Rails无法为nil：NilClass呈现JSON未定义方法“ new”

Question

背景

我正在制作一个具有两个名称空间的Rails应用程序，这两个名称空间分别是admin （用于管理员目的）和api用于移动和网络客户端）。

昨天发生了一件奇怪的事。 我在PostgreSQL数据库中建立了一个新的表facilities ，其中包括id ， name ， created_at ， updated_at 。

问题

我尝试使用admin名称空间http：// localhost：3000 / admin / facilities获取所有功能，并且效果很好（返回HTML和功能列表）。

Started GET "/admin/facilities" for ::1 at 2015-05-10 16:12:47 +0800
Processing by Admin::FacilitiesController#index as HTML
  Facility Load (0.4ms)  SELECT "facilities".* FROM "facilities"
  Rendered admin/facilities/index.html.erb within layouts/application (2.5ms)
Completed 200 OK in 91ms (Views: 90.4ms | ActiveRecord: 0.4ms)

但是，当我从浏览器调用http：// localhost：3000 / api / v1 / facilities时，该浏览器应该返回JSON。 我有一个错误

Api :: V1 :: FacilitiesController＃index中的NoMethodError为nil：NilClass未定义的方法'new'

Extracted source (around line #8):
6  def index
7    @facilities = Facility.all
8    render json: @facilities
9  end
10
11

控制台错误

Started GET "/api/v1/facilities" for ::1 at 2015-05-10 16:38:26 +0800
Processing by Api::V1::FacilitiesController#index as HTML
  User Load (0.6ms)  SELECT  "users".* FROM "users" WHERE "users"."id" IS NULL  ORDER BY "users"."id" ASC LIMIT 1
  Facility Load (0.5ms)  SELECT "facilities".* FROM "facilities"
Completed 500 Internal Server Error in 6ms (ActiveRecord: 1.1ms)

NoMethodError (undefined method `new' for nil:NilClass):
  app/controllers/api/v1/facilities_controller.rb:8:in `index'


  Rendered /Users/abrahamks/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.1/lib/action_dispatch/middleware/templates/rescues/_source.erb (7.1ms)
  Rendered /Users/abrahamks/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.1/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (2.7ms)
. . . .
. . . .
and so on

我从rails c检查并调用Facility.all ，看起来像命令行返回正确的值，但是我不明白为什么它不能呈现/返回json。

Loading development environment (Rails 4.2.1)
2.2.1 :001 > Facility.all
  Facility Load (0.5ms)  SELECT "facilities".* FROM "facilities"
 => #<ActiveRecord::Relation [#<Facility id: 1, name: "Kitchen", created_at: "2015-05-09 10:54:00", updated_at: "2015-05-09 16:08:48">, #<Facility id: 2, name: "Washer", created_at: "2015-05-09 11:20:40", updated_at: "2015-05-09 16:09:32">, #<Facility id: 3, name: "Swimming Pool", created_at: "2015-05-09 11:22:19", updated_at: "2015-05-09 16:09:41">, #<Facility id: 4, name: "Internet", created_at: "2015-05-09 11:24:02", updated_at: "2015-05-09 16:12:31">, #<Facility id: 5, name: "Dryer", created_at: "2015-05-09 15:55:36", updated_at: "2015-05-09 16:12:54">]> 

我的代码有什么问题？ 有没有我错过的配置？ 谢谢。

如果需要更多详细信息

＃GET / facilities / 1 facilities与properties具有多对多关系，我生成一个联接表

class CreateJoinTablePropertiesFacilities < ActiveRecord::Migration
  def change
    create_join_table :properties, :facilities do |t|
      t.index [:property_id, :facility_id]
      t.index [:facility_id, :property_id]
    end
  end
end

这是我的facility.rb

class Facility < ActiveRecord::Base
    has_and_belongs_to_many :property, join_table: :facilites_properties
end

这是我的routes.rb

Rails.application.routes.draw do
  namespace :admin do
    resources :facilities
  end

  namespace :api do
    namespace :v1 do
      resources :properties
      resources :facilities, only: [:index, :show]
      resources :users do
        member do
        post 'list', :to => "users#list_property"
    end
  end

这是我的app/controllers/api/v1/facilities_controller

class Api::V1::FacilitiesController < ApplicationController
  before_action :set_facility, only: [:show, :edit, :update, :destroy]
  # before_action :authenticate
  # GET /facilities
  # GET /facilities.json
  def index
    @facilities = Facility.all
    render json: @facilities
  end

  # GET /facilities/1
  # GET /facilities/1.json
  def show
    render json: @facility
  end

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

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

这是app/controllers/admin/facilities_controller

class Admin::FacilitiesController < ApplicationController
  before_action :set_facility, only: [:show, :edit, :update, :destroy]
  # before_action :authenticate
  # GET /facilities
  # GET /facilities.json
  def index
    @facilities = Facility.all
  end

  # GET /facilities/1
  # GET /facilities/1.json
  def show
  end

  # GET /facilities/new
  def new
    @facility = Facility.new
  end

  # GET /facilities/1/edit
  def edit
  end

  # POST /facilities
  # POST /facilities.json
  def create
    @facility = Facility.new(facility_params)

    respond_to do |format|
      if @facility.save
        format.html { redirect_to admin_facilities_path, notice: 'Facility was successfully created.' }
        format.json { render :show, status: :created, location: @facility }
      else
        format.html { render :new }
        format.json { render json: @facility.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /facilities/1
  # PATCH/PUT /facilities/1.json
  def update
    respond_to do |format|
      if @facility.update(facility_params)
        format.html { redirect_to admin_facilities_path, notice: 'Facility was successfully updated.' }
        format.json { render :show, status: :ok, location: @facility }
      else
        format.html { render :edit }
        format.json { render json: @facility.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /facilities/1
  # DELETE /facilities/1.json
  def destroy
    @facility.destroy
    respond_to do |format|
      format.html { redirect_to facilities_url, notice: 'Facility was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

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

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

Answer 1

堆栈跟踪显示请求已作为HTML处理。

Processing by Admin::FacilitiesController#index as HTML

在尝试呈现JSON时，您可以指定控制器以响应JSON

module Api
  module V1
    class FacilitiesController < ApplicationController
      respond_to :json
    end
  end
end

或者，您可以在route.rb文件中将json指定为默认响应

namespace :api, defaults: { format: 'json' }  do
  # your api json routes...
end

希望这些帮助之一。

Answer 2

我只是意识到我忘记了生成序列化器。 由于我使用gem Active Model序列化程序，因此这就是生成序列化程序的工作。

rails g serializer facility