Rails 4：模型：类的未定义方法“relation_delegate_class”

Question

我正在尝试关注这个关于 Creating a Scoped Invitation System for Rails 的 coderwall 教程。

在我的 Rails 4 应用程序中，我有以下模型：

class User < ActiveRecord::Base
  has_many :administrations
  has_many :calendars, through: :administrations
  has_many :invitations, :class_name => "Invite", :foreign_key => 'recipient_id'
  has_many :sent_invites, :class_name => "Invite", :foreign_key => 'sender_id'
end

class Calendar < ActiveRecord::Base
  has_many :administrations
  has_many :users, through: :administrations
  has_many :invites
end

class Administration < ActiveRecord::Base
  belongs_to :user
  belongs_to :calendar
end

class Invite < ActiveRecord::Base
  belongs_to :calendar
  belongs_to :sender, :class_name => 'User'
  belongs_to :recipient, :class_name => 'User'
end

这是我的模型和教程中的模型之间的对应关系：

• User User
• Calendar UserGroup
• Administration Membership
• Invite Invite

我现在在发出新邀请部分：

• Invite 模型已更新为 before_create 过滤器和 generate_token 方法。
• Invites 控制器已更新为 create 操作。

但是，当我访问日历编辑视图以填写邀请表单时，我收到以下错误：

NoMethodError in CalendarsController#edit
undefined method `relation_delegate_class' for Invite:Class
def edit
  @user = current_user
  @invite = @calendar.invites.build
  authorize @calendar
end

问题似乎来自@invite = @calendar.invites.build 行。

————

更新：这是我的邀请模型的内容：

class Invite < ActiveRecord::Base
  belongs_to :calendar
  belongs_to :sender, :class_name => 'User'
  belongs_to :recipient, :class_name => 'User'

  before_create :generate_token

  def generate_token
   self.token = Digest::SHA1.hexdigest([self.calendar_id, self.recipient_role, Time.now, rand].join)
  end

end

————

UPDATE 2：在this question，作者解释问题可能来自CanCanCan & Rolify。我不使用这些宝石，但我使用 Pundit。认为这对我的问题很有用。

————

更新 3：这也是我用于 Invite 模型的迁移：

class CreateInvites < ActiveRecord::Migration
  def change
    create_table :invites do |t|
      t.string :email 
      t.integer :calendar_id
      t.integer :sender_id
      t.integer :recipient_id
      t.string :recipient_role
      t.string :token
      t.timestamps null: false
    end
  end
end

我想知道问题是否可能是由t.string :recipient_role 引起的，因为给定user 的role 仅存在于administration 表中，对于给定的calendar：如果:recipient_role 是Rails 自动将其解释为recipient.role，那么这可能是导致错误的原因吗？

————

更新 4：这是 CalendarsController 的内容：

class CalendarsController < ApplicationController
  before_action :set_calendar, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!

  # GET /calendars
  # GET /calendars.json
  def index
    @user = current_user
    @calendars = @user.calendars.all
  end

  # GET /calendars/1
  # GET /calendars/1.json
  def show
    @user = current_user
    @calendar = @user.calendars.find(params[:id])
    authorize @calendar
  end

  # GET /calendars/new
  def new
    @user = current_user
    @calendar = @user.calendars.new
    authorize @calendar
  end

  # GET /calendars/1/edit
  def edit
    @user = current_user
    @invite = @calendar.invites.build
    authorize @calendar
  end

  # POST /calendars
  # POST /calendars.json
def create
  @user = current_user
  @calendar = @user.calendars.create(calendar_params)
  authorize @calendar
  respond_to do |format|
    if @calendar.save
      current_user.set_default_role(@calendar.id, 'Owner')
      format.html { redirect_to calendar_path(@calendar), notice: 'Calendar was successfully created.' }
      format.json { render :show, status: :created, location: @calendar }
    else
      format.html { render :new }
      format.json { render json: @calendar.errors, status: :unprocessable_entity }
    end
  end
end

