在其他控制器和视图中创建用户（Rails 4 with Devise）

我尝试在我的管理控制器中创建用户但不运行它总是会留下一些错误。

我使用 application_helper 登录到我的 root # home with devise 但我不知道这是否是创建用户时导致我更多问题的原因

应用程序/助手/application_helper.rb：

module ApplicationHelper

  def resource_name
   :user
  end
  def resource_name_request
   :request
  end

 def resource
   @resource ||= User.new
 end

 def devise_mapping
   @devise_mapping ||= Devise.mappings[:user]
 end

end

app/controllers/application_controller.rb：应用控制器

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception
  before_action :configure_permitted_parameters, if: :devise_controller?



   def after_sign_in_path_for(resource)
     session[:previous_url] ||
     if current_user.role == "admin"
       admin_index_path
     end

   end

  protected

  def configure_permitted_parameters
    devise_parameter_sanitizer.permit(:sign_up, keys: [:name, :role])
    devise_parameter_sanitizer.permit(:account_update, keys: [:name, :country])
  end   
end

app/models/user.rb: 用户模型

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

  devise :database_authenticatable, :registerable,
  :recoverable, :rememberable, :trackable, :validatable
end

app/controllers/admin_controller.rb: Admin_controller

class AdminController < ApplicationController
      before_action :authenticate_user!


  def index

    @user = User.new
  end


  def create
    request_hash = {
      :name => params[:name],
      :email => params[:email],
      :role => params[:role],
      :password => params[:password],
      :password_confirmation => params[:password_confirmation]
    }
    @user = User.new(request_hash)
    @user.save
  end
end

app/views/admin/index.html.erb ：我现在用来创建的视图（目前是我的问题的根源）

          <%= form_for @user, as: resource_name do |f|  %>
              <%= devise_error_messages! %>
              <div class="field">
                <%= f.label :name %><br />
                <%= f.text_field :name %>
              </div>

              <div class="field">
                <%= f.label :email %><br />
                <%= f.email_field :email, autofocus: true %>
              </div>

              <div class="field">
                <%= f.label :password %>
                <% if @minimum_password_length %>
                <em>(<%= @minimum_password_length %> characters minimum)</em>
                <% end %><br />
                <%= f.password_field :password, autocomplete: "off" %>
              </div>

              <div class="field">
                <%= f.label :password_confirmation %><br />
                <%= f.password_field :password_confirmation, autocomplete: "off" %>
              </div>

                <div class="field">

                  <%= f.select(:role) do %>
                    <% [['Admin', "admin"], ['User', "user"]].each do |c| -%>
                      <%= content_tag(:option, c.first, value: c.last) %>
                    <% end %>
                  <% end %>
                </div>

                <div class="actions">
                    <%= f.submit "Sign up" %>
                </div>
              <% end %>

config/routes.rb: 路由

Rails.application.routes.draw do

  resources :admin
  resources :accesses
  devise_for :users, controllers: {
        registrations: 'users/registrations'
      }

  root 'welcome#index'

错误：这是我当前的错误：

如果有人有更好的方法或链接来帮助我 - 我最近正在学习 Rails，所以任何阅读都会很好。