ActiveModel nested attributes with validation

non_persistent_nested_records_example.rb

class Order
  include ActiveModel::Model
  
  attr_accessor :order_lines, :name

  def initialize(*params)
    self.order_lines = []
    super
  end

  def order_lines_attributes=(attributes)
    attributes.each do |i, order_lines_params|
      @order_lines.push(OrderLine.new(order_lines_params))
    end
  end
  
  def valid?
    parent_valid = super
    children_valid = order_lines.map(&:valid?).all?
    order_lines.each do |ol| 
      ol.errors.each do |attribute, error|
        errors.add(:order_lines_attributes, error)
      end
    end
    errors[:order_lines_attributes].uniq!
    parent_valid && children_valid
  end
end

class OrderLine
  include ActiveModel::Model
  
  attr_accessor :line_number, :item_number # etc
 
end