ruby on rails - Update Cart's Quantity if same Product added -

i new ror. building e-commerce site. in shopping cart if try add products added if product not added before. want if user add same product quantity should incremented.

here add_to_cart method in carts_controller.rb in advance.

def add_to_cart   @cart = cart.find_by_product_id_and_user_id( params[:product_id], current_user.id)    if @cart.nil?     @cart = cart.create(:user_id => current_user.id, :product_id => params[:product_id], :quantity => '1')   else      @cart.update(:quantity +=> '1')   end     redirect_to view_cart_path end 

your schema seems strange: why carts have product id? suggests cart "belongs_to" product, wrong. i'd have expected each user have single cart, , cart have list of products via join table. this:

class user    has_one :cart end  #user_id class cart   belongs_to :user   has_many :cart_products   has_many :products, :through => :cart_products end  #cart_id, product_id, :quantity class cartproduct   belongs_to :cart   belongs_to :product end  #various fields specific product class product   has_many :cart_products   has_many :carts, :through => :cart_products end 

if schema, handle quantity updating so:

#in cart class def add_product(product)   if cart_product = self.cart_products.find_by_product_id(product.id)     cart_product.quantity += 1     cart_product.save     cart_product   else     self.cart_products.create(:product_id => product.id, :quantity => 1)   end end