Dear Django group,
I would like to show users a form that they can use to customize the view, for
example a ChoiceField from which the year of the report can be chosen. It seems
straightforward to use a forms.Form to handle the request.GET data:
from django import forms
class JahrAuswahl(forms.Form):
year = forms.ChoiceField(required=False, choices=[(j, j) for j in
range(2018, 2021)])
def clean_year(self):
y = self.cleaned_data['year']
if not y:
# Set a "default" value here.
y = 2019
print('Year:', y)
return y
However, the problem is with default values. Please consider this:
>>> year_form = JahrAuswahl({'year': 2018}) # Provide explicit data.
>>> print(year_form)
Year: 2018 # from JahrAuswahl.clean_year()
<tr><th><label for="id_year">Year:</label></th><td><select name="year"
id="id_year">
<option value="2018" selected>2018</option> # Just as expected!
<option value="2019">2019</option>
<option value="2020">2020</option>
</select></td></tr>
>>> year_form = JahrAuswahl({}) # Data is empty now, need default values!
>>> print(year_form)
Year: 2019 # JahrAuswahl.clean_year() provides a default value.
<tr><th><label for="id_year">Year:</label></th><td><select name="year"
id="id_year">
<option value="2018">2018</option>
<option value="2019">2019</option> # BUT it doesn't make it back into
year_form.data !
<option value="2020">2020</option>
</select></td></tr>
Well, the problem is that with {} (that is, request.GET == {}), we get default
values in year_form.cleaned_data, but we cannot use year_form in the template
context to render the form fields.
Some work-around might be to use the year_form.cleaned_data to initialize a new
JahrAuswahl instance:
>>> year_form = JahrAuswahl(year_form.cleaned_data) # HACK!?
>>> print(year_form)
Year: 2019
<tr><th><label for="id_year">Year:</label></th><td><select name="year"
id="id_year">
<option value="2018">2018</option>
<option value="2019" selected>2019</option> # ok!
<option value="2020">2020</option>
</select></td></tr>
But this feels like a hack and really not like the proper way to do this.
How can I solve this problem in an elegant Django manner?
Best regards,
Carsten
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