[Answered ]-Django: Using prefetch_selected with get() and filter()

You chained them in the wrong order, do it this way:

Project.objects.select_related('funders').get(id=project_id)

and

Project.objects.select_related('funders').filter(id__in=[‘list-of-ids])

You have to call select_related and prefetch_related on the Manager object (Project.objects).

select_related() is a queryset method. The documentation on querysets has two sections of methods: methods that return a new queryset, and methods that do not return a queryset. get() is in the second section, so you can’t chain any other queryset methods after it.

One other thing: prefetch_related() runs an extra query for each model. Since you’re only fetching a single project, project.funders.all() will run exactly 1 query to fetch all related organizations regardless of your use of prefetch_related(). prefetch_related becomes useful when you need the related organizations for multiple projects.

Since funder is m2m you cannot use select_related, you have to us prefetch instead. select_related only work on foreign key and one to one relation

Project.objects.prefetch_related('funders').filter(id__in=[id1, id2])