用于nil的未定义方法`email':NilClass link.user.email

Question

在我的index.html.erb文件中,我收到了一个未定义的电子邮件方法.我进入rails控制台并尝试运行User.first.email,它运行良好.我尝试取出电子邮件并运行link.user,这也很有用.当用户绑定到链接并且用户有电子邮件时,我不确定为什么电子邮件是未定义的.我正在寻找一些可能出错的建议.

Index.html.erb

<%= link.user.email %>

迁移的架构已经运行

create_table "users", force: :cascade do |t|
    t.string   "email",                  default: "", null: false

楷模:

class Link < ActiveRecord::Base
    belongs_to :user
    validates :user, presence: true
    acts_as_votable
    attr_accessor :avatar
    mount_uploader :avatar, AvatarUploader
end

class User < ActiveRecord::Base
    has_many :links
    acts_as_voter
    devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable
end

链接控制器:

class LinksController < ApplicationController
  before_filter :authenticate_user!, except: [:index, :show]

  def index
    @links = Link.all
  end

  def show
    @link = Link.find(params[:id])
  end

  def new
    @link = Link.new
  end

  def edit
  end

  def create
    @link = Link.new(link_params)

    if @link.save
      redirect_to root_path
    else
      render 'new'
    end
  end

    private
    def link_params
      params.require(:link).permit(:title, :url, :avatar, :user_id)
    end
end

错误信息:

User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ?  ORDER BY "users"."id" ASC LIMIT 1  [["id", 1]]
   (0.1ms)  begin transaction
   (0.1ms)  rollback transaction
  Rendered links/_form.html.erb (2.7ms)
  Rendered links/new.html.erb within layouts/application (3.8ms)
Completed 200 OK in 505ms (Views: 143.6ms | ActiveRecord: 0.4ms)

Answer 1

undefined method `email' for nil:NilClass link.user.email

您收到此错误link.user是nil因为某些链接,因此它调用nil.email并失败并显示上述错误消息.

您可以使用try来摆脱这个问题,如下所示:

<%= link.user.try(:email) %>

这样,你的程序将无法即使崩溃link.user是nil对一些案件.