我有这个字段的形式:
city = forms.ModelChoiceField(label="city", queryset=MyCity.objects.all())
district = forms.ModelChoiceField(label="district", queryset=MyDistrict.objects.all())
area = forms.ModelChoiceField(label="area", queryset=MyArea.objects.all())
District来自点击的city, area来自点击的area。使用queryset=MyArea.objects.all()和queryset=MyArea.objects.all()表单会非常重。我如何使查询集默认为空?