Rails how assign created_at in a model and / or model callback to an attribute

Question

I am building an e-commerce app. I want to assign created_at to an attribute.

Stale Product inventory is 'sent' / 'submitted' to the SaleController, creating a product on sale.

1. I am trying to assign the time created_at to sale_start_time - an attribute of the model Sale - which I can later use to trigger mark-downs, for example, @sale_start_time+5day . In the Sale model:

    def sale_start_time
        @sale.created_at
    end
   
   

That does not work, nor does @sale_start_time = @sale.created_at -- even though in a view, for example sales#show, @sale.created_at returns the created_at time.

2. I also tried placing it in a Sale model after commit (although I can't determine if two attributes can be changed in a single after commit). Product does toggle product_on_sale: false to product_on_sale: true (which, practically speaking, removes it from product inventory). The Sale update of the attribute doesn't work. It 'raises' 'id'={:id=>nil} I'd user Sale.find_by(@product_id)... however, product_id may not equal sale_id.

   def update_status
      Product.find_by(@product_id).toggle!(:product_on_sale)
      Sale.find(id: @id).update(sale_start_time: @sale.created_at)
   end
   

Thank you in advance for your help.

Answer 1

If I understood your question correctly, you can assign it in a after_create callback.

In the Sale model add this:

class Sale
  # other stuff
  after_create :assign_start_time  

  # other methods

  private

  def assign_start_time
    self.sale_start_time = created_at
    self.save!
  end
end

Edit by OP: This works IF the controller method def create defines sale as @sale = Sale.create(sale_params) 'create' sets the sale id. I was using @sale = Sale.new(sale_params) which does not set the sale id until the transaction is committed.