app/models/user.rb
class User
include Mongoid::Document
include ActiveModel::SecurePassword
attr_accessible :first_name, :last_name, :email, :password, :password_confirmation
field :first_name, :type => String
field :last_name, :type => String
field :email, :type => String
field :password_digest, :type => String
embeds_many :samples
has_secure_password
email_regex = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
validates :first_name, :presence => true
validates :last_name, :presence => true
validates :email, :presence => true, uniqueness: { case_sensitive: false }, format: { with: email_regex }
validates :password, :presence => true, :confirmation => true
end