image.rb

require 'securerandom'
class Image < ActiveRecord::Base
  validates :title, presence: true
  validates :image, presence: true
  extend FriendlyId
  friendly_id :random_id

  belongs_to :user
  mount_uploader :image, ImageUploader

  before_save :random_string

 

  def random_string
    self.random_id = SecureRandom.urlsafe_base64(6)
    self.user_id = current_user.id
  end
end

images_controller.rb

class ImagesController < ApplicationController
  def new
    @image = Image.new
  end

  def create
    @image = Image.new(image_params)
    if @image.save
      redirect_to image_path(@image.id)
    else
      redirect_to 'new'
    end
  end

  def show
    @image = Image.friendly.find(params[:id])
  end
  
  private
    def image_params
      params.require(:image).permit(:user_id, :title, :image, :random_id)
    end
end

new.html.erb

<% if @image.errors.any? %>
  <div id='error_explanation'>
    <h2><%= pluralize(@image.errors.count, "error") %></h2>
    <ul>
      <% @image.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
    </ul>
  </div> 
<% end %> 
<%= form_for @image, :html => {:multipart => true} do |f| %>
  <%= f.label :title, :class =>'textfield' %><br />
  <%= f.text_field :title, :class =>'textfield' %><br />
  <%= f.file_field :image %><br />
  <!--<button id='custom_button'>Browse</button>-->
  <%= f.submit "Upload" %>
<% end %>