Ruby on rails 未定义的方法'downcase'；对于零：零级铁路结构

我尝试了Railstorial rails4.0

现在是9.2.0，没有Rspec错误

但是

rails s

在用户中有NoMethodError#在打开/Users时索引

为什么?

app/models/user.rb

class User < ActiveRecord::Base
  before_save { self.email = email.downcase }
  before_create :create_remember_token
  validates :name, presence: true, length: { maximum: 50 }
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-]+(\.[a-z]+)*\.[a-z]+\z/i
  validates :email, presence: true, format: { with: VALID_EMAIL_REGEX },
    uniqueness: { case_sensitive: false }
  has_secure_password
  validates :password, length: { minimum: 6 }

  def User.new_remember_token
    SecureRandom.urlsafe_base64
  end

  def User.encrypt(token)
    Digest::SHA1.hexdigest(token.to_s)
  end

  private

    def create_remember_token
      self.remember_token = User.encrypt(User.new_remember_token)
    end
end

app/helpers/users\u helper.rb

module UsersHelper

  # Returns the Gravatar (http://gravatar.com/) for the given user.
  def gravatar_for(user, options = { size: 50 })
    gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
    size = options[:size]
    gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
    image_tag(gravatar_url, alt: user.name, class: "gravatar")
  end
end

---

您的错误似乎来自

gravatar\u for

方法的第一行，该方法调用

user.email.downcase

，表明数据库中至少有一个用户的

nil

电子邮件地址。

我没有尝试过。但也可能是这样

before_save { self.email = email.downcase if email}

---

标准答案是

def nil.downcase；''结束

，错误消失。可能某些用户没有电子邮件。请尝试打印所有用户记录以检查是否存在此问题。

module UsersHelper

  # Returns the Gravatar (http://gravatar.com/) for the given user.
  def gravatar_for(user, options = { size: 50 })
    gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
    size = options[:size]
    gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
    image_tag(gravatar_url, alt: user.name, class: "gravatar")
  end
end

before_save { self.email = email.downcase if email}