modelform fails is_valid w/o setting form.errors - django

Question

I'm using a modelform to display only a subset of the fields in the model. When the form is submitted it fails form.is_valid() but form.errors is empty. I'd rather not display all my code here, but below is a sample:
Model and Form
class Videofiles(models.Model):
active = models.CharField(max_length=9)
filenamebase = models.CharField(max_length=180, primary_key=True, db_column='FilenameBase')
program = models.CharField(max_length=60, db_column='Program')
displayname = models.CharField(max_length=150, db_column='DisplayName')
description = models.TextField(db_column='Description', blank=True)
tagskeywords = models.TextField(db_column='TagsKeywords', blank=True)
class Meta:
db_table = u'legacyTable'
class VideoFilesForm(ModelForm):
filenamebase = forms.CharField(max_length=30)
displayname = forms.CharField(max_length=30)
description = forms.CharField(max_length=30, required=False)
tagskeywords = forms.CharField(max_length=60, required=False)
class Meta:
model=Videofiles
fields=['filenamebase','displayname','description','tagskeywords']
View
def editClip(request, clipId):
clip = Videofiles.objects.get(filenamebase=clipId)
form = VideoFilesForm(instance=clip)
if request.method == 'POST':
if 'save' in request.POST:
if form.is_valid():
form.save()
else:
print form.errors
return render_to_response('legacyDB/edit_clip.html',locals())

Answer 1

Your form is unbound, because you are not passing any data to it. Calling is_valid on an unbound form will always return False, with empty errors (see the form api docs).
Your view should be something like the following:
def editClip(request, clipId):
clip = Videofiles.objects.get(filenamebase=clipId)
if request.method == 'POST':
# create bound form with input from request.POST
form = VideoFilesForm(request.POST, instance=clip)
if 'save' in request.POST:
if form.is_valid():
form.save()
else:
print form.errors
else:
# create unbound form to display in template
form = VideoFilesForm(instance=clip)
return render_to_response('legacyDB/edit_clip.html',locals())