#26800: Model FormSet & Prefetch ordered
-------------------------+-------------------------------------------------
Reporter: | Owner: nobody
amille44420 |
Type: | Status: new
Uncategorized |
Component: | Version: 1.9
Uncategorized | Keywords: formset preferch order_by ordered
Severity: Normal | model
Triage Stage: | Has patch: 0
Unreviewed |
Easy pickings: 0 | UI/UX: 0
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I happened to meet some unexpected behavior while mixing together the
Model FormSet with a Queryset on which I had prefetch.
My setup is the following one ;
{{{
#!python
prefetch = Prefetch('childs', Child.objects.order_by('order')),
queryset = Parent.objects.prefetch_related(prefetch)
parent = queryset.get(pk=42)
formset = ChildFormSet(queryset=parent.childs.all())
}}}
Everything works without warning or error, however the formset does not
respect the queryset I provide. I tried to understand a bit more about the
reasons behind it and I finally see the folloxing lines in
BaseModelFormSet.get_queryset() ;
{{{
"!python
# If the queryset isn't already ordered we need to add an
# artificial ordering here to make sure that all formsets
# constructed from this queryset have the same form order.
if not qs.ordered:
qs = qs.order_by(self.model._meta.pk.name)
}}}
So I went to read my queryset object and I saw that the property ordered
is to False while the results are correctly ordered (the property
_prefetch_done is True on my queryset object). So my thinking is that the
queryset resulting of parent.object.all() is my prefetch (as expected) but
not ordered as my FormSet expects. So it does order it by the primary key
for the model and breaks my prefetch.
I checked twice on the documentation and source code but I didn't see any
warning about putting together prefetch & formset, especially on ordered
queryset.
--
Ticket URL: <https://code.djangoproject.com/ticket/26800>
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