如何使用Django的更新视图来检查电子邮件是否唯一？

class UpdateProfile(UpdateView):
    model = User
    fields = ['first_name', 'last_name', 'username', 'email']
    template_name = 'account/update.html'
    success_url = '/accounts/profile/'

    def get_object(self, queryset=None):
        return self.request.user

    def clean_email(self):
        email = self.cleaned_data.get('email')
        username = self.cleaned_data.get('username')
        if email and User.objects.filter(email=email).exclude(username=username).count() > 0:
            raise forms.ValidationError(u'This email address is already registered.')
        return email
class UpdateProfile(UpdateView):
    model = Us