Rails - Add more nested attributes dynamically

Question

This seems like a pretty trivial problem but i am not able to solve this. I have two tables invoices and invoice_items. In invoice model:

accepts_nested_attributes_for :invoice_items, allow_destroy: true, reject_if: :all_blank 

Now in a method based on some conditions i want to add more invoice items dynamically. In before_save callback i am doing something like this:

def process_amounts if condition_holds self.invoice_items_attributes << {key_1: value_1, key_2: value_2} # Pseudo code. end end 

But this piece of code raises errors. Seems like only setter is available for nested_attributes.

NoMethodError Exception: undefined method `invoice_items_attributes' for # Invoice:0x007fd4de84a7a0

I also tried one another approach which results in weird behavior:

def process_amounts if condition_holds self.invoice_items_attributes = invoice_items.map(&:attributes) + [{key_1: value_1, key_2: value_2}] # Pseudo code. end end 

The above piece of code results in 3 items! It doesn't reassign the invoice_items_attributes.

So how to fix this problem?

Answer 1

Try this

 if condition_holds self.invoice_items << InvoiceItem.new(key_1: value_1, key_2: value_2) end 

I'm assuming InvoiceItem is the model name for invoice_items.

Answer 2

invoice_item_attributes is only available in params(Controller). You can do this in model invoice in before_save callback like this.

before_save :process_amounts

def process_amounts if condition_holds self.invoice_items.build([{key: value, key2: value2},{key: value, key2: value2}]) end