class User(AbstractBaseUser):
    USERNAME_FIELD = 'email'


AUTH_USER_MODEL = 'userprofile.User'

但是,如果用他的电子邮件注册的用户(demo@demo.com)和密码尝试使用与同一电子邮件地址关联的Facebook帐户登录,则会收到以下错误：

IntegrityError at /social/complete/facebook/
duplicate key value violates unique constraint "userprofile_user_email_key"
DETAIL:  Key (email)=(demo@demo.com) already exists.

/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/core/handlers/base.py in get_response
                    response = wrapped_callback(request,*callback_args,**callback_kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/views/decorators/csrf.py in wrapped_view
        return view_func(*args,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/apps/django_app/utils.py in wrapper
            return func(request,backend,*args,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/apps/django_app/views.py in complete
                       redirect_name=REDIRECT_FIELD_NAME,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/actions.py in do_complete
                                 *args,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/strategies/base.py in complete
        return self.backend.auth_complete(*args,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/backends/facebook.py in auth_complete
        return self.do_auth(access_token,response,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/backends/facebook.py in do_auth
        return self.strategy.authenticate(*args,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/strategies/django_strategy.py in authenticate
        return authenticate(*args,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/contrib/auth/__init__.py in authenticate
            user = backend.authenticate(**credentials) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/backends/base.py in authenticate
        return self.pipeline(pipeline,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/backends/base.py in pipeline
        out = self.run_pipeline(pipeline,pipeline_index,**kwargs) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/backends/base.py in run_pipeline
            result = func(*args,**out) or {} ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/pipeline/user.py in user_details
            strategy.storage.user.changed(user) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/social/storage/django_orm.py in changed
        user.save() ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/base.py in save
                       force_update=force_update,update_fields=update_fields) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/base.py in save_base
            updated = self._save_table(raw,cls,force_insert,force_update,using,update_fields) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/base.py in _save_table
                                      forced_update) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/base.py in _do_update
        return filtered._update(values) > 0 ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/query.py in _update
        return query.get_compiler(self.db).execute_sql(None) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/sql/compiler.py in execute_sql
        cursor = super(sqlUpdateCompiler,self).execute_sql(result_type) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/models/sql/compiler.py in execute_sql
        cursor.execute(sql,params) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/debug_toolbar/panels/sql/tracking.py in execute
        return self._record(self.cursor.execute,sql,params) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/debug_toolbar/panels/sql/tracking.py in _record
            return method(sql,params) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/backends/util.py in execute
            return super(CursorDebugWrapper,self).execute(sql,params) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/backends/util.py in execute
                return self.cursor.execute(sql,params) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/utils.py in __exit__
                six.reraise(dj_exc_type,dj_exc_value,traceback) ...
/Users/vera/.virtualenvs/app/lib/python2.7/site-packages/django/db/backends/util.py in execute
                return self.cursor.execute(sql,params) ...

当有人注册他的Facebook帐户,然后登录一切正常.当他注册他的电子邮件时我会出现问题(我正在使用django-registration),因此我们有一个User(但不是UserSocialAuth)实例,然后我们尝试使用与他相同的电子邮件地址关联的Facebook帐户登录.