似乎无法为此找到有效的答案。我正在阅读 Rails 教程的第 10 章第 10.1.2 节，但似乎无法使邮件程序预览正常工作。我发现处理错误的所有答案都与教程的不同部分相关，我假设我犯的错误正盯着我的脸。我已经完成并将教程中的代码复制/粘贴到相关文件中，但到目前为止，我还看不出我输入的内容与教程中的内容有什么区别。到目前为止，建议是在函数定义中添加或删除参数 user，但这并没有解决问题。触发错误的 url 是 http://localhost:3000/rails/mailers/user_mailer/account_activation . http://localhost:3000/rails/mailers/user_mailer/没有问题，http://localhost:3000/rails/mailers/user_mailer/password_reset 也没有(我还没有做任何定制)。我错过了什么？

这是错误:

    NoMethodError in Rails::MailersController#preview
    undefined method `activation_token=' for nil:NilClass

提取源:

def account_activation
  user = User.first
  user.activation_token = User.new_token # highlighted line
  UserMailer.account_activation(user)
end

据我所知，这里涉及的文件是:

user_mailer.rb:

     class UserMailer < ApplicationMailer

       # Subject can be set in your I18n file at config/locales/en.yml
       # with the following lookup:
       #
       #   en.user_mailer.account_activation.subject
       #
       def account_activation(user)
         @user = user
         mail to: user.email, subject: "Account activation"
       end

       def password_reset
         @greeting = "Hi"

         mail to: "to@example.org"
       end
     end

user_mailer_preview.rb:

     # Preview all emails at http://localhost:3000/rails/mailers/user_mailer
     class UserMailerPreview < ActionMailer::Preview

       # Preview this email at http://localhost:3000/rails/mailers/user_mailer/account_activation
       def account_activation
         user = User.first
         user.activation_token = User.new_token
         UserMailer.account_activation(user)
       end

       # Preview this email at http://localhost:3000/rails/mailers/user_mailer/password_reset
       def password_reset
         UserMailer.password_reset
       end

     end

开发.rb:

    Rails.application.configure do

      config.cache_classes = false

      # Do not eager load code on boot.
      config.eager_load = false

      # Show full error reports and disable caching.
      config.consider_all_requests_local       = true
      config.action_controller.perform_caching = false

      # Don't care if the mailer can't send.
      config.action_mailer.raise_delivery_errors = true
      config.action_mailer.delivery_method = :test
      host = 'localhost:3000'
      config.action_mailer.default_url_options = { host: host }

      # Print deprecation notices to the Rails logger.
      config.active_support.deprecation = :log

      # Raise an error on page load if there are pending migrations.
      config.active_record.migration_error = :page_load

      # Debug mode disables concatenation and preprocessing of assets.
      # This option may cause significant delays in view rendering with a large
      # number of complex assets.
      config.assets.debug = true

      # Asset digests allow you to set far-future HTTP expiration dates on all assets,
      # yet still be able to expire them through the digest params.
      config.assets.digest = true

      # Adds additional error checking when serving assets at runtime.
      # Checks for improperly declared sprockets dependencies.
      # Raises helpful error messages.
      config.assets.raise_runtime_errors = true

      # Raises error for missing translations
      # config.action_view.raise_on_missing_translations = true
    end

为了完整起见，这里是 View 和我的用户模型:

account_activation.html.erb:

    <h1>Sample App</h1>

    <p>Hi <%= @user.name %>,</p>

    <p>
    Welcome to the Sample App! Click on the link below to activate your account:
    </p>

    <%= link_to "Activate", edit_account_activation_url(@user.activation_token,
                                                        email: @user.email) %>

account_activation.text.erb: 嗨 <%= @user.name %>,

    Welcome to the Sample App. Click on the link below to activate your account:

    <%= edit_account_activation_url(@user.activation_token, email: @user.email) %>

用户.rb:

    class User < ActiveRecord::Base
      attr_accessor :remember_token, :activation_token
      before_save   :downcase_email
      before_create :create_activation_digest
      validates :name,  presence: true, length: { maximum: 50 }
      VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-]+(\.[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, length: { minimum: 6 }, allow_blank: true

      # 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

      private

        # Converts email to all lower-case.
        def downcase_email
          self.email = email.downcase
        end

        # Creates and assigns the activation token and digest.
        def create_activation_digest
          self.activation_token  = User.new_token
          self.activation_digest = User.digest(activation_token)
        end
    end

最佳答案

哇，为了发现一个真正简单的问题进行了大量的调试和混淆:我没有登录，并且没有为那些试图在没有登录的情况下访问该页面的人定义任何类型的错误消息(因此user.activation_token 方法触发了 Nil:NilClass 错误)。这似乎是为什么 TDD 可以提供大量帮助的一个很好的例子。

关于ruby-on-rails - Rails 中的 NoMethodError::MailersController#preview undefined method `activation_token=' for nil:NilClass，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28906641/