Passing hidden foreign key to form as initial value

[phoebebright]

Displayed fields resolve as expected, hidden fields cause errors.

This works:

in the model
CourseBook has a foreign key to Course

In the view:

course = Course.objects.get(pk=whatever)
form = CouseBook(initial = {'course': course})

in the Form:

class CourseBook(ModelForm):
class Meta:
model = CourseBooking

The web page now displays a picklist of courses with the initial value
highlighted. I can now do a form.save() no problem.

However, if I make the course a hidden field, which is what I want.

class CourseBook(ModelForm):
course = forms.CharField(widget=forms.HiddenInput())

class Meta:
model = CourseBooking

then when I come to save() I get a ValueError, unable to assign "My
course" etc. as it tries to put the name of the course into the
foreign key instead of a course instance.

I can work around this putting a save method on the form, but it seems
to me django should resolve this for me????

[Brandon Taylor]

Hi there,

Instead of using the course object in your initial data, which will
pass in the __unicode__ representation of the object, pass in the id:

form = CouseBook(initial = {'course': course.id})

That should get you the numeric id, but you'll also need to override
your save method to get the course object to assign when you save your
CourseBook form, as you can't assign an integer (coming from your
hidden form field) to the value of a ForeignKey field on a model.

HTH,
Brandon

[phoebebright]

Brandon, Thanks for your suggestion.
I tried passing it an ID, but as you say, I also have to override the
save. What I don't understand is why it does it fine if the form
includes the foreign key in a popup? They are both passing back
integers after all.

Also failed to get the save method working, tried to pass in the
course instance, but it still ends up trying to save with the id of
the course. Is it not using cleaned_data?

def save(self, course=False, force_insert=False,
force_update=False, commit=True):
if course:
self.cleaned_data['course'] = course
return super(CourseBook, self).save(commit=commit)

Any suggestions welcome as I've spent the whole afternoon on this - I
won't go through the many other workarounds that havn't worked!

Phoebe.

[phoebebright]

Final approach:
in the forms.py excluded the courses foreign key field
in models.py made courses blank and nullable
didn't pass any initial values to the form
in the view, saved the form like this:
item = Courses.objects.get(pk=whatever)
obj = form.save(commit=False)
obj.course = item
obj.save()

This doesn't feel very tidy to me, I think the form should have the
hidden values, but it works!

[Nuno Maltez]

What about:

class CourseBook(ModelForm):
course = ModelChoiceField(queryset=Course.objects.all(),
widget=HiddenInput())

class Meta:
model = CourseBooking

and in your view:

form = CourseBook(initial = {'course': course.pk})

Nuno

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[phoebebright]

That's one option, the problem is changing the course value returned
from the form into a course object so that the form will validate.
This turned out to be a surprising amount of trouble (because you have
to do it before validation), hence reason for doing simpler work
around.

On Apr 1, 2:08 pm, Nuno Maltez <nuno.li...@gmail.com> wrote:
> What about:
>
> class CourseBook(ModelForm):
>    course = ModelChoiceField(queryset=Course.objects.all(),
> widget=HiddenInput())
>
>    class Meta:
>        model = CourseBooking
>
> and in your view:
>
> form = CourseBook(initial = {'course': course.pk})
>
> Nuno
>

> On Wed, Mar 31, 2010 at 8:06 PM, phoebebright <phoebebright...@gmail.com> wrote:
> > Final approach:
> > in the forms.py excluded the courses foreign key field
> > in models.py made courses blank and nullable
> > didn't pass any initial values to the form
> > in the view, saved the form like this:
> >            item = Courses.objects.get(pk=whatever)
> >            obj = form.save(commit=False)
> >            obj.course = item
> >            obj.save()
>
> > This doesn't feel very tidy to me, I think the form should have the

> >hiddenvalues, but it works!

> >> >hiddenform field) to the value of a ForeignKey field on a model.

>
> >> > HTH,
> >> > Brandon
>
> >> > On Mar 31, 8:20 am, phoebebright <phoebebright...@gmail.com> wrote:
>

> >> > > Displayed fields resolve as expected,hiddenfields cause errors.

>
> >> > > This works:
>
> >> > > in the model
> >> > > CourseBook has a foreign key to Course
>
> >> > > In the view:
>
> >> > > course = Course.objects.get(pk=whatever)
> >> > > form = CouseBook(initial = {'course': course})
>
> >> > > in the Form:
>
> >> > > class CourseBook(ModelForm):
> >> > >     class Meta:
> >> > >         model = CourseBooking
>
> >> > > The web page now displays a picklist of courses with the initial value
> >> > > highlighted.  I can now do a form.save() no problem.
>

> >> > > However, if I make the course ahiddenfield, which is what I want.

[Nuno Maltez]

I think the form I sent, with ModelChoiceField, will validate with the
returned values without any further code. Or am I missing something
obvious?

[phoebebright]

OK - Now I've actually read your code properly! Yes that is a
brilliant solution!

Thanks.

Phoebe.

On Apr 1, 7:01 pm, Nuno Maltez <nuno.li...@gmail.com> wrote:
> I think the form I sent, with ModelChoiceField, will validate with the
> returned values without any further code. Or am I missing something
> obvious?
>

[Michel Z. Santello]

Can somebody explain why did occurs with widget=forms.HiddenInput ?

Thank's.

[Peter of the Norse]

Because CharField is designed for text data. So the form field turns the course into a string and tries to save a string to the model. That doesn’t work.

The only built-in field designed to work with foreign keys is ModelChoiceField. You could update it so that it doesn’t run a queryset and uses HiddenInput.

The other option is to remove course from the ModelForm and instead use course_id with IntergerField. This would be the fastest and not hit the database as often. I recommend doing this. Or, if this uses an existing object, not have anything there. Things left out of the ModelForm don’t get updated when you save the form.

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Peter of the Norse
Rahm...@Radio1190.org