Decrease/Increase from member variable in rails via form

I have two classes A and B
B belongs to A and A has many Bs with resources configured as:

  resources :as do
    resources :bs
  end

B has a member variable amount which I want to be able to decrease and increase from the front end using a form, in this case, it cannot be the edit form.

Can I do this at all? and can I do where the form opens in a pop up on following a link to?

The function I imagine for increase is something like this:

def increase()
   @b = b.find(params[:id])
   @b.amount = @b.amount + params[:amount]
   @.update
end

I Just cannot wrap my head around how to do it.

You can create a custom route. Many diff non-resourceful routes in the Rails Guides to check out.

One way is with the following:

• using put because this is an update request
• using on: :member to capture the bs params[:id] on the route

# routes.rb

resources :as do
  resources :bs do
    put 'increase_amount', on: :member
    put 'decrease_amount', on: :member
  end
end

# bs controller

def increase_amount()
   @b = B.find(params[:id])
   amount = @b.amount + params[:amount]
   if @b.update(amount: amount)
     ...
   else
     ...
   end
end

def decrease_amount()
   @b = B.find(params[:id])
   amount = @b.amount - params[:amount]
   if @b.update(amount: amount)
     ...
   else
     ...
   end
end

# haven't verified this is the correct route name, confirm using rake routes
<%= form_tag(increase_amount_a_bs_path(@a, @b), method: :put) do %>
  <%= label_tag(:amount, "Increase Amount:") %>
  <%= number_field_tag(:amount) %>
  <%= submit_tag("Update Amount") %>
<% end %>

<%= form_tag(decrease_amount_a_bs_path(@a, @b), method: :put) do %>
  <%= label_tag(:amount, "Decrease Amount:") %>
  <%= number_field_tag(:amount) %>
  <%= submit_tag("Update Amount") %>
<% end %>

As for the popup, I'm not sure what frontend library in your tech stack but Bootstrap comes to mind as an option, modal