Expected a character buffer object

Question

Models in this post. In admin.py:

class GroupsAdmin(admin.ModelAdmin):

    fieldsets = [
        (None,               {'fields': ['first_year', 'many other']}),

    ]

So, in this admin section I can add first_year to the special series of cars. I press "+", then opens a new window - where I can add the year. I add '2011', press "Save" and see the error:

TypeError: expected a character buffer object.

Its very strange, because it works at last week. How it fix? If I go to the first_yearAdmin, and add the year, it works without errors.

Thanks.

Edit. Traceback:

Environment:


Request Method: POST
Request URL: http://127.0.0.1:8000/admin/cars/first_year/add/?_popup=1

Django Version: 1.5
Python Version: 2.7.3
Installed Applications:
('django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'django.contrib.sitemaps',
 'cars',
 'django_evolution',
 'django.contrib.admin')
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware')


Traceback:
File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  115.                         response = callback(request, *callback_args, **callback_kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in wrapper
  372.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  91.                     response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/views/decorators/cache.py" in _wrapped_view_func
  89.         response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/sites.py" in inner
  202.             return view(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapper
  25.             return bound_func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  91.                     response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in bound_func
  21.                 return func(self, *args2, **kwargs2)
File "/usr/local/lib/python2.7/dist-packages/django/db/transaction.py" in inner
  223.                 return func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in add_view
  1010.                 return self.response_add(request, new_object)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in response_add
  833.                 (escape(pk_value), escapejs(obj)))
File "/usr/local/lib/python2.7/dist-packages/django/utils/functional.py" in wrapper
  194.             return func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/html.py" in escapejs
  65.     return mark_safe(force_text(value).translate(_js_escapes))

Exception Type: TypeError at /admin/cars/first_year/add/
Exception Value: expected a character buffer object

Models

class Mark(models.Model):
    many_many_char_fields
    def __unicode__(self):
        return self.name

class First_Year(models.Model):
    year = models.IntegerField()
    def __unicode__(self):
        return str(self.year)

class Groups(models.Model):
        many_other_fields
    mark = models.ForeignKey(Mark, related_name='groups')
    last_update = models.DateTimeField()
    first_year = models.ForeignKey(First_Year, related_name='first_year')
    def __unicode__(self):
        return self.name
    def altered_date(self, year):
        altered_year = int(year)-int(self.first_year.year)
        return altered_year

Answer 1

Actually, it is not necessary to transform the year field into Charfield, if you want to keep it Integer, as it would be impossible in many cases where you really need a number. The workaround for this 1.5 bug is to make __unicode__ function return unicode string:

class First_Year(models.Model):
    year = models.IntegerField()

    def __unicode__(self):
        return unicode(self.year)