未初始化的常量 ApplicationRecord

Question

我正在在线编写 rails 教程书，当我转到 http://localhost:3000/

时收到以下错误消息

"uninitialized constant ApplicationRecord"

它给了我以下突出显示第一行的代码。

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+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  validates :email, presence: true, length: { maximum: 255 },

这是我的 application.html.erb 文件：

<!DOCTYPE html>
<html>
  <head>
    <title><%= full_title(yield(:title)) %></title>
    <%= stylesheet_link_tag "application", media: "all",
                                           "data-turbolinks-track" => true %>
    <%= javascript_include_tag "application", "data-turbolinks-track" => true %>
    <%= csrf_meta_tags %>
    <%= render 'layouts/shim' %>
  </head>
  <body>
    <%= render 'layouts/header' %>
    <div class="container">
      <% flash.each do |message_type, message| %>
        <div class="alert alert-<%= message_type %>"><%= message %></div>
      <% end %>
      <%= yield %>
      <%= render 'layouts/footer' %>
      <%= debug(params) if Rails.env.development? %>
    </div>
  </body>
</html>

还有我的 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+\-.]+@[a-z\d\-.]+\.[a-z]+\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

Answer 1

看来您使用的是 Rails 5 教程，但使用的是 Rails 4。在 Rails 5 中，所有模型都继承自 ApplicationRecord，而 Rails 4 来自 ActiveRecord::Base

立即修复：

class User < ActiveRecord::Base
...
end

长期修复，切换到 Rails 5 并学习 Rails 5

Answer 2

参考

中 infused 的回答

创建一个名为 app/models/application_record.rb 的新文件，内容如下：

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
end

Answer 3

如果您在从 Rails 5 移动到 Rails 6 后遇到此问题，请确保更改

config.load_defaults 5.2

为了

config.load_defaults 6.0

在您的 config/application.rb 文件中。

未初始化的常量 ApplicationRecord

uninitialized constant ApplicationRecord

ruby-on-rails

ruby

ruby-on-rails-4

localhost

railstutorial.org