In django inline model admin, how to prefill extra fields with values

Question

class MyCustomInline(admin.TabularInline):
    min_num = 1
    extra = 0
    fields = ['matcher', 'param0', 'param1']
    model = MyModel
    form = MyCustomInlineForm

   def get_formset(self, request, obj=None, **kwargs):
        extra_fields = {
            'param0': forms.CharField(label='First Param', required=False),
            'param1': forms.CharField(label='Second Param', required=False)
        }
        kwargs['form'] = type('MyCustomInline', (MyCustomInlineForm,), extra_fields)
        return super(MyCustomInline, self).get_formset(request, obj, **kwargs)

This is basically how I define my inline form so that it has two extra fields - matcher is a standard field in the related table and the inline form handles it automatically. And I save the extra param values in a different storage via overriding the save() in MyCustomInlineForm .

But if I edit an existing record - matcher value appears correctly but I obviously also want to preload the param0 and param1 with the corresponding values. Where can I hook up to do that?

Answer 1

I managed to do it on my own. I also managed to simplify the way I define my custom extra fields, without overriding get_formset method:

class MyCustomInlineForm(forms.ModelForm):
    matcher = forms.ChoiceField(choices=[(v['name'], v['name']) for v in matchers], label='Matcher')
    param0 = forms.CharField(label='First Param', required=False)
    param1 = forms.CharField(label='Second Param', required=False)

    def __init__(self, *args, **kwargs):
        super(MyCustomInlineForm, self).__init__(*args, **kwargs)
        if self.instance.pk:
            """ self.instance is the model for the current row.
                If there is a pk property that is not None, it means it's not
                a new, empty inline model but we are working with existing one."""
            self.initial['param0'], self.initial['param1'] = custom_way_to_load_params(self.instance)

    def save(self, commit=True):
        model = super(MyCustomInlineForm, self).save(True)
        param0 = self.cleaned_data['param0']
        param1 = self.cleaned_data['param1']
        custom_way_to_save_params(model, param0, param1)
        return model



class MyCustomInline(admin.TabularInline):
    min_num = 1
    extra = 0
    fields = ['matcher', 'param0', 'param1']
    model = MyModel
    form = MyCustomInlineForm

If needed - validation of custom params could be done by overriding is_valid() method of forms.ModelForm class and adding errors via self.add_error() . I hope it helps someone.