Creating new registration and new order at the same time - ruby-on-rails

Question

I'm trying to add an event registration to a current or new order. Question at the end of the post.
Event model: Contains the basic event information like title, date, description. This event model has many event options.
Event Option: Contains a description and a price. This event option has many registrations.
Registration: Allows the user to register and it takes the price from the event option price. This registration belong to an event option and to the order model.
Order: Calculates the total of the order based on the sum of all the registrations associated with it.
Creating a new registration:
In the event option show page, I have a form that creates a new registration using remote: true.
Here's the form:
<%= form_for(#registration, remote: true) do |f| %>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :lastname %><br>
<%= f.text_field :lastname %>
</div>
<div class="field">
<%= f.label :event_option_id %><br>
<%= f.text_field :event_option_id, value: #event_option.id %>
</div>
<div class="field">
<%= f.label :order_item_id %><br>
<%= f.text_field :order_item_id%>
</div>
<div class="field">
<%= f.label :price %><br>
<%= f.text_field :price, value: #event_option.price%>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
When the form is submitted, it creates the event and also creates a new order if the order does not exist. To create the new order I have this helper method in the application controller:
def current_order
if !session[:order_id].nil?
Order.find(session[:order_id])
else
Order.new
end
end
Here's the create method in the registrations controller:
def create
#order = current_order
#registration = Registration.new(registration_params)
#order_id = current_order.id
respond_to do |format|
if #registration.save
format.html { redirect_to #registration, notice: 'Registration was successfully created.' }
format.json { render :show, status: :created, location: #registration }
format.js {}
#order.save
session[:order_id] = #order.id
else
format.html { render :new }
format.json { render json: #registration.errors, status: :unprocessable_entity }
end
end
end
The problem is that I'm not able add the registration to the order. I'm guessing that this is happening because the registration is created before the order. The last two line of the if #registration.save in the respond_to block are saving the order. How can I add the registration to the order? Can both, the new registration and new order be created at the same time?

Answer 1

A simple way to get around this is to assign the registration to the order before saving the order...
#order.registrations << #registration
#order.save
Alternatively you could create the association at the time you're creating the #registration record.
Instead of...
#registration = Registration.new(registration_params)
do....
#registration = #order.registrations.build(registration_params)