未定义的方法`gravatar_url”的零：NilClass

Question

我有一个轨道4的应用程序，以崭新的PG数据库中运行，经过20个用户创建我开始收到此错误

ActionView::Template::Error (undefined method `gravatar_url' for nil:NilClass): 

这里是用户。 RB型号：

 def gravatar_url 
     stripped_email = email.strip 
     downcased_email= stripped_email.downcase 
     hash = Digest::MD5.hexdigest(downcased_email) 

     "http://gravatar.com/avatar/#{hash}?r=x" 
     end 

这里是index.html.erb

<% @statuses.each do |status| %> 
<div class="status"> 
    <div class ="row"> 
    <div class="span1"> 
     <%= image_tag status.user.gravatar_url %> 
    </div> 
    <div class="span7"> 
     <strong><%= status.user.full_name %></strong> 
     <p><%= status.content %></p> 
     <div class="meta"> 
     <%= link_to time_ago_in_words(status.created_at) + " ago" , status %> 
     <span class="admin"> 
      | <%= link_to "Edit", edit_status_path(status) %> | 
      <%= link_to "Delete", status, method: :delete, data: { confirm: "Are      you sure you want to delete this status?"} %> 
     </span> 
     </div> 
    </div> 
    </div> 
</div> 

如果我用耙滴数据库，并从头开始DB：迁移它工作得很好，但一旦我打了20个用户，事情开始变坏，应用程序会抛出异常。

这里的状态控制器

class StatusesController < ApplicationController 
    before_action :set_status, only: [:show, :edit, :update, :destroy] 

    before_filter :authenticate_user!, only: [:new, :create, :edit, :update] 


    # GET /statuses 
    # GET /statuses.json 
    def index 
    @statuses = Status.all 
    end 

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

    # GET /statuses/new 
    def new 
    @status = Status.new 
    end 

    # GET /statuses/1/edit 
    def edit 
    end 

    # POST /statuses 
    # POST /statuses.json 
    def create 
    @status = current_user.statuses.new(status_params) 

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

    # PATCH/PUT /statuses/1 
    # PATCH/PUT /statuses/1.json 
    def update 
    @status = current_user.statuses.find(params[:id]) 

    if params[:status] && params[:status].has_key?(:user_id) 
     params[:status].delete(:user_id) 
    end 


    respond_to do |format| 
     if @status.update(status_params) 
     format.html { redirect_to @status, notice: 'Status was successfully updated.' } 
     format.json { head :no_content } 
     else 
     format.html { render action: 'edit' } 
     format.json { render json: @status.errors, status: :unprocessable_entity } 
     end 
    end 
    end 

    # DELETE /statuses/1 
    # DELETE /statuses/1.json 
    def destroy 
    @status.destroy 
    respond_to do |format| 
     format.html { redirect_to statuses_url } 
     format.json { head :no_content } 
    end 
    end 

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

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

下面是状态类：

class Status < ActiveRecord::Base 
    belongs_to :user 

    validates :content, presence: true, 
         length:{ minimum: 2 } 

    validates :user_id, presence: true 

end 

这里是用户等级：

class User < ActiveRecord::Base 
    # Include default devise modules. Others available are: 
    # :token_authenticatable, :confirmable, 
    # :lockable, :timeoutable and :omniauthable 
    devise :database_authenticatable, :registerable, 
     :recoverable, :rememberable, :trackable, :validatable 

    validates :first_name, presence: true 

    validates :last_name, presence: true 

    validates :profile_name, presence: true, 
          uniqueness: true, 
          format: { 
          with: /\A[a-zA-Z0-9_-]+\Z/, 
          message: 'must be formatted correctly.' 
          } 

    has_many :statuses 
end 

和应用程序控制器：

class ApplicationController < ActionController::Base 
    before_filter :configure_permitted_parameters, if: :devise_controller? 

    protect_from_forgery with: :exception 

    protected 

    def configure_permitted_parameters 
    devise_parameter_sanitizer.for(:sign_up) { |u| u.permit(:first_name, :last_name, :profile_name, 
                  :email, :password, :password_confirmation) } 

    devise_parameter_sanitizer.for(:statuses) { |u| u.permit(:user_id)} 
    end 
end 

Answer 1

至少一个不与一个用户相关联。您的观点是抛出一个错误，因为它最终试图访问status.user的gravatarl_url方便的方法，但因为状态没有用户，它抛出一个异常ActionView::Template::Error (undefined method 'gravatar_url' for nil:NilClass):。

试想以下情形：

Status.find(1).user.nil? == false 
Status.find(2).user.nil? == false 
Status.find(3).user.nil? == true # no associated user 
Status.find(4).user.nil? == false 

当您指定Status.all到@statuses实例变量，它会包括所有四种状态 - 包括第三状态，其中有没有相关的用户。当在你看来遍历@statuses，您会收到一个错误，当第三状态循环：

# first pass 
status.user # found 

# second pass 
status.user # found 

# third pass 
status.user # NilClass exception is thrown, causing loop to exit 

要确定哪些状态没有相关的用户，运行以下阿雷尔查询：

Status.joins("left join users on users.status_id = statuses.id").where("users.status_id is null") 
#=> [#<Status id: 3>] 

要解决此错误，只是用户与没有用户的状态相关联：

status = Status.find(3) 
user = User.create 
status.user = user # associates `user` with `status` 

Status.joins("left join users on users.status_id = statuses.id").where("users.status_id is null") 
#=> [] # all statuses are now associated with a user 

UPDATE ：

# app/models/user.rb 
class User < ActiveRecord::Base 
    # ... existing logic 

    before_destroy :find_parent 
    after_destroy :destroy_orphaned_parent 

    def find_parent 
     @parent = self.parent 
    end 

    def destroy_orphaned_parent 
     if @parent.children.length == 0 
      @parent.destroy 
     end 
    end 
end 

Answer 2

问题是status.user返回nil，这意味着没有user_id属性是nil（或NULL，在数据库中）。

另一个选项可为用户不再存在，但我相信，如果你想看看它会抛出一个错误。经由Status.all检索到的状态的