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.
> On May 6, 2016, at 9:22 AM, Michel Z. Santello <michel...@gmail.com> wrote:
>
> Can somebody explain why did occurs with widget=forms.HiddenInput ?
>
> Thank's.
>
>
>
>
> Em quarta-feira, 31 de março de 2010 10:20:48 UTC-3, Phoebe Bright escreveu:
> 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????
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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