Rails form_for helper used the active record class for handling the forms and saving to database. However in some cases you might not want your form data to be saved in a database. For example, if you are developing an application which creates a bucket in amazon s3, you wouldn’t want your bucket name to be stored in the database, you just pass the bucket name using form and write backend controlled codes to check if the bucket exists and if not pass the form name parameter to S3 function to create a bucket. Here we wont be needing a database to save the bucket name ,because you can use other AWS sdk functions to vie, delete and lists the buckets.

So we make little tweaks to our model class to make this work. Here I have a model named demo.rb. and it looks like this.
class Demo 
  include ActiveModel::Validations
  include ActiveModel::Conversion
  extend ActiveModel::Naming
  attr_accessor :name
  validates :name , presence:true  
  def initialize(attributes ={})
    attributes.each do |name , value|
    send("#{name}=" , value)
  end
  end
In the above code the demo class is not inheriting the active record class. Instead we are including other modules like validations, conversion and we are extending Naming. These classes have to be added for the form to work properly. For example, Active model validation lets you validate your form.

Since you are posting the data from the form using hashes you need initialize method to get those values in a hash. It loops through the attributes and uses the send method to assign the data and value.

The view has the same code as it does for the normal model. It looks like this.
<%= form_for(@demo) do |f| %>
    <%= render 'shared/bucket_error_messages' %>
    <%= f.label :name%>
    <%= f.text_field :name%>
    <%= f.submit "createbucket", class:  "btn btn-default" %>    
<% end %>
In controller instead of @demo.save? you should use @demo.valid? since we are not saving the data to the database. And the code looks like this
class DemosController < ApplicationController  
  def index
   redirect_to :action => "show"
  end 
  def new
    @demo = Demo.new
  end
  def create           
        @demo = Demo.new(params[:demo])
        if @Demo.valid?   
       <your action goes here>
        end
end
The create action doesn’t save the data , instead it does the action you mention the if condition.