ruby-on-rails - 未定义的方法 `admin?' 为 nil :NilClass

Question

我关注了 railscast #250 Authentication from Scratch 并且一切正常。现在我试图只在我的索引页面上显示编辑和销毁链接到管理员用户的。

我已经使用管理员 bool 字段设置了 mu 用户数据库，并尝试在另一个模型(远足径)的 View 中放置一个简单的 if 语句，以仅显示指向管理员用户的某些链接，但是在我尝试时出现此错误，undefined method 'admin?' for nil:NilClass
数据库架构

  create_table "users", :force => true do |t|
    t.string   "email"
    t.string   "password_digest"
    t.boolean  "admin"
    t.datetime "created_at",      :null => false
    t.datetime "updated_at",      :null => false
  end

用户模型

class User < ActiveRecord::Base
  attr_accessible :email, :password, :password_confirmation#, :admin

  validates :email, :uniqueness => true

  has_secure_password
end

应用 Controller

class ApplicationController < ActionController::Base
  protect_from_forgery

  # fetch the currently logged-in user record to see if the user is currently logged in
  # putting this method in ApplicationController so that it’s available in all controllers
  private
  def current_user
    # checks for a User based on the session’s user id that was stored when they logged in, and stores result in an instance variable
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end
  # to give access to this method from all the views, the helper_method makes it a helper method
  helper_method :current_user

  # basic authorization, user must be logged in!
  def authorize
    redirect_to login_url, alert: "You must be logged in to perform this action" if current_user.nil?
  end
end

意见/远足径/index.html.erb

  <% if current_user.admin? %>
    <%= link_to t('.edit', :default => t("helpers.links.edit")),
              edit_hikingtrail_path(hikingtrail), :class => 'btn btn-mini' %>
    <%= link_to t('.destroy', :default => t("helpers.links.destroy")),
              hikingtrail_path(hikingtrail),
              :method => :delete,
              :data => { :confirm => t('.confirm', :default => t("helpers.links.confirm", :default => 'Are you sure?')) },
              :class => 'btn btn-mini btn-danger' %>
  <% end %>

Answer 1

current_user如果用户未根据您的代码登录，则为零。所以你需要这样做:

<% if current_user && current_user.admin? %>

或使用 try Rails 添加到所有对象的方法。

<% if current_user.try(:admin?) %>