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

型号：

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

错误讯息：

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

class Foo
  constructor: ->
    @list = []

您收到此错误是因为某些链接undefined method `email' for nil:NilClass link.user.email为link.user，因此会调用nil并因上述错误消息而失败。

您可以使用try来解决此问题：

nil.email

这样，即使某些情况下<%= link.user.try(:email) %>为link.user，您的程序也不会崩溃。

Answer 2

此错误的原因是link.user是nil。您必须检查它是否为nil：

<% if !link.user.nil? %>
  <%= link.user.email %>
<% end %>

Answer 3

特定nil可能会有email nil user您可以使用try逃离undefined method for NilClass

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

如果user的{{1}}为零，则会保存您

或

link

Answer 4

我知道你接受了另一个答案，但我认为这是不正确的。

错误表示您没有user的关联link对象。

如果您希望每个link拥有关联的user，那么您最好使用validation确保＆create ＃39;出现在update或#app/models/link.rb class Link < ActiveRecord::Base belongs_to :user validates :user, presence: true end：

link

这意味着每次创建User时，都有拥有.nil?个对象;首先防止错误。

-

如果您需要运行应用程序的方式（IE只有用户可以发布链接或其他内容），那么您将不再需要.try()或public class TestActivity extends AppCompatActivity { private Handler mHandler = new Handler(); //private long mStartRX = 0; //private long mStartTX = 0; private long mLastRX = 0;//Store Last RX data private long mLastTX = 0;//Store Last TX data @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_tv_remote); mLastRX = TrafficStats.getTotalRxBytes(); //Set initial RX data mLastTX = TrafficStats.getTotalTxBytes(); //Set initial TX data if (mStartRX == TrafficStats.UNSUPPORTED || mStartTX == TrafficStats.UNSUPPORTED) { AlertDialog.Builder alert = new AlertDialog.Builder(this); alert.setTitle("Uh Oh!"); alert.setMessage("Your device does not support traffic stat monitoring."); alert.show(); } else { mHandler.postDelayed(mRunnable, 1000); } // } private void calculate() { long rxBytes = TrafficStats.getTotalRxBytes(); // Latest RX data long rxSpeed = rxBytes - mLastRX; // Diff = Latest RX data - Last RX Data Log.i("TAG", "Speed RX:"+rxSpeed); mLastRX = rxBytes; //Set last RX data as Current RX data RX.setText(Long.toString(rxSpeed) + " bytes"); if (rxSpeed >= 1024) { // KB or more long rxKb = rxSpeed / 1024; RX.setText(Long.toString(rxKb) + " KBs"); if (rxKb >= 1024) { // MB or more long rxMB = rxKb / 1024; RX.setText(Long.toString(rxMB) + " MBs"); if (rxMB >= 1024) { // GB or more long rxGB = rxMB / 1024; RX.setText(Long.toString(rxGB)); }// rxMB>1024 }// rxKb > 1024 }// rxSpeed>=1024 long txBytes = TrafficStats.getTotalTxBytes(); // Latest TX data long txSpeed = txBytes - mLastTX; // Diff = Latest TX data - Last TX Data mLastTX = txBytes; //Set last TX data as Current TX data Log.i("TAG", "Speed TX:"+txSpeed); TX.setText(Long.toString(txSpeed) + " bytes"); if (txSpeed >= 1024) { // KB or more long txKb = txSpeed / 1024; TX.setText(Long.toString(txKb) + " KBs"); if (txKb >= 1024) { // MB or more long txMB = txKb / 1024; TX.setText(Long.toString(txMB) + " MBs"); if (txMB >= 1024) { // GB or more long txGB = txMB / 1024; TX.setText(Long.toString(txGB)); }// rxMB>1024 }// rxKb > 1024 }// rxSpeed>=1024 } }条件语句图。

简而言之，我认为接受的答案就像画画一样生锈（没有冒犯等）。

Answer 5

我认为您需要检查链接迁移文件

onChildUpdated

在此文件中，您需要class CreateLinks < ActiveRecord::Migration

未定义的方法`email＆＃39; for nil：NilClass link.user.email

5 个答案: