populating prefixed fields - bug or feature? - django

Question

Having the following models:
#models.py
Column(models.Model):
name = models.CharField()
Input(models.Model):
column = ForeignKey(Column)
text = models.CharField()
And the following form:
class InputForm(Modelform):
class Meta():
model=Input
The following works:
c = Column.objects.get(...)
i=InputForm({'column':c.id})
i.is_valid() #true
In my application I am generating many forms, to avoid clashes I prefix it:
i=InputForm({'column':c.id}, prefix=prfx()) #prfx() is dynamically generated
i.errors # ({'column':['This field is required']})
i.data['column'] is still the right value
I also tried:
i.column = c
i.errors # ({'column':['This field is required']})
How do I populate the column field?
I cannot save the form as long as it does not validate
EDIT What I am trying to achieve:
I am building dynamic forms:
form_list = [InputForm(column, prefix=column.id) for column in col_list]
In the template I iterate over this form list (and I want to set the column field to be invisible.
{% for form in form_list %}
{{form.as_ul}}
{%endfor%}
This form then shall be processed by an AjaxView. The relation between text and column is achieved by the invisible field.

Answer 1

The first parameter to the form is the input data, which is usually request.POST. If you render a Form with a prefix, you will see that all form html elements will have a prefixed name, for example <input name='yourprefix_text' /> etc. If you POST such a form to your Django app, the POSTed data will have the prefix, too.
So, if you are using a prefix, the input data needs to be prefixed, too:
f = InputForm({'yourprefix_column': c.id}, prefix='yourprefix')
Usually, it is a better idea to use the initial parameter to the form for default values, because otherwise the form is always bound, and this has some consequences, for example default/initial values for other fields are will not work.
f = InputForm(prefix='yourprefix', initial={'column': c})
# or ...
form_list = [InputForm(prefix=column.id, initial={'column': column})
for column in col_list]
If you want to always set the column to a programatically determined value, and not allow the user to change it, it is better to not include the field in your form, and set the field manually after saving the object:
f = InputForm(request.POST)
if f.is_valid():
instance = f.save(commit=False)
instance.column = c
instance.save()
To make your field hidden, you can change the widget, as described in the documentation:
class InputForm(ModelForm):
class Meta:
widgets = {
'column': forms.HiddenInput,
}
# ...