Transmit params with form_tag - ruby-on-rails

Question

In my views I have a form and trying to update quantity for an order line:
<div class="quantity">Quantity</br>
<%= form_tag(order_line_path(line.id), method: "patch") do %>
<%= number_field_tag 'qty', '1', within: 1...line.book.stock %>
<%= submit_tag "Update", class: "btn btn-primary" %>
<% end %>
</div>
The instance variable in the rest of my view is a collection of order lines, so I cannot use it.
Then I have in my controller the update method:
def update
#order = current_order
#order_line = #order.order_lines.find(params[:id])
#order_line.update_attributes(order_line_params)
end
And my strong params definition:
def order_line_params
params.require(:order_line).permit(:qty)
end
I get this error :
param is missing or the value is empty: order_line
Could someone please have a look?
Thanks!

Answer 1

The reason you are getting param is missing or the value is empty: order_line is that you are using form_tag which gives a "flat" params hash.
However this is easily avoidable if you just use form_with/form_for.
# routes.rb
resources :orders do
resources :line_items, shallow: true
end
# app/views/order_items/edit.html.erb
# use `form_with(model: #order_item)` in Rails 5
<%= form_for(#order_item) do |f| %>
<%= f.label :qty, within: 1...f.object.book.stock %>
<%= f.number_field :qty, %>
<%= f.submit %>
<% end %>
class OrderItemsController < ApplicationController
before_action :set_order_item, only: [:show, :edit, :update, :destroy]
# ...
# GET /order_items/:id/edit
def edit
end
# PATCH /order_items/:id
def update
if #order_item.update(order_item_params)
redirect_to #order_item, notice: 'Line updated'
else
render :edit
end
end
private
def set_order_item
#order_item = OrderItem.find(params[:id])
end
def order_item_params
params.require(:order_item).permit(:qty)
end
end
But what you're really looking for unless you are doing the update/creation of nested items with AJAX is most likely a combination of accepts_nested_attributes and fields_for which will let the user mass edit the line items:
class Order < ApplicationRecord
accepts_nested_attributes_for :order_items
end
<%= form_for(#order) do |f| %>
<%= fields_for(:order_items) do |oif| %>
<%= f.label :qty, within: 1...f.object.book.stock %>
<%= f.number_field :qty, %>
<% end %>
<%= f.submit %>
<% end %>
class OrdersController < ApplicationController
# PATCH /orders/:id
def update
if #order.update(order_params)
redirect_to #order, notice: 'Order updated.'
else
render :new
end
end
private
def order_params
params.require(:order).permit(order_items_attributes: [:qty])
end
end