Building children models without using accepts_nested_attributes_for

product_form.rb

class ProductForm
  include ActiveModel::Model
  include ActiveModel::Attributes

  attr_accessor :images

  attribute :deliverable_days, :integer
  attribute :detail, :string
  attribute :name, :string
  attribute :price, :integer
  attribute :shipping_fee_charges_on, :integer
  attribute :shipping_from, :integer
  attribute :status, :integer

  def images_attributes=(attributes)
    @images ||= []
    attributes.each do |i, image_params|
      @images.push(ProductImage.new(image_params))
    end
  end
  
  def save
   # implement as you like 
   # @product_form = ProductForm.create(attributes)
   # @product_form.children.create
  end
end

# In some controllers
# def new
#   @product_form = ProductForm.new(images: [Image.new])
# end

# def create
#   @product_form = ProductForm.new(product_form_params)
#   @product_form.save
# end