Ruby on Rails

This can be done only with a custom method validation, Such as           class Comment        include Mongoid::Document        include Mongoid::Timestamps         include ActiveModel::Validations              validate :must_be_friends              def must_be_friends           errors.add(:base, 'Must be friends to leave a comment') if hash[:firstname].nil?        end     end

I was working on uploading images using paperclip gem . I wanted to use Ajax. I googled a lot, But every result says its not possible, that  you can't upload images using Ajax. Some Jquery plug-ins are available, But its not behaving like what I really needed in my project. Finally I got the solution for this problem. It is a common solution. First of all download the the js code and save it as jquey.form.js in assets/javascripts. Include in application.js like     //= require jquery.form Next is your view. Which may look like this     <div id="image_view">       <%=image_tag @model.image_ attr_name .url %>     </div> Next is your form to upload image [You can use bootstrap modal to render this form. Then it'll be more beautiful]     <%=form_for @model, :html => { :multipart => true, :id => "form_id" }, :url => url_for(:controller => 'controller...