create_link_method.rb

def create
    topic = params[:topic_name]
    @topic = Topic.find(params[:topic_val]) if params[:topic_val]!=""

    if topic != "" and params[:link][:url_link]!= ""  and data=check_url

      if @link= Link.find_by_url_link(params[:link][:url_link])
        #after upgrading to rails4 use this line instead of previous line:)
        #if @link= Link.find_by url_link: params[:link][:url_link]
        if @link.topics.exists? slug: topic.parameterize
          flash[:notice]="Link already submitted to the topic"
        else 
          @link_user = @link.link_with_topic!(topic, current_user,@topic)
          if params[:comment_body] != ""
            comment = @link.comments.build(body: params[:comment_body])
            comment.user = current_user
            comment.save
          end


          flash[:success]="Link submitted"
          publish_to_fb
        end
      else
        @link = current_user.links.build(params[:link]) 

        unless /youtube.com|vimeo.com|twitter.com|soundcloud.com/.match(params[:link][:url_link])
          img = link_image(data)
          if img
            @link.picture = img if /^(http|https):\/\/|[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,6}(:[0-9]{1,5})?(\/.*)?$/.match(img)

          end
          if data.xpath('//meta[@property="og:description"]').first
            @link.description = data.xpath('//meta[@property="og:description"]').first.attribute('content').value
          elsif data.xpath('//meta[@name="description"]').first 
            @link.description = data.xpath('//meta[@name="description"]').first.attribute('content').value
          end
        end

        if @link!= nil && @link.save
          @link_user = @link.link_with_topic!(topic, current_user, @topic)
          publish_to_fb
          if params[:comment_body] != ""
            comment = @link.comments.build(body: params[:comment_body])
            comment.user = current_user
            comment.save
          end
          flash[:success]="Link submitted"
          publish_to_fb
        end
      end
    else 
      flash[:error]= "Enter a proper url with topic name"

    end
    respond_to do |format|
      format.html { redirect_to root_url }
      format.js
    end
  end