how can I change an OneToOne field in django Custom User?

Question

I have a OneToOne relationship in my CustomUser model. my model is:

class Channel(models.Model):
    channel_name = models.CharField(max_length=60, primary_key=True)
    channel_host = models.CharField(max_length=60)
    channel_secret = models.CharField(max_length=60)
    profile_type = models.ForeignKey(Profile)
    channel_register_time = models.DateField(auto_now_add=True)
    channel_creator = models.CharField(max_length=60)

class CustomUser(AbstractUser):
    channel = models.OneToOneField(Channel, unique=True, db_index=True, primary_key=True)
    register_time = models.DateField(auto_now_add=True)
    cellphone = models.CharField(max_length=60)
    fax = models.CharField(max_length=60)
    tell = models.CharField(max_length=60)
    picture = models.ImageField(upload_to='media/', max_length=100) 

when I create a new user every thing is fine, but when I try to change the channl field I get this error:

In [93]: c1 = Channel.objects.create(channel_name='channel1',profile_type=p)

In [94]: c2 = Channel.objects.create(channel_name='channel2',profile_type=p)

In [95]: u = CustomUser.objects.create(username='django',channel=c1)

In [96]: u.channel = c2

In [97]: u.save()
---------------------------------------------------------------------------
IntegrityError                            Traceback (most recent call last)
<ipython-input-97-5d13c143bca2> in <module>()
----> 1 u.save()

/usr/lib/python2.7/site-packages/django/db/models/base.pyc in save(self, force_insert, force_update, using, update_fields)
    543 
    544         self.save_base(using=using, force_insert=force_insert,
--> 545                        force_update=force_update, update_fields=update_fields)
    546     save.alters_data = True
    547 

/usr/lib/python2.7/site-packages/django/db/models/base.pyc in save_base(self, raw, force_insert, force_update, using, update_fields)
    571             if not raw:
    572                 self._save_parents(cls, using, update_fields)
--> 573             updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
    574         # Store the database on which the object was saved
    575         self._state.db = using

/usr/lib/python2.7/site-packages/django/db/models/base.pyc in _save_table(self, raw, cls, force_insert, force_update, using, update_fields)
    652 
    653             update_pk = bool(meta.has_auto_field and not pk_set)
--> 654             result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
    655             if update_pk:
    656                 setattr(self, meta.pk.attname, result)

/usr/lib/python2.7/site-packages/django/db/models/base.pyc in _do_insert(self, manager, using, fields, update_pk, raw)
    685         """
    686         return manager._insert([self], fields=fields, return_id=update_pk,
--> 687                                using=using, raw=raw)
    688 
    689     def delete(self, using=None):

/usr/lib/python2.7/site-packages/django/db/models/manager.pyc in _insert(self, objs, fields, **kwargs)
    230 
    231     def _insert(self, objs, fields, **kwargs):
--> 232         return insert_query(self.model, objs, fields, **kwargs)
    233 
    234     def _update(self, values, **kwargs):

/usr/lib/python2.7/site-packages/django/db/models/query.pyc in insert_query(model, objs, fields, return_id, raw, using)
   1509     query = sql.InsertQuery(model)
   1510     query.insert_values(fields, objs, raw=raw)
-> 1511     return query.get_compiler(using=using).execute_sql(return_id)
   1512 
   1513 

/usr/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in execute_sql(self, return_id)
    896         cursor = self.connection.cursor()
    897         for sql, params in self.as_sql():
--> 898             cursor.execute(sql, params)
    899         if not (return_id and cursor):
    900             return

/usr/lib/python2.7/site-packages/django/db/backends/util.pyc in execute(self, sql, params)
     67         start = time()
     68         try:
---> 69             return super(CursorDebugWrapper, self).execute(sql, params)
     70         finally:
     71             stop = time()

/usr/lib/python2.7/site-packages/django/db/backends/util.pyc in execute(self, sql, params)
     51                 return self.cursor.execute(sql)
     52             else:
---> 53                 return self.cursor.execute(sql, params)
     54 
     55     def executemany(self, sql, param_list):

/usr/lib/python2.7/site-packages/django/db/utils.pyc in __exit__(self, exc_type, exc_value, traceback)
     97                 if dj_exc_type not in (DataError, IntegrityError):
     98                     self.wrapper.errors_occurred = True
---> 99                 six.reraise(dj_exc_type, dj_exc_value, traceback)
    100 
    101     def __call__(self, func):

/usr/lib/python2.7/site-packages/django/db/backends/util.pyc in execute(self, sql, params)
     51                 return self.cursor.execute(sql)
     52             else:
---> 53                 return self.cursor.execute(sql, params)
     54 
     55     def executemany(self, sql, param_list):

/usr/lib/python2.7/site-packages/django/db/backends/sqlite3/base.pyc in execute(self, query, params)
    448             return Database.Cursor.execute(self, query)
    449         query = self.convert_query(query)
--> 450         return Database.Cursor.execute(self, query, params)
    451 
    452     def executemany(self, query, param_list):

IntegrityError: column username is not unique

am I missed some thing? how can I change my channel field?

Answer 1

It's because the channel field on your CustomUser model has primary_key=True.

This means when you do:

In [96]: u.channel = c2

In [97]: u.save()

...you have changed the primary key of u, therefore when you save it is creating a new user, but with the same username as the original one, hence the IntegrityError.

I think you need to do it like this instead:

u = CustomUser.objects.get(username='django')
u.delete()
u.channel = c2
u.save()