Schema

create_table "users" do |t|
  t.string "name"
  t.json   "avatar"
  t.json   "photos"
end 

Model

class User < ActiveRecord::Base
  has_one_attache   :avatar
  has_many_attaches :photos
  validates_presence_of :name
end 

Form

null
= f.file_field :avatar, f.object.avatar_options('190x190#', placeholder: image_path('placeholder.png')) 
null
= f.file_field :photos, f.object.photos_options('190x75#', placeholder: image_path('placeholder.png')) 
or Cancel