Ruby rails - undefined method `model_name' for NilClass:Class

Question

I am trying to make a small search form to search a user in ldap. It doesn't really have anything to do with local data model. Not sure why do I need any changes in the user controller. The error is not giving any clue to me.

Model - function to search in ldap

class User < ActiveRecord::Base
  attr_accessible :user_id, :firstname, :lastname, :email, :role, :misc, :password

  validates_presence_of :user_id, :firstname, :lastname, :email, :role, :on => :create
  validates_uniqueness_of :user_id, :email

  ROLES = ['Admin','User']

####################
  SERVER = '10.10.10.1'   
  PORT = 389                    
  BASE = 'DC=User,DC=mysite,DC=com'   
  DOMAIN = 'ldap.mysite.com'       
####################

  def self.ActiveDirectoryAuthenticate(login, pass)
     user = find_by_user_id(login)

     if user
     nil
     else
     return false
     end
        conn = Net::LDAP.new :host => SERVER,
                         :port => PORT,
                         :base => BASE,
                         :auth => { :username => "#{login}@#{DOMAIN}",
                                    :password => pass,
                                    :method => :simple }
        if conn.bind
        return user
        else
        return false
        end
        rescue Net::LDAP::LdapError => e
        return false
end

  def self.findActiveDirectory(login)
        conn = Net::LDAP.new :host => SERVER,
                         :port => PORT,
                         :base => BASE,
                         :auth => { :username => 'admin',
                                    :password => 'adminpass',
                                    :method => :simple }

if  conn.bind
        conn.search(:base => BASE, :filter => Net::LDAP::Filter.eq( "sAMAccountName", login ),
        :attributes => ['givenName','SN','mail'], :return_result => true) do |entry|
        entry.each do |attributes, values|

        if "#{attributes}" == "sn"
        values.each do |value|
        puts "Lastname: "+"#{value}"
        $lastname = "#{value}"
        end
        end

        if "#{attributes}" == "givenname"
        values.each do |value|
        puts "Firstname: "+"#{value}"
        $firstname = "#{value}"
        end
        end

        if "#{attributes}" == "mail"
        values.each do |value|
        puts "Email: "+"#{value}"
        $email = "#{value}"
        end
        end

        end
        end

    return true
    else
    return false
    end

    rescue Net::LDAP::LdapError => e
    return false
   end

end

User controller -

class UsersController < ApplicationController
  def new
    @user = User.new
  end

  def create
    @user = User.new(params[:user])
    if @user.save
      redirect_to users_added_url, :notice => "Signed up!"
    else
      render "new"
    end
  end
end

View - is NOT working (app/views/users/find.html.erb)

<h1>Find User</h1>

<%= form_for @user do |f| %>
  <% if @user.errors.any? %>
    <div class="error_messages">
      <h2>Form is invalid</h2>
      <ul>
        <% for message in @user.errors.full_messages %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>
  <p>
    <%= f.label :Username %><br />
    <%= f.text_field :username %>
  </p>
  <p class="button"><%= f.submit %></p>
<% end %>

View - is working (app/views/users/new.html.erb)

<h1>Add new user</h1>

<%= form_for @user do |f| %>
  <% if @user.errors.any? %>
    <div class="error_messages">
      <h2>Form is invalid</h2>
      <ul>
        <% for message in @user.errors.full_messages %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>
 <p>
    <%= f.label :Username %><br />
    <%= f.text_field :user_id %>
  </p>
 <p>
    <%= f.label :Firstname %><br />
    <%= f.text_field :firstname %>
  </p>
 <p>
    <%= f.label :Lastname %><br />
    <%= f.text_field :lastname %>
  </p>
  <p>
    <%= f.label :Email %><br />
    <%= f.text_field :email %>
  </p>
  <p>
    <%= f.label :Role %><br />
    <%= f.collection_select :role, User::ROLES, :to_s, :to_s, :include_blank => false %>
  </p>
  <p class="button"><%= f.submit %></p>
<% end %>

routes -

# rake routes
  myapp_new GET    /myapp/new(.:format)          myapp#new
        root        /                            home#index
sessions_new GET    /sessions/new(.:format)      sessions#new
   users_new GET    /users/new(.:format)         users#new
 users_added GET    /users/added(.:format)       users#added
      myapp GET    /myapp(.:format)              myapp#new
     log_out GET    /log_out(.:format)           sessions#destroy
      log_in GET    /log_in(.:format)            sessions#new
     sign_up GET    /sign_up(.:format)           users#new
  users_find GET    /users/find(.:format)        users#find
        root        /                            users#new
       users GET    /users(.:format)             users#index
             POST   /users(.:format)             users#create
    new_user GET    /users/new(.:format)         users#new
   edit_user GET    /users/:id/edit(.:format)    users#edit
        user GET    /users/:id(.:format)         users#show
             PUT    /users/:id(.:format)         users#update
             DELETE /users/:id(.:format)         users#destroy
    sessions GET    /sessions(.:format)          sessions#index
             POST   /sessions(.:format)          sessions#create
 new_session GET    /sessions/new(.:format)      sessions#new
edit_session GET    /sessions/:id/edit(.:format) sessions#edit
     session GET    /sessions/:id(.:format)      sessions#show
             PUT    /sessions/:id(.:format)      sessions#update
             DELETE /sessions/:id(.:format)      sessions#destroy

Error -

undefined method `model_name' for NilClass:Class

Answer 1

The problem is that you are using @user in your view, but @user is defined nowhere and thus nil. That's why you get this error:

undefined method `model_name' for NilClass:Class

To solve this you have to add the following to your controller:

def find
  @user = User.new
end

Or change your view like this:

<%= form_for User.new do |f| %>

This will get rid of the error you are getting, but submitting this form will post to your create action, which is not what you want. For searching you'd better use form_tag. Check out Rails Guides for form basics. Basically form_for is for creating and updating data, which does not apply to searching.