  # PATCH/PUT /calendars/1
  # PATCH/PUT /calendars/1.json
  def update
    @user = current_user
    @calendar = Calendar.find(params[:id])
    authorize @calendar
    respond_to do |format|
      if @calendar.update(calendar_params)
        format.html { redirect_to calendar_path(@calendar), notice: 'Calendar was successfully updated.' }
        format.json { render :show, status: :ok, location: @calendar }
      else
        format.html { render :edit }
        format.json { render json: @calendar.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /calendars/1
  # DELETE /calendars/1.json
  def destroy
    @user = current_user
    @calendar.destroy
    authorize @calendar
    respond_to do |format|
      format.html { redirect_to calendars_url, notice: 'Calendar was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_calendar
      @calendar = Calendar.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def calendar_params
      params.require(:calendar).permit(:name)
    end
end

————

UPDATE 5：这里是服务器日志：

Started GET "/calendars/2/edit" for ::1 at 2015-09-14 11:44:13 -0700
Processing by CalendarsController#edit as HTML
  Parameters: {"id"=>"2"}
  Calendar Load (0.1ms)  SELECT  "calendars".* FROM "calendars" WHERE "calendars"."id" = ? LIMIT 1  [["id", 2]]
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ?  ORDER BY "users"."id" ASC LIMIT 1  [["id", 1]]
Completed 500 Internal Server Error in 3ms (ActiveRecord: 0.3ms)

NoMethodError (undefined method `relation_delegate_class' for Invite:Class):
  app/controllers/calendars_controller.rb:30:in `edit'


  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/_source.erb (6.0ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (2.8ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (1.7ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout (68.9ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_markup.html.erb (0.5ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_inner_console_markup.html.erb within layouts/inlined_string (0.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_prompt_box_markup.html.erb within layouts/inlined_string (0.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/style.css.erb within layouts/inlined_string (0.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/console.js.erb within layouts/javascript (39.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/main.js.erb within layouts/javascript (0.4ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/error_page.js.erb within layouts/javascript (0.4ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/index.html.erb (94.2ms)

————

更新 6：我才意识到我没有

def invite_params
  params.require(:invite)
end

在Invites 控制器中：这可能是问题的根源吗？

————

您知道此错误消息的含义以及如何解决此问题吗？

Answer 1

这个问题很难识别，尤其是从问题的内容来看。

问题

我收到 undefined method 'relation_delegate_class' for Invite:Class 错误的原因是 Invite 不再被 Rails 视为模型。

问题的根本原因

当我创建Invite 邮件程序时，我运行的是rails g mailer Invite 而不是rails g mailer InviteMailer。

因此，Invite 作为邮件程序会覆盖 Invite 作为模型，因此一旦将方法应用于 Invite 模型的实例就会产生错误。

我们是怎么想出来的

我的一个朋友在编程方面比我更有经验，他通过调整导致错误的 @invite = @calendar.invites.build 行发现了问题。

这导致我们最终在 Rails 控制台中运行 Invite.first：虽然我们应该得到 Invite 类的实例或 nil，但我们实际上得到了一个错误。

由于.first 应该是任何 ActiveRecord 模型上的有效方法，我们意识到 Invite 不被 Rails 视为模型。

我们是如何解决的

一旦我们确定了问题，修复它就非常简单：

• 我们将 Invite 邮件程序的名称从 invite.rb 更改为 invite_mailer.rb
• 在新重命名的invite_mailer.rb 文件中，我们将class Invite < ApplicationMailer 替换为class InviteMailer < ApplicationMailer

我希望这对可能遇到类似relation_delegate_class 错误的其他 Stack Overflow 用户有用。

Answer 2

如果您忘记从 ActiveRecord 继承模型，也会发生这种情况。 因此它变成了一个简单的 ruby​​ 类。

class MyPlainModel
end

Answer 3

另一个原因是您的 sti 列指向无效的列类。我以某种方式结束了：

=> #<Mailerlite::Subscriber:0x00005559d469bd00
...
 user_id: 2777,
 user_type: "NilClass",
...
>

在尝试加载user 关系时导致NoMethodError: undefined method 'relation_delegate_class' for NilClass:Class。

只需将user_type 列更改为nil 或正确的类名即可轻松解决。