python - Limit the queryset of entries displayed for a django admin Inline

Question

In django admin, using django 1.2, i'm trying to add a InlineModelAdmin to apply a comment on save when a change is made to an entry. (An entry is expected to have a "ChangeComment" for every edit).

I don't want to show previous entries, so I am trying to force the ChangeCommentInline's formset.queryset to be empty, by creating NoCommentsInlineFormset and assigning the formset in my ChangeCommentInline, but is still returning existing entries.

https://docs.djangoproject.com/en/1.3/topics/forms/modelforms/#changing-the-queryset

Note - In the link above they use BaseModelFormset, I'm using BaseInlineFormset, which I expect may be the issue. If I swap out BaseInlineFormset with BaseModelFormset I get an error about "instance" not existing.

admin.py

class NoCommentsInlineFormset(models.BaseInlineFormset):
    def __init__(self, *args, **kwargs):
        super(NoCommentsInlineFormset, self).__init__(*args, **kwargs)
        self.queryset = ChangeComment.objects.none()


class ChangeCommentInline(admin.StackedInline):
    model = ChangeComment
    extra = 1
    exclude = ("user", )
    formset = NoCommentsInlineFormset

    def save_model(self, request, obj, form, change):
        """auto-assign logined in user to comment"""
        if not change:
            obj.user = request.user
        obj.save()    


class EntryAdmin(admin.ModelAdmin):   
    inlines = (ChangeCommentInline, )

Can limiting the ChangeComment entries displayed in the Inline be done, or is there a better way to handle this?

Answer 1

As benjaoming mentioned in the comments, it was necessary to override the get_queryset() method in the InlineModelAdmin. It was not necessary to override and attach a new formset to the InlineModelAdmin definition as I initially thought.

Here is the resulting implementation:

class ChangeCommentInline(admin.StackedInline):
    """For allowing logged in user to add change comment"""
    model = ChangeComment
    extra = 1
    exclude = ("user", ) # auto-update user field in save_formset method of parent modeladmin.


    def get_queryset(self, request):
        """Alter the queryset to return no existing entries"""
        # get the existing query set, then empty it.
        qs = super(ChangeCommentInline, self).get_queryset(request)
        return qs.none()