accounts_controller.rb

# route.rb has:
# resources :user do
#   resources :accounts do
# end

class AccountsController < ApplicationController
  before_filter :retrieve_user

  respond_to :html, :json
  # GET /accounts
  # GET /accounts.json
  def index
    @accounts = Account.all
    @accounts = @user.accounts if @user
    
    respond_with @accounts
  end

  protected
  def retrieve_user
    @user = User.find params[:user_id]
  end
end