How to save uploaded files to your database in Rails

20101004063749_create_photos.rb

# db/migrate/20101004063749_create_photos.rb

class CreatePhotos < ActiveRecord::Migration
  def self.up
    create_table :photos do |t|
      t.string :name,         :null => false
      t.binary :data,         :null => false
      t.string :filename
      t.string :mime_type
      t.timestamps
    end
  end

  def self.down
    drop_table :photos
  end
end

new.html.erb

# app/views/photos/new.html.erb

<%= form_for(@photo, :html => {:multipart => true}) do |f| %>
  <div class="field">
    <%= f.label :name %>
    <%= f.text_field :name %>
  </div>
  <div class="field">
    <%= f.label :data %>
    <%= f.file_field :data %>
  </div>
  <div class="actions">
    <%= f.submit "Upload" %>
  </div>
<% end %>

photos_controller.rb

# app/controllers/photos_controller.rb

class PhotosController < ApplicationController
  def index
    @photos = Photo.all
  end

  def show
    @photo = Photo.find(params[:id])
  end
  
  def new
    @photo = Photo.new
  end

  def create
    
    # build a photo and pass it into a block to set other attributes
    @photo = Photo.new(params[:photo]) do |t|
      if params[:photo][:data]
        t.data      = params[:photo][:data].read
        t.filename  = params[:photo][:data].original_filename
        t.mime_type = params[:photo][:data].content_type
      end
    end
    
    # normal save
    if @photo.save
      redirect_to(@photo, :notice => 'Photo was successfully created.')
    else
      render :action => "new"
    end
  end
  
  def destroy
    @photo = Photo.find(params[:id])
    @photo.destroy
    redirect_to(photos_url)
  end
end

photos_controller_update.rb

# app/controllers/photos_controller.rb

class PhotosController < ApplicationController
  
  # ...
  
  def serve
    @photo = Photo.find(params[:id])
    send_data(@photo.data, :type => @photo.mime_type, :filename => "#{@photo.name}.jpg", :disposition => "inline")
  end

end

routes.rb

# rails3
resources :photos do
  get "serve", :on => :member
end

# rails 2.x
resources :photos, :member => {:serve => :get}

usage.html.erb

<%= image_tag serve_photo_path(@photo) %>

Great tutorial, thanks. I'm having an issue when the user wants to edit the file uploaded. I tried like below in update:
def update
if params[:record_revision][:filename]
@record_revision = RecordRevision.find(params[:id]) do |t|
t.file_contents = params[:record_revision][:filename].read
t.filename = params[:record_revision][:filename].original_filename
t.content_type = params[:record_revision][:filename].content_type
end
end
but still have "... undefined method `name' for nil:NilClass ..."
could you help on that?
thanks