How to make email field unique in model User from contrib.auth in Django

Question

I need to patch the standard User model of contrib.auth by ensuring the email field entry is unique:

User._meta.fields[4].unique = True
<         


        

Answer 1

To ensure a User, no matter where, be saved with a unique email, add this to your models:

@receiver(pre_save, sender=User)
def User_pre_save(sender, **kwargs):
    email = kwargs['instance'].email
    username = kwargs['instance'].username

    if not email: raise ValidationError("email required")
    if sender.objects.filter(email=email).exclude(username=username).count(): raise ValidationError("email needs to be unique")

Note that this ensures non-blank email too. However, this doesn't do forms validation as would be appropriated, just raises an exception.