Stripe payments, adding price from another model into payment method - ruby-on-rails

Question

I have added Stripe payment to my app to handle registration payments for events, the form is on the event show page so the method is in the events controller but I have created a registration model. My issue is trying to get the price of the event into the save_with_payment method inside the registration model(total_price).
Any ideas? I have tried attr_accessible :price but with no luck.
Event Controller
def show
#event = Event.where(:slug => params[:slug]).first
#registration = Registration.new
end
def payment
#registration = Registration.new(params[:registration])
if #registration.save_with_payment
RegistrationMailer.admin(#registration, #event).deliver
RegistrationMailer.delegate(#registration, #event).deliver
redirect_to root_path
flash[:success] = "Thank you for registering for <% #event.title %>"
else
redirect_to root_path
flash[:error] = "We're sorry, something went wrong"
end
end
Registration Model
def save_with_payment
if valid?
charge = Stripe::Charge.create({
amount: total_price, ##I can declare a integer here instead of a method and it works
currency: "gbp",
card: stripe_card_token,
description: email })
save
end
rescue Stripe::CardError => e
end
def total_price
#event.price = price
price
end
Routes
match 'registration' => 'events#show', :via => :get
match 'registration' => 'events#payment', :via => :post
View
<%= simple_form_for [#registration], :method => :post, :url => registration_path do |f| %>
<%= f.input :first_name %>
<%= f.input :last_name %>
<%= f.input :email %>
<%= f.input :job_title %>
<%= f.input :company %>
<%= f.input :stripe_card_token, as: :hidden %>
<div class="input card_number">
<label for="card_number">Card number</label>
<%= text_field_tag :card_number %>
</div>
<div class="input card_cvc">
<label for="card_code">Security code (CVC)</label>
<%= text_field_tag :card_cvc %>
</div>
<div class="input card_dates">
<label>Card expiration date</label>
<%= select_month nil, { add_month_number: true }, { id: "card_month"} %>
<%= select_year nil, { add_year: Date.today.year, end_year: Date.today.year + 15 }, { id: "card_year"} %>
</div>
<%= f.button :submit, "Register", class: "button" %>

Answer 1

If I got everything right, here:
def show
#event = Event.where(:slug => params[:slug]).first
#registration = Registration.new
end
is controller action with view, containing form.
Registration should belong to event, I suppose, through :has_one
Then your registration model needs event_id integer column. As you declared #event in show, append you registration form with
<%= f.input :event_id, as: :hidden, value: #event.id %>
After that you can find #event in payment method by:
#event=Event.find(params[:registration][params[:event_id]].to_i)
This is basic example, I don't actually know, what is event in your app, may be there is better attribute which you can pass.
After that you can pass #event.price as argument to model method:
def save_with_payment(total_price)
if valid?
charge = Stripe::Charge.create({
amount: total_price,
#other code