title: django.core.exceptions.FieldError: Unknown field(s) (username) specified for Employee
body: <p>I am trying to extend the user model</p>
  
  <p>so I created a new model called employee with foreignkey to user model</p>
  
  <pre><code>from django.db import models
  
  from django.contrib.auth.models import User
  
  class Employee(models.Model):
      user = models.OneToOneField(User, on_delete=models.CASCADE)
      department = models.CharField(max_length=200)
  </code></pre>
  
  <p>and tried to create a form for the signup</p>
  
  <pre><code>from django.contrib.auth.forms import UserCreationForm
  from employee.models import Employee
  
  class EmployeeForm(UserCreationForm):
      class Meta(UserCreationForm.Meta):
          model = Employee
          fields = UserCreationForm.Meta.fields + ('department',)
  </code></pre>
  
  <p>These are the only changes I made I am getting the following error:</p>
  
  <blockquote>
    <p>File "/home/sugumar/python/django/project1/project1/urls.py", line
    18, in 
        from employee.views import signup   File "/home/sugumar/python/django/project1/employee/views.py", line 2, in
    
        from .forms import EmployeeForm   File "/home/sugumar/python/django/project1/employee/forms.py", line 4, in
    
        class EmployeeForm(UserCreationForm):   File "/home/sugumar/.local/share/virtualenvs/project1-j0yhUYNK/lib/python3.5/site-packages/django/forms/models.py",
    line 266, in <strong>new</strong>
        raise FieldError(message) django.core.exceptions.FieldError: Unknown field(s) (username) specified for Employee</p>
  </blockquote>