create_job_users.rb

class CreateJobsUsers < ActiveRecord::Migration
  def change
    create_table :jobs_users, :id => false do |t|
      t.integer :job_id
      t.integer :user_id

      t.timestamps
    end
  end
end

index.html.erb

<h2>Lediga jobb</h2>
<table width="700">
	<tr align="left">
		<th>Datum </th>
		<th>Arbetsbeskrivning</th>
		<th>Ort</th>
    <th></th>
	</tr>
	<% @jobs.each do |job| %>
	<tr>
	  <td><%= job.updated_at.strftime("%d/%m/%Y") %></td>
	  <td><%= job.name %></td>
	  <td>Stockholm</td>
    <td>
      <% if current_user %>
        <%= link_to "Apply job", add_job_path(job.id), :method => :put %>
      <% end %>
    </td>
	</tr>
<% end %>
</table>

<br />

job.rb

class Job < ActiveRecord::Base
  has_many :users, :through => :jobs_users
end

jobs_controller.rb

class JobsController < InheritedResources::Base
  before_filter :authenticate_user!, :except => [:index, :show]

  def add_job
    user = current_user
    if user.update_attributes(:user_id => current_user.id)
      redirect_to jobs_path, :notice => "You have now applied for this job."
    end
  end
end

routes.rb

Yc::Application.routes.draw do
  resources :jobs
  match "add_job/:id" => "jobs#add_job", :as => "add_job", :via => :put

  ActiveAdmin.routes(self)

  devise_for :admin_users, ActiveAdmin::Devise.config

  devise_for :users

root :to => "home#index"

end

schema.rb

ActiveRecord::Schema.define(:version => 20111102205359) do
  create_table "jobs", :force => true do |t|
    t.string   "name"
    t.string   "title"
    t.text     "content"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "user_id"
  end

  create_table "jobs_users", :id => false, :force => true do |t|
    t.integer  "job_id"
    t.integer  "user_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "users", :force => true do |t|
    t.string   "email",                                 :default => "", :null => false
    t.string   "encrypted_password",     :limit => 128, :default => "", :null => false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",                         :default => 0
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "fname"
    t.string   "lname"
    t.string   "bday",                   :limit => nil
    t.string   "address"
    t.string   "areacode"
    t.string   "city"
    t.string   "education"
    t.text     "info"
    t.string   "looking_for"
    t.string   "tele"
    t.string   "cv_file_name"
    t.string   "cv_content_type"
    t.integer  "cv_file_size"
    t.datetime "cv_updated_at"
    t.string   "photo_file_name"
    t.string   "photo_content_type"
    t.integer  "photo_file_size"
    t.datetime "photo_updated_at"
    t.integer  "job_id"
  end

end

user.rb

# encoding: UTF-8
class User < ActiveRecord::Base
  has_many :jobs, :through => :jobs_users
  
  devise :database_authenticatable, :registerable, :recoverable, :trackable, :validatable

  attr_accessible :email, :password, 
    :password_confirmation, 
    :remember_me, 
    :fname, 
    :lname, 
    :bday, 
    :address, 
    :areacode, 
    :city, 
    :education, 
    :info, 
    :looking_for, 
    :tele,
    :cv,
    :cv_file_name, 
    :cv_content_type,
    :cv_file_size,
    :cv_updated_at

  has_attached_file :cv

  validates_attachment_size :cv, :less_than => 2.megabytes
end