processing by create instead of update - ruby-on-rails

Question

when I attempt to run my code, I got the error above.
I try to add specific attributes to my products, but every time I try to add them to my product, a new one is created instead of just edit the old.
Here is the result :
Started POST "/my_products" for 127.0.0.1 at 2016-01-03 16:33:46 +0100
[localhost] [127.0.0.1] [a6533ae8-475f-4e] Processing by MyProductsController#create as JS
[localhost] [127.0.0.1] [a6533ae8-475f-4e] Parameters: {"utf8"=>"✓", "my_product"=>{"size_name"=>"Gros oeuf", "size_img"=>"big-egg.png", "size_price"=>"40"}, "commit"=>"Choisir"}
[localhost] [127.0.0.1] [a6533ae8-475f-4e] (0.2ms) BEGIN
[localhost] [127.0.0.1] [a6533ae8-475f-4e] SQL (0.3ms) INSERT INTO `my_products` (`size_name`, `size_price`, `size_img`, `created_at`, `updated_at`) VALUES ('Gros oeuf', '40', 'big-egg.png', '2016-01-03 15:33:46', '2016-01-03 15:33:46')
[localhost] [127.0.0.1] [a6533ae8-475f-4e] (2.0ms) COMMIT
My application_controller.rb :
def current_product
if !session[:my_product_id].nil?
MyProduct.find(session[:my_product_id])
else
MyProduct.new
end
end
My Products_controller :
def base
#myproduct = current_product
#size = Size.all
#chocolate = MyProductItem.where(item_category_id: 1)
end
def create
#myproduct = current_product
if #myproduct.update(my_product_params)
redirect_to(:back)
else
render 'new'
end
end
My base.html.erb :
<% #size.each do |size| %>
<div class="Box" >
<p><%= size.name %></p>
<p><%= image_tag size.image, style: 'width:7em;height:auto;' %></p>
<p><%= number_to_currency size.price %></p>
<p><%= size.description.try(:html_safe) %></p>
<%= form_for #myproduct, remote: true do |f| %>
<%= f.hidden_field :size_name, value: size.name %>
<%= f.hidden_field :size_img, value: size.image %>
<%= f.hidden_field :size_price, value: size.price %>
<%= f.submit "Choisir", class: "addtocart", :id => "#orders" %>
<% end %>
</div>
<% end %>
My models :
class MyProduct < ActiveRecord::Base
attr_accessible :name, :slug, :price, :image, :my_product_item_id, :user_id, :size_name, :size_img, :size_price
has_many :elements, dependent: :destroy
has_one :size, dependent: :destroy
belongs_to :user
belongs_to :order
class Size < ActiveRecord::Base
attr_accessible :name, :price, :weight, :image, :description, :object_size
belongs_to :my_product
end
Any idea ?

Answer 1

Add field with proper :my_product_id value into the form:
<%= hidden_field_tag(:my_product_id, #my_product.id) if #my_product %>
If you invoke base action with GET request without parameters new object will be created, for update you must pass to this action parameter my_product_id=value (value is an id of updated product).