medium
    @comments = @commentable.comments
    @comment = Comment.new
    respond_to do |format|
      format.html # show.html.erb
      format.json { render json: @medium }
    end
end

Comments Form:

<% @comments.each do |comment| %>
    <div class="comments">
        <span class="content">
            <%= comment.member.user_name %>
            <%= comment.content %>
        </span>
        <span class="comment_del">
            <%= link_to image_tag("delete-6-icon.png"), [@commentable, comment], method: :delete, data: { confirm: 'Are you sure?' } %>
        </span>
    </div>
<% end %>

Anyone know why this might be happening because I'm stuck. Thanks.

Alright I solved my own problem. The problem is that no member was associated with the comment. I had to modify my create action in the comments_controller:

def create
    @comment = @commentable.comments.new(params[:comment])
    @comment.member = current_member
    if @comment.save
      redirect_to :back
    else
      render :new
    end
end