validation and accepts_nested_attributes_for - ruby-on-rails

Question

i have two models :
class Article < ActiveRecord::Base
belongs_to :league
has_many :photos, :dependent => :destroy
attr_accessible :content, :lead, :title, :title_slug,
:created_at, :updated_at,
:league_id, :photos_attributes
accepts_nested_attributes_for :photos
validates :content, :league, :presence => true
validates :lead , :length => {maximum: 1000}, :presence => true
validates :title ,:length => {maximum: 200}, :presence => true
validates_associated :photos
and
class Photo < ActiveRecord::Base
belongs_to :article
attr_accessible :photo
validates :photo, presence: true
has_attached_file :photo , :styles => { :medium => '440x312#', :small => '209x105!'}
end
My ArticlesController is
...
def new
#article = Article.new
#article.photos.build
end
def create
#article = Article.new(params[:article])
if #article.save
redirect_to([:admin,#article])
else
render 'new'
end
end
...
form view is :
= form_for([:admin,#article] , :html => {:multipart => true}) do |f|
- if #article.errors.any?
= render 'errors'
= f.fields_for :photos do |builder|
= builder.label :photo
= builder.file_field :photo
...
i have some question about it :
1) I dont want to save an article without empty photo but now when i dont choose a file my article saves.
2) When i have some errors on article's fields and render 'new' ,my photo field dissapear , what is the rails way to resolve it.
3) in the future i want to add another model: photo_type and assosciate it with photo. Each article will have two photo fields , each with own type (for example: small , big) . I wonder how to render that fields and what can i do to save article with two photos with different types.

Answer 1

Answer for 1: Use validates_associated :photos. Documentation
Answer for 2: I guess that is an file attachment field. For that, this is generally done by setting up a hidden cache field and by using some callbacks. MountUploader uses the same principle.
Answer for 3: Little skeptical, but I guess something will work along this way:
In your Article model, have two associations with Photo as:
has_one :small_photo, :class_name => "Photo"
has_one :big_photo, :class_name => "Photo"
This will enable you to have two sub-form fields present for both types while opening up the form for Article.
Hope it helps. Do comment if last one can work for you in this way. It looks like the good deal to me :)