> No, there's quite a difference. "Initial" is used to set the initial
> values and is quite appropriate when a *new* model instance is going to
> be created. The "instance" is used when you want the ModelForm to be
> used to update an existing instance of a model.
> Since Django does not
> currently incorporate mind-reading technology, if the two parameters
> were merged into one, the framework wouldn't know whether it's meant to
> be updating an existing instance or creating a new one.
I don't think this is necessarily the case, and maybe you'll correct
me if I'm wrong. :) Looking at db.models.base.save_base, there is
some checking to see if 1) the pk is set and 2) if the pk exists in
the db when determining whether or not to save or update. And it does
not look as though ModelForm will force_update or force_insert when
calling instance.save().
Still though, couldn't your logic be applied on just an initial
variable. I.e., if initial is a dict, it's an insert. If it's a
model, then we have an update (not that I agree this is the way it
should be). It does however look as though initial values will
override instance values, and I don't see a way to retain this feature
without having both of these arguments. I guess I question how useful
the "initial values override instance values" feature is, because why
not simply change the model before constructing the form?
Anyway, none of this really has to do with my issue, which is that
initial= doesn't appear to set FK drop-downs (or I'm doing it wrong).
Using instance= does set FK drop-downs (even though this is not an
update; I create the model from a dict stored in a session), however I
am have trouble saving the values POSTed from a form created based on
the following sequence:
In a GET:
page_data = self._get_page_data(request.session, page0)
form_class = self.get_form_list(request.session)[page0]
if issubclass(form_class, forms.ModelForm):
form = form_class(instance=form_class.Meta.model(**page_data))
# ... render the form
When this form is POSTed, something like this happens:
if form.is_valid:
request.session[self._get_page_key(page0)] = form.cleaned_data
Basically, I store the cleaned_data in the session for POSTs and use
the cleaned_data in order to initialize a ModelForm for display after
GETs. Eventually, I have to save some things. When that happens, I
again get the data from a session:
for i in range(len(self.get_form_list(request.session))):
page_data = self._get_page_data(request.session, i)
form_class = form_list[i]
form = form_list[i](page_data)
form.save()
At this point, though, I will have trouble with foreign keys again.
Specifically, I have actual ForeignKey model objects in my data
argument, and save throws a TypeError like so:
int() argument must be a string or a number, not 'MyModel'
Thanks for any suggestions,
Dave
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