gistfile1.py

In [1]: %psource Tiger
class Tiger(models.Model):

    call = models.CharField(max_length=255, blank=True)

In [2]: tony = Tiger()

In [3]: tony.call = u'Grrrreeeeeeeeaaaaaatttt'

In [4]: tony.save()

In [5]: tony.call = None

In [6]: tony.save()
---------------------------------------------------------------------------
IntegrityError                            Traceback (most recent call last)

/home/rob/python/someproject/someproject/<ipython console> in <module>()

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/models/base.pyc in save(self, force_insert, force_update, using)
    454         if force_insert and force_update:
    455             raise ValueError("Cannot force both insert and updating in model saving.")
--> 456         self.save_base(using=using, force_insert=force_insert, force_update=force_update)
    457 
    458     save.alters_data = True

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/models/base.pyc in save_base(self, raw, cls, origin, force_insert, force_update, using)
    520                     if force_update or non_pks:
    521                         values = [(f, None, (raw and getattr(self, f.attname) or f.pre_save(self, False))) for f in non_pks]
--> 522                         rows = manager.using(using).filter(pk=pk_val)._update(values)
    523                         if force_update and not rows:
    524                             raise DatabaseError("Forced update did not affect any rows.")

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/models/query.pyc in _update(self, values)
    495         query.add_update_fields(values)
    496         self._result_cache = None
--> 497         return query.get_compiler(self.db).execute_sql(None)
    498     _update.alters_data = True
    499 

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/models/sql/compiler.pyc in execute_sql(self, result_type)
    864         related queries are not available.
    865         """
--> 866         cursor = super(SQLUpdateCompiler, self).execute_sql(result_type)
    867         rows = cursor and cursor.rowcount or 0
    868         is_empty = cursor is None

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/models/sql/compiler.pyc in execute_sql(self, result_type)
    730 
    731         cursor = self.connection.cursor()
--> 732         cursor.execute(sql, params)
    733 
    734         if not result_type:

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/backends/util.pyc in execute(self, sql, params)
     13         start = time()
     14         try:
---> 15             return self.cursor.execute(sql, params)
     16         finally:
     17             stop = time()

/home/rob/.virtualenvs/animal/lib/python2.6/site-packages/django/db/backends/sqlite3/base.pyc in execute(self, query, params)
    198         query = self.convert_query(query)
    199         try:
--> 200             return Database.Cursor.execute(self, query, params)
    201         except Database.IntegrityError, e:
    202             raise utils.IntegrityError, utils.IntegrityError(*tuple(e)), sys.exc_info()[2]

IntegrityError: animal_tiger.call may not be NULL

In [7]: tony.call = u''

In [8]: tony.save()