updating cart via button - ruby-on-rails

Question

I'm trying to be on that page right before the checkout, where you can modify the quantity and update all the prices accordingly. Now my "Update" button, updates 'something' but it's not what i'm trying to achieve, it sends me on a line_items show page that i don't even want to have (i'm keeping it for now to avoid the missing template error). The rails documentation isn't helping me ... well anyway, the code is this
<ul>
<% #cart.line_items.each do |item| %>
<%= form_for(item) do |f| %>
<li><%= f.number_field :quantity, :value => item.quantity %> x <%= item.product.name %>
<%= item.total_price %> </li>
<% end %>
<%= submit_tag "Update" %>
<% end %>
<br><strong>Total Price:</strong> <%= #cart.total_price %>
</ul>
<%= button_to "Checkout", new_order_path, method: :get, data: { confirm: "Are you sure?" } %>
<%= button_to 'Empty cart', #cart, method: :delete, data: { confirm: 'Are you sure?' } %>
<%= link_to 'Back', categories_path %>
Thank you !
edited
class LineItemsController < ApplicationController
include CurrentCart
before_action :set_cart, only: [:create, :update, :destroy]
before_action :set_line_item, only: [:show, :edit, :update, :destroy]
# GET /line_items
# GET /line_items.json
def index
#line_items = LineItem.all
end
# GET /line_items/1
# GET /line_items/1.json
def show
end
# GET /line_items/new
def new
#line_item = LineItem.new
end
# GET /line_items/1/edit
def edit
end
# POST /line_items
# POST /line_items.json
def create
product = Product.find(params[:product_id])
#line_item = #cart.add_product(product.id)
respond_to do |format|
if #line_item.save
format.html { redirect_to #line_item.cart, notice: 'Line item was successfully created.' }
format.json { render :show, status: :created, location: #line_item }
else
format.html { render :new }
format.json { render json: #line_item.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /line_items/1
# PATCH/PUT /line_items/1.json
def update
respond_to do |format|
if #line_item.update(line_item_params)
format.html { redirect_to #cart, notice: 'Line item was successfully updated.' }
format.json { render :show, status: :ok, location: #line_item }
else
format.html { render :edit }
format.json { render json: #line_item.errors, status: :unprocessable_entity }
end
end
end
# DELETE /line_items/1
# DELETE /line_items/1.json
def destroy
#line_item.destroy
respond_to do |format|
format.html { redirect_to line_items_url, notice: 'Line item was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_line_item
#line_item = LineItem.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def line_item_params
params.require(:line_item).permit(:product_id, :cart_id, :order_id)
end
end

Answer 1

Just do redirect after you update an item. And provide correct line_item_update_params method that permites quantity param. Your controller should look like that:
class ItemsController < ApplicationController
def update
item = Item.find(params[:id])
item.update(line_item_update_params)
redirect_to :back # this is the key line of code
end
...
private
# it is used for creating
def line_item_params
params.require(:line_item).permit(:product_id, :cart_id, :order_id)
end
# it is used for updating
def line_item_update_params
params.require(:line_item).permit(:quantity)
end
...
end