Login with username or email in Rails 3 without using device gem

Please help me to login with username or email using Rails 3. I have two models: Admin and User. Admin can only login through email and user can only login through username. I need both login process and i don't want to use device gem . Please check my below codes and help me to resolve this issue.

views/admins/index.html.erb

<div id="login">
  <div id="triangle"></div>
  <h1>Log in</h1>
  <%= form_for :admin,:url => {:action => "login" ,:controller => "sessions" } do |f| %>
  <%= f.text_field :login,placeholder:"Enter your email or username" %>
  <%= f.password_field :password,placeholder:"Enter your password" %>
  <%= f.submit "Log in" %>
  <% end %>
  <% if @admin.try(:errors).try(:any?) %>
    <div id="error_explanation">
    <h2><%= pluralize(@admin.errors.count, "error") %> prohibited this post from being saved:</h2>

    <ul>
    <% @admin.errors.full_messages.each do |msg| %>
   <li><%= msg %></li>
   <% end %>
   </ul>
  </div>
<% end %>
</div>

sessions/sessions_contrtoller.rb

class SessionsController < ApplicationController
    def login
        @admin=Admin.authenticate(params[:admin][:email], params[:admin][:password])
        if @admin
            session[:user_id]=@admin.id
            cookies.signed[:user_id]=@admin.id
            flash[:notice]="Login Successfull"
            flash[:color]="valid"
            redirect_to :action => 'index', :controller => "homes"
        else
            flash[:notice]="Login failed"
            flash[:color]="invalid"
            render 'admins/index'
        end
    end
    def removeadmin
        session[:user_id] = nil
        cookies.delete :user_id
        flash[:notice]="user logged out successfully"
        flash[:color]="valid"
        redirect_to :action => 'index', :controller => 'admins'
    end
end

model/admin.rb

class Admin < ActiveRecord::Base
  attr_accessible :email, :name, :password, :phoneno
  attr_accessor :login
  EMAIL_REGEX = /\A[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\z/i
 validates :email, :presence => true, :uniqueness => true, :format => EMAIL_REGEX
 validates_length_of :password, :in => 6..20, :on => :create
 has_many :user
 def self.authenticate(email, password)
    admin = find_by_email(email)
    if admin && admin.password==password
      admin
    else
      nil
    end
  end
end

model/user.rb

class User < ActiveRecord::Base
  belongs_to :admin
  attr_accessible :email, :password_hash, :password_salt, :phoneno, :user_name,:password, :password_confirmation
  attr_accessor :password
  before_save :encrypt_password
  validates_confirmation_of :password
  validates_presence_of :password, :on => :create
  validates_presence_of :email
  validates_uniqueness_of :email
  def encrypt_password
    if password.present?
      self.password_salt = BCrypt::Engine.generate_salt
      self.password_hash = BCrypt::Engine.hash_secret(password, password_salt)
    end
  end
end

I found in many post where answer was about device gem.Please help for this scenario.