NoMethodError at / undefined method `name' for nil:NilClass

问题

I have tried many solution and came up with good one but still getting error. I am editing my whole question.

I am trying to create Friendly URL with friendly_id gem. In my project First user need to signup with devise. Devise will pass some information to profile model with

model/user.rb

delegate :age, :city, :region, :country, to: :profile

I want to make user.name to be Friendly_id candidate. I have tried following code in my Profile model:-

 class Profile < ActiveRecord::Base

       extend FriendlyId
      friendly_id :user_name , use: :slugged 

       def user_name
       user.name
       end

But it is giving error

NoMethodError at / undefined method `name' for nil:NilClass

now After submitting user form.

Please suggest possible solution with explanation.

My User.rb looks like

require 'open-uri'

class User < ActiveRecord::Base
  paginates_per 10

  validates :name , presence: true, length: { maximum: 200 }

  scope :by_name, ->(name) do
    joins(:profile).where('lower(name) LIKE ?', "%#{name.downcase}%")
  end  

  delegate :age, :city, :region, :country, to: :profile

  has_one :profile, dependent: :destroy
  accepts_nested_attributes_for :profile


      def self.new_with_session(params, session)
        session_params = { 'profile_attributes' => {} }

        provider = session['devise.provider']
        if provider && data = session["devise.#{provider}"]
          session_params['name'] = data[:name] if data[:name]
          session_params['email'] = data[:email] if data[:email]
          session_params['profile_attributes'] =
            { avatar: data[:image] } if data[:image]
        end

        params.deep_merge!(session_params)
        super.tap do |user|
          if auth = Authorization.find_from_session(session, provider)
            user.authorizations << auth
          end
        end
      end

      def password_required?
        super && registered_manually?
      end

      def registered_manually?
        encrypted_password.present?
      end

    end

And my profile.rb looks like

class Profile < ActiveRecord::Base

   extend FriendlyId
    friendly_id user.name, use: :slugged 


  belongs_to :user
  accepts_nested_attributes_for :user


  validates :website, allow_blank: true, uri: true

  def website=(url_str)
    if url_str.present?
      url_str = "http://#{url_str}" unless url_str[/^https?/]
      write_attribute :website, url_str
    end
  end    

end

I think Problem is here:

Request parameters  
{"action"=>"new", "controller"=>"users/registrations"}
Please suggest possible solution and explanation. 

And users/registration:

class Users::RegistrationsController < Devise::RegistrationsController
  layout 'land'

  def create
    params[:user][:profile_attributes].delete(:place)

  end  
  protected

    def after_sign_up_path_for(resource)
      welcome_path
    end
end

I am creating user in profile controller

    def load_profile
      @profile = Profile.friendly.find(params[:id])
      if !@profile || @profile.user.blocked_users.include?(current_user)
        redirect_to home_path
      else
        @user = @profile.user
      end
    end

@Rodrigo helped me find out error that error is due to Friendly_id can't create link with user instance.

回答1:

There is an error on this line:

friendly_id user.name, use: :slugged 

The variable user doesn't exists at Profile class scope. You should use something like this:

friendly_id :user_name, use: :slugged 

def user_name
  user.name
end

回答2:

extend FriendlyId
     friendly_id u_name, use: :slugged 
     def u_name
      user.name
     end 
    belongs_to :user

Have you defined user? what is user.name?

来源：https://stackoverflow.com/questions/28051548/nomethoderror-at-undefined-method-name-for-nilnilclass