Confused about uploading files (Cannot force both insert and updating in model saving)

[Roy Smith]

I'm trying to figure out how to upload a file.  I've got a model that
looks like:

class DataSet(models.Model):
    file = models.FileField(upload_to='data/%Y/%m/%d')

and my view method is:

def create_data_set(request):
    if request.method == 'POST':
        form = DataSetForm(request.POST,
                           request.FILES)
        if form.is_valid():
            f = request.FILES['file']
            data_set = DataSet()
            data_set.save('foo', f)
            return HttpResponseRedirect("/")
        print "invalid"
    else:
        form = DataSetForm()
    ctx = {'form': form}
    ctx.update(csrf(request))
    return render_to_response('chart/data_set.html', ctx)

with a form....

class DataSetForm(forms.Form):
    file = forms.FileField()

When I execute this, I get a form containing a file picker (so far, so
good), but when I submit the form I get a mysterious error (below).
What am I doing wrong?


Environment:


Request Method: POST
Request URL: http://localhost:8000/dataset/create

Django Version: 1.3
Python Version: 2.6.1
Installed Applications:
['django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'chart']
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 "/Users/roy/lib/webchart/lib/python2.6/site-packages/Django-1.3-
py2.6.egg/django/core/handlers/base.py" in get_response
  111.                         response = callback(request,
*callback_args, **callback_kwargs)
File "/Users/roy/WebChart/chart/views.py" in create_data_set
  27.             data_set.save('foo', f, False)
File "/Users/roy/lib/webchart/lib/python2.6/site-packages/Django-1.3-
py2.6.egg/django/db/models/base.py" in save
  459.             raise ValueError("Cannot force both insert and
updating in model saving.")

Exception Type: ValueError at /dataset/create
Exception Value: Cannot force both insert and updating in model
saving.

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