On Tuesday, April 2, 2019 at 2:12:50 PM UTC-7, Carsten Fuchs wrote:
>
> 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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