Help me about Bcrypt-ruby

I'm create a login form using Bcrypt-ruby but have error:

uninitialized constant User::BCrypt
I had setup Bcrypt-ruby in Gemfile

  gem "bcrypt-ruby", :require => "bcrypt"

and restart,rake db:migrate but not run.I had run bundle:install,bundle:
update and see Bcrypt had installed.
i'm afraid that i use gem 'rails', '3.2.1' in Gemfile
Could you help me solve this problem...Thanks

I'm create a login form using Bcrypt-ruby but have error:

uninitialized constant User::BCrypt

What is User::BCrypt supposed to be? Where/how did you define it? (It
appears you didn't, actually. Show some code so we have a half a
chance of helping you.)