Rails为nil：NilClass使用的未定义方法`user'

Question

Hello everyone I am new to rails and for some reason I keep getting an error

undefined method 'user' for nil:NilClass .

I have pasted an image of the error on the bottom and I posted the code below.

Image Error

# registeredapps_controller.rb

class RegisteredappsController < ApplicationController

 def create
   @registeredapp = Registeredapp.new(registeredapp_params)
   @registeredapp.user = current_user

  unless RegisteredappPolicy.new(current_user, @registeredapp).create?
    flash[:alert] = "not authorized" 
    redirect_to user_registeredapps_path(current_user.id)
  end

  if @registeredapp.save
    flash[:notice] = "You successfully registered your app."
    redirect_to user_registeredapp_path(current_user.id, @registeredapp.id)
  else
    flash.now[:alert] = "There was an error registering your app. Please try again."
    render :new
  end
end

Policies (using Pundit Gem)
# registeredapp_policy.rb

class RegisteredappPolicy 

  def initialize(user, registeredapp)
    @registeredapp = registeredapp
    @user = user
  end

  def create?
    if @user.present?
     @user = @registerdapp.user
    else
     false
  end
end

Here are my models

# models/user.rb

class User < ApplicationRecord

  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
     :recoverable, :rememberable, :trackable, :validatable, :confirmable

  def avatar_url(size)
    gravatar_id = Digest::MD5::hexdigest(self.email).downcase
    "http://gravatar.com/avatar/#{gravatar_id}.png?s=#{size}"
  end

  has_many :registeredapps
end

# models/registeredapp.rb

class Registeredapp < ApplicationRecord
  belongs_to :user
  has_many :events
end

Answer 1

Your issue is that the instance variable @registeredapp is mispelled in the RegisteredappPolicy class under the create? method.

It currently is

def create?
  if @user.present?
    @user = @registerdapp.user
  else
    false
  end
end

whereas the variable defined in the initialize is @registeredapp you're missing an e

Answer 2

@registerdapp is nil

@user = @registerdapp.user

use try

@user = @registerdapp.try(:user)

or

def create?
  if @user.present? && @registerdapp.present?
    @user = @registerdapp.user
  else
    false
  end
end

NOTE: Also you are missing one end for if else in create? method

Answer 3

Rails convention usually is to have the model name like:

User

And its corresponding table name like:

users

In your ActiveRecord::Registeredapp you have :user , check if you shouldn't have :users .