Rails 3: Instance variable not working as charge amount for Stripe?

Question

I'm adding Stripe to my Rails 3 app to accept credit card payments, and I'm trying to use an instance variable, "@total", for the amount to be charged to the customers.

Here's what I currently have in my model:

class Video < ActiveRecord::Base
  attr_accessible :age, :category, :description, :ethnicity, :gender, :genre, :interest, :length, :panda_video_id, :size, :tagline, :title, :video_id, :stripe_card_token
  attr_writer :current_step
  attr_accessor :stripe_card_token
  serialize :size
  serialize :age
  serialize :gender
  serialize :ethnicity

  has_many :audiences, :dependent => :destroy
  accepts_nested_attributes_for :audiences, :allow_destroy => true

  #validates_presence_of :panda_video_id, :if => lambda { |o| o.current_step == "upload" }

  def panda_video
    @original_video ||= Panda::Video.find(panda_video_id)
  end

  def save_with_payment
  if valid?
    charge = Stripe::Charge.create(
    amount: @total,
    currency: "usd",
    card: stripe_card_token
    )
  end
rescue Stripe::InvalidRequestError => e
  logger.error "Stripe error while creating charge: #{e.message}"
  errors.add :base, "There was a problem with your credit card."
  false
end

  def current_step
    @current_step || steps.first
  end

  def steps
    %w[upload info audience review]
  end

  def next_step
    self.current_step = steps[steps.index(current_step)+1]
  end

  def previous_step
    self.current_step = steps[steps.index(current_step)-1]
  end

  def first_step?
    current_step == steps.first
  end

  def last_step?
    current_step == steps.last
  end

  def all_valid?
    steps.all? do |step|
        self.current_step = step
        valid?
    end
  end
end

I contacted Stripe support, and they said that the instance variable should be working here. So, I suspect the problem lies with my controller:

class VideosController < ApplicationController
  def index
    @videos = Video.all
  end

  def show
    @video = Video.find(params[:id])
    @original_video = @video.panda_video
    @h264_encoding = @original_video.encodings["h264"]
  end

  def new
    session[:video_params] ||= {}
    @video = Video.new(session[:video_params])
    @video.current_step = session[:video_step]
  end

  def create
    session[:video_params].deep_merge!(params[:video]) if params[:video]

    #Save total value and audience form to session.
    @total = session[:video_params]["size"].collect(&:to_i).sum - 10 if session[:video_params]["size"]
    @audiences = session[:video_params].slice("size", "gender", "age", "ethnicity").to_json

    @video = Video.new(session[:video_params])
    @video.current_step = session[:video_step]
    if @video.valid?
        if params[:back_button]
            @video.previous_step
        elsif @video.last_step?
            @video.save if @video.all_valid? && @video.save_with_payment
        else
            @video.next_step
        end
        session[:video_step] = @video.current_step
    end
    if @video.new_record?
        render "new"
    else
        session[:video_step] = session[:video_params] = nil
        flash[:notice] = "Video saved"
        redirect_to @video
    end
  end

  def edit
    @video = Video.find(params[:id])
  end

  def update
    @video = Video.find(params[:id])
    if @video.update_attributes(params[:video])
      redirect_to @video, :notice  => "Successfully updated video."
    else
      render :action => 'edit'
    end
  end

  def destroy
    @video = Video.find(params[:id])
    @video.destroy
    redirect_to videos_url, :notice => "Successfully destroyed video."
  end
end

My rails app is a multi-step form, where all the data is stored in a session. @total sums up the input values in the audience step of the form, and then that @total number shows up in the final step, where the customer enters their payment info. The @total number currently shows up on this page, but for some reason Stripe can't process it, since I keep getting the following error:

Stripe error while creating charge: Missing required param: amount

What am I doing wrong here?

Answer 1

I guess, controller instance variables are not available in models. Check the solution posted to this question Ruby on Rails - Access controller variable from model.

UPDATE

You don't need to follow the example mentioned in the URL. You can directly pass the @total variable as an argument like this

#model
def save_with_payment(total)
  ...
  charge = Stripe::Charge.create(
  amount: total,
  currency: "usd",
  card: stripe_card_token
  )
  ...
end

# controller

def create
...
    if params[:back_button]
        @video.previous_step
    elsif @video.last_step?
        @video.save if @video.all_valid? && @video.save_with_payment(@total)
    else
        @video.next_step
    end
...
end

Answer 2

Im not sure because I cannot see your model code but I suspect this is because you have no attr_accessor set for :total, so attr_accessor :total in the modal and see what happens. unless i have a better idea (see your code) about how your payment process is structured I cant really give a solid answer on the matter. By you can check out http://railstips.org/blog/archives/2006/11/18/class-and-instance-variables-in-ruby/ to see if you find something that works for you.

EDIT

I though you were talking about model instance variable, you have to pass the instance variable from the controller to the model. Below is an example.

Controller snippet

...
@video.save if @video.all_valid? && @video.save_with_payment(@total)
...

Model snippet

...
def save_with_payment(total)
 if valid?
  charge = Stripe::Charge.create(
   amount: total,
   currency: "usd",
   card: stripe_card_token
  )
end