class OperationCategoryOnlyForm(forms.ModelForm):
    class Meta:
      model = Operation
      fields = ('operation_type', 'category', 'related_account', )
      ordering = ['date']


OperationFormSet = modelformset_factory(Operation, form=OperationCategoryOnlyForm)

class Operation(models.Model):
    # field definitions
    class Meta:
        ordering = ('date',)

OperationFormSet = modelformset_factory(Operation, form=OperationCategoryOnlyForm, queryset=Operation.objects.order_by('date'))