RoR permitting non model parameter

Question

I'm having a hard time trying to understand how to permit non model parameters.

I've read:

• Rails Strong Parameters: How to accept both model and non-model attributes?
• Rails 4 Strong parameters : permit all attributes?
• Strong Parameters

So, for a "normal" situation - let's say that I have a model Foo which has just one attribute bar:

# foo.rb
class Foo < ActiveRecord::Base
  # bar, which is a integer
end

# views/foos/new.html.erb
<%= form_for @foo do |f| %>
    <%= f.number_field :bar %>
    <%= f.submit %>
<% end %>

#foos_controller.rb
def create
    @foo = Foo.new(foo_params)
    # ...
end

#...

private

def foo_params
    params.require(:foo).permit(:bar)
end

So, when I submit the form, the Foo will be created.

---

However, what if the bar attribute has some logic behind it that combines some non model parameters? Let's say that bar is the sum of two parameters (bar = bar_1 + bar_2). Then the view and controller looks like:

# views/foos/new.html.erb
<%= form_for @foo do |f| %>
    <%= f.number_field :bar_1 %>
    <%= f.number_field :bar_2 %>
    <%= f.submit %>
<% end %>

#foos_controller.rb
def create
  bar_1 = params[:foo][:bar_1]
  bar_2 = params[:foo][:bar_2]

  if bar_1.present? && bar_2.present?
    @foo = Foo.new
    @foo.bar = bar_1.to_i + bar_2.to_i

    if @foo.save
      # redirect with success message
    else
      # render :new
    end
  else
    # not present
  end
end

So the question is, do I also need to permit the bar_1 and bar_2 parameters? If I do, how do I permit them?

Answer 1

If you want to access those two non-model parameter, you have to bind it with model by below code on your Foo model

attr_accessor :bar_1, :bar_2

No need to permit it in

def foo_params
   params.require(:foo).permit(:bar)
end

Note: Make sure you remove it from your params, It will not raise any error, but give you a warning on rails console like Unpermitted parameters: bar_1, bar_2