title: Django - How do I use UserChangeForm my in web-app?
body: <p>When I tried to modify the current entry with UserChangeForm in my page, it says "User is already existed". But the I had no problem modifying the entry through the admin portal.</p>
  
  <p>model.py</p>
  
  <pre><code>class User(AbstractUser):
      users = (
          ('doctor', 'Doctor'),
          ('patient', 'Patient'),
          ('assistant', 'Assistant'),
      )
  
      user_type = models.CharField(choices=users, max_length=9, default='patient')
  
      #return the users' name
      def __str__(self):
          return self.first_name  + " " + self.last_name
  
  class Doctor(models.Model):
      upin = models.AutoField(primary_key=True) #unique physician identification number
      user = models.OneToOneField(User, on_delete=models.CASCADE)
      user.user_type = "doctor"
      specialty = models.CharField(max_length=20)
      appointments_per_hour = models.IntegerField(null=True)
  
      #return the doctors' name
      def __str__(self):
          return str(self.user)
  </code></pre>
  
  <p>forms.py</p>
  
  <pre><code>class DoctorForm(UserChangeForm):
      class Meta:
          model = Doctor
          fields = ('user','specialty','appointments_per_hour',)
  </code></pre>