Support of object_list in ModelChoiceField and ModelMultipleChoiceField

[Sven R. Kunze]

We encountered the need of having object_list (list of model instances) instead of a queryset several times when initializing a ModelChoiceField or ModelMultipleChoiceField.

Is there some chance of getting this implemented?

[Tim Graham]

I seem to remember this being discussed before but am not finding anything right away. Is there a problem converting a list of instances to a queryset using something like queryset=Model.objects.filter(pk__in=[x.pk for x in object_list])?

[Tim Graham]

I'm probably remembering #23672 (marked as wontfix) which proposes similar functionality for BaseModelFormset.

[Sven R. Kunze]

Sure, recreating a queryset from the object list is also our current approach.

We could identify two issues so far:
1) code duplication (already observed)
2) performance

Number 2) worries me most as we observed performance issues recently. So, this only contributes further.

Perhaps it would help when I explain our use-case.

We designed tree widgets for both choice and multiple choice fields. They work quite well when all items can be expressed easily on terms a regular queryset. However, as you can imagine, tree data enables some pretty interesting and complex use-cases. So, the object list is built differently here.

Currently, we cheat by using the ModelChoiceIterator as it exposes the original queryset to the widget.

[Tim Graham]

Have you considered a custom field instead? Looking at the code of the fields you mentioned, it doesn't look to me like a dual purpose implementation that allows either a queryset or a list of instances would be simple. As to whether or not such a field should be included in Django itself, I'd suggest to write to the DevelopersMailingList to get feedback on it if you have some code to show. Thanks!