nil 的未定义方法“downcase”：NilClass railstutorial答案

【问题标题】：undefined method `downcase' for nil:NilClass railstutorialnil 的未定义方法“downcase”：NilClass railstutorial
【发布时间】：2013-12-14 15:03:35
【问题描述】：

我试试 railstutorial rails4.0

现在 9.2.0 并且没有 Rspec 错误。

但是rails s 在打开 /users 时在 Users#index 中有 NoMethodError

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/controllers/users_controller.rb

class UsersController < ApplicationController
  before_action :signed_in_user, only: [:index, :edit, :update]
  before_action :correct_user, only: [:edit, :update]

  def index
    @users = User.all
  end

  def show
    @user = User.find(params[:id])
  end

  def new
    @user = User.new
  end

  def create
    @user = User.new(user_params)
    if @user.save
      sign_in @user
      flash[:success] = "Welcome to the Sample App!"
      redirect_to @user
    else
      render 'new'
    end
  end

  def edit
  end

  def update
    if @user.update_attributes(user_params)
      flash[:success] = "Profile updated"
      redirect_to @user
    else
      render 'edit'
    end
  end

  private

    def user_params
      params.require(:user).permit(:name, :email, :password, :password_confirmation)
    end

    #Before actions

    def signed_in_user
      unless signed_in?
        store_location
        redirect_to signin_url, notice: "Please sign in."
      end
    end

    def correct_user
      @user = User.find(params[:id])
      redirect_to(root_path) unless current_user?(@user)
    end
end

app/views/users/index.html.slim

- provide(:title, 'All users')
h1 All users
ul.users
  - @users.each do |user|
    li
      = gravatar_for user, size: 52
      = link_to user.name, user

app/helpers/users_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

【问题讨论】：

规范答案是def nil.downcase; '' end，错误消失了。
可能有些用户没有电子邮件。尝试打印所有用户记录以检查。

标签： ruby-on-rails railstutorial.org

【解决方案1】：

我没试过。但它可以是这样的。

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

【讨论】：

【解决方案2】：

您的错误似乎来自gravatar_for 方法的第一行，该方法调用user.email.downcase，这表明您在数据库中至少有一个用户的电子邮件地址为nil。

【讨论】：