Rails-在保存之前迭代has_many关联的嵌套属性

Question

I have a model and a has_many association.

Say,

class Invoice < ActiveRecord::Base
  has_many :lines, class_name: 'InvoiceLine', inverse_of: :invoice, dependent: :destroy
  accepts_nested_attributes_for :lines, reject_if: :invalid_line, allow_destroy: true
end

Is it possible for me to iterate through the lines before it is saved (especially during an update), either in InvoicesController or in Invoice model?

When I iterate on the existing record during an update, I get old lines, not the updated lines from the view.

Currently I am doing the following in the controller. I am not quite happy with this.

total = params["invoice"]["lines_attributes"].
          map{|k,v| [v["amount"], v["_destroy"]]}.
          select{|x| x[1] == "false"}.
          map{|x| x[0].to_f}.
          inject {|total, amount| total + amount}

Answer 1

You can use assign_attributes and marked_for_destruction? as:

@invoice.assign_attributes(params[:invoice])
total = @invoice.lines.select(&:marked_for_destruction?).map(&:amount).sum
@invoice.save #save all on db