Question

I’m making a url shortener as a learning exercise. In addition to a Visit model (which isn’t important for this question), it has a Url and a Link model, which I have joined with associations. The Url class belongs to Link, and the Link class has_one :url.

In short, the problem is that when I call the shorten method in the Link class (from the create method in the Url controller), I’m getting this error message

undefined method `link' for #<ActiveRecord::Relation:0x00000102f648b8>

The application trace points to this line in the ‘shorten’ method of the Link class (copied below)

return url.link if url 

So, I understand this error to mean that I can’t call ‘link’ on ‘url.’ However, I thought that the associations I created would allow me to do so. Can you explain what I’m doing wrong

Relevant Code

Form in new

<%= simple_form_for @url do |f| %>
  <%= f.input :original,  :label => 'Original Link', :input_html => { :maxlength => 70 } %>
  <%#= f.input :custom,  :label => '(Optional) Create your own custom shortened link ' %>
  <%= f.button :submit %>
<% end %>

Create method url controller

def create
    @url = Url.new(params[:url])
    @link = Link.shorten(@url) 

    respond_to do |format|
      if @url.save
        format.html { redirect_to action: "index", notice: 'Url was successfully created.' }
        format.json { render json: @url, status: :created, location: @url }
      else
        format.html { render action: "new" }
        format.json { render json: @url.errors, status: :unprocessable_entity }
      end
    end

  end

Url Class

class Url < ActiveRecord::Base
  attr_accessible :original

  belongs_to :link
end

Link class with shorten method

class Link < ActiveRecord::Base
  attr_accessible :identifier
  has_one :url
  has_many :visits


  def self.shorten(original, custom=nil)
    url = Url.find_by_original(original) 

    return url.link if url        #this is the problem line
    link = nil
    if custom
      raise 'Someone has already taken this custom URL, sorry' unless Link.find(:identifier => custom).nil?  #this  Link.find
      raise 'This custom URL is not allowed because of profanity' if DIRTY_WORDS.include? custom
      transaction do |txn|
        link = Link.new(:identifier => custom)
        link.url = Url.create(:original => original)
        link.save        
      end
    else
      transaction do |txn|
        link = create_link(original)
      end    
    end
    return link
  end

Answer 1

You are passing @url to Link.shorten before it is created. So you are calling the link method on a nil object.

You need to place it after @url.save if you want it to work.