我正在线上的rails教程书，当我转到http：// localhost：3000 /时，我收到以下错误消息
“未初始化的常量ApplicationRecord”
它给了我以下代码突出显示第一行。
class User < ApplicationRecord attr_accessor :remember_token before_save { self.email = email.downcase } validates :name, presence: true, length: { maximum: 50 } VALID_EMAIL_REGEX = /\A[\w+\-.]+@[az\d\-.]+\.[az]+\z/i validates :email, presence: true, length: { maximum: 255 }, 这是我的application.html.erb文件：
和我的user.rb文件：
class User < ApplicationRecord attr_accessor :remember_token before_save { self.email = email.downcase } validates :name, presence: true, length: { maximum: 50 } VALID_EMAIL_REGEX = /\A[\w+\-.]+@[az\d\-.]+\.[az]+\z/i validates :email, presence: true, length: { maximum: 255 }, format: { with: VALID_EMAIL_REGEX }, uniqueness: { case_sensitive: false } has_secure_password validates :password, presence: true, length: { minimum: 6 } # Returns the hash digest of the given string. def User.digest(string) cost = ActiveModel::SecurePassword.min_cost ? BCrypt::Engine::MIN_COST : BCrypt::Engine.cost BCrypt::Password.create(string, cost: cost) end # Returns a random token. def User.new_token SecureRandom.urlsafe_base64 end # Remembers a user in the database for use in persistent sessions. def remember self.remember_token = User.new_token update_attribute(:remember_digest, User.digest(remember_token)) end # Returns true if the given token matches the digest. def authenticated?(remember_token) return false if remember_digest.nil? BCrypt::Password.new(remember_digest).is_password?(remember_token) end # Forgets a user. def forget update_attribute(:remember_digest, nil) end end
看来你正在使用Rails 5教程，但是使用Rails 4.在Rails 5中，所有模型都inheritance自ApplicationRecord ，而来自ActiveRecord::Base Rails 4
立即修复：
class User < ActiveRecord::Base ... end
长期修复，切换到Rails 5并学习Rails 5
参考https://stackoverflow.com/a/41388844/5598043的注入答案
使用以下内容创建名为app/models/application_record.rb的新文件：
class ApplicationRecord < ActiveRecord::Base self.abstract_class = true end