似乎无法为此找到合适的答案。我正在使用Rails教程的第10章第10.1.2节，似乎无法使邮件预览工作。我发现处理错误的所有答案都与本教程的不同部分有关，我假设我正在制作的错误正在盯着我。我已经完成了将教程中的代码复制/粘贴到相关文件中，到目前为止还没有看到我输入的内容和教程中的内容之间的区别。到目前为止，建议是从函数定义中添加或删除参数user，但这还没有解决问题。触发错误的网址为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也没有问题（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
摘录来源：
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
development.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
并且为了完整性，以下是视图和我的用户模型：
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＆lt;％= @ user.name％＆gt;，
Welcome to the Sample App. Click on the link below to activate your account:
<%= edit_account_activation_url(@user.activation_token, email: @user.email) %>
user.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
答案 0 :(得分：5)
哇，很多调试和混乱发现一个非常简单的问题：我没有登录，并且没有为那些试图访问该页面的人定义任何类型的错误消息他们没有登录（因此user.activation_token方法触发Nil:NilClass错误）。这似乎是为什么TDD可以提供帮助的一个很好的例子。
答案 1 :(得分：3)
不确定您的登录是否是问题，而是没有用户。
您是否运行bundle exec rake db:seed来填充？同样在您的控制台中，检查您的数据库是否按预期填充...如果它还没有检查您的＆＃34; seed.rb＆＃34;文件和创建用户的部分确保activated: true存在，如下所示：
User.create!(name: "Example User",
email: "testing@akqa.com",
password: "foobar",
password_confirmation: "foobar",
admin: true,
** activated: true,
activated_at: Time.zone.now)
上面提到的错误'activation_token=' for nil:NilClass实际上似乎是因为没有用户。
当你提到你＆＃34;登录＆＃34;您可能实际上只是重新注册，从而创建了使此功能工作所需的用户。希望这有帮助！
答案 2 :(得分：0)
如果它和我一样的错误，你的数据库没有数据和user.first检索NIL而不是下一行不工作。 检查您的种子文件和db